HIV and AIDS Flashcards
HIV-1 was discovered in what year?
1981
HIV-1 and HIV-2 belongs to what genus and family?
genus: Lentivirinae, family: Retroviridae
HIV-1 and HIV-2 are two diff strains (T/F)
True
HIV-1 and HIV-2 are transmitted the same way (T/F)
True
HIV-2 is easier to transmit (T/F)
False
HIV-2 progresses faster than HIV-1 (T/F)
False
HIV-2 is found in ____ ______ and rarely found anywhere else.
West Africa
Morphology of HIV-1 and HIV-2
- enveloped positive-strand RNA viruses, with diameter of about 110nm
Infective particles are called?
Virions
Virions, contain two identical copies of single-stranded RNA (T/F)
True
Mother to child transmission in HIV-2 is low (T/F)
True
• Two groups, __ and __ have been found in
HIV-1. Group M is further divided into 10
subtypes _ - _.
Two groups, M and O have been found in
HIV-1. Group M is further divided into 10
subtypes A - J
The strains of HIV-1 can be classified into four groups.
Of these, M is the ‘major’ group and is responsible for the majority of the global HIV epidemic.
The other three groups - N, O and P - are quite uncommon.
Group O represents up to 5% of infections in several west and central African countries, and Group N and P have been rarely identified in Cameroon. All groups can be detected by HIV-1 antibody tests.
How many sub-types are in HIV-2?
5 subtypes, A - E
Hemagglutinins - define
glycoproteins which cause red blood cells (RBCs) to agglutinate or clump together
HIV-2 strains can’t be found with HIV-1 test (T/F)
True
Subtypes A, C, and D
being the most prevalent in ?
Sub saharan Africa
Subtypes A, C, and D being the most prevalent in ?
Sub saharan Africa
Which subtypes are recombinant with subtype A in HIV-1?
all available sequences of subtype E & G are recombinant with subtype A
New HIV infections have been reduced by ___ since the peak in ____
New HIV infections have been reduced by 40% since the peak in 1998
AIDS-related deaths have been reduced by ___ since
the peak in ____.
AIDS-related deaths have been reduced by 60% since
the peak in 2004.
Women who experienced physical / sexual partner violence are 1.5 times more likely to acquire HIV than women who have not experienced such violence (T/F)
True
Virally suppressed - define
When antiretroviral therapy (ART) reduces a person’s viral load (HIV RNA) to an undetectable level.
Does viral suppression indicate that a person is cured?
No
Every week, around ___ young _____ aged __ to __ years become infected with HIV.
Every week, around 5500 young women aged 15–24 years become infected with HIV.
In sub-Saharan Africa, five in six new infections among
adolescents aged 15–19 years are among girls. (T/F)
True
Young men aged 15–24 years are twice as likely to be living with HIV than women. (T/F)
False; Young women aged 15–24 years are twice as likely to be living with HIV than men.
Risk factors in acquiring HIV
Gay men
Drug users
Sex workers
Transgenders
Leading cause of death among persons with HIV
Tuberculosis
What kind of therapy is recommended to persons living with HIV who experience no TB symptoms? And what would this therapy do?
People living with HIV with no TB symptoms need TB
preventative therapy
- The therapy lessens risk of developing TB and reduces TB/HIV death rates by around 40%.
At the end of ____, US$ ___ billion was available for the AIDS response in _____________income countries, almost US$ ___ billion less than in 2017.
At the end of 2019, US$ 18.6 billion was available for the AIDS response in lowand middle-income countries, almost US$ 1.3 billion less than in 2017.
When was the 1st case of AIDS diagnosed in TnT?
1983
Seroprevalence - define
level of a pathogen in a population, as measured in blood serum.
Study of 100 Homosexual/Bisexual men at the main STD Clinic in TnT showed what results? And was conducted in what year?
HIV Seroprevalence : 40%
Risk Factor for HIV : Sexual contact with a North American
Male.
1983/1984
When was the test for antibodies made available in TnT?
1984/1985
When were the 1st AIDS cases diagnosed in women and children in tnt?
1985
Since 1985: There has been a rapid transition to a
predominantly heterosexual HIV/AIDS epidemic. (T/F)
True
Why are viruses so difficult to treat with antibiotics?
- Because you’d have to destroy the host cell since viruses replicate inside host cells
- Antibiotics interfere with specific mechanisms of a cell such as protein synthesis or respiration or cell wall pores, the viruses don’t have the same membrane bound organelles or chemical reactions as bacteria to antibiotics.
So the mechanisms needed for antibiotics to act would not be present in viruses.
HIV consists of what structures?
Core, capsid, envelope, protein attachments
The core consists of?
RNA, reverse transcriptase
Envelope consists of?
Lipid membrane from host cell - extra outer layer
Protein attachments
On exterior of envelope
Enables virus to attach to T helper cell
CD4 is expressed on which cells?
T cells, dendritic cells, and macrophages
How does HIV bind to cells?
Via CD4 which is expressed on T cells, dendritic cells and macrophages – HIV binds and enters cells
If approximately 10^10 HIV particles are produced daily and about 10^9 CD4 cells are destroyed every day. What will happen overtime to the CD4 cell count?
It will decrease overtime
Main genes that are found in the envelope of HIV
Gp160, Gp120, Gp41
Gp160 is encoded by?
ENV (envelope) gene
How is Gp120 and Gp41 formed?
Gp160 is cleaved after translation by host enzymes in the Golgi Body to form Gp120 (SU/surface) and Gp41 (TM/transmembrane)
SU
surface
TM
transmembrane
Gp41 vs GP120
Gp 41 is embedded in the membrane; – fusion protein
Gp120 is not but is held to Gp41 by non-covalent
interactions. – main receptor of HIV that binds to CD4 molecules on host cell
Coreceptor define
A co-receptor is a cell surface receptor that binds a signalling molecule in addition to a primary receptor in order to facilitate ligand recognition and initiate biological processes, such as entry of a pathogen into a host cell.
Gp120/41 functions as the viral antireceptor or attachment protein to CD4 binding on which coreceptors?
CCXR4 & CCR5
Gp120 is easily shed from the virus particle (T/F)
True
What aspect of Gp120 poses an issue for vaccines?
Large num of sugar chains on Gp120
Fusogen - define
glycoproteins that facilitate the fusion of cell to cell membrane
Internal structures - are encoded by which gene?
These are all encoded by the gag (group-specific antigen) gene
How is the gag gene made?
- it is made as a polyprotein
- it is cleaved after budding of the virus by a virally encoded protease (protein synthesis) encoded by the pol gene.
GAG polyprotein is cleaved to three proteins that are found
in the mature virus’?
MA (matrix, p17),
CA (capsid,p24),
NC(nucleocapsid,p6,9).
POL polyprotein is cleaved to:
PR(protease),
RT (reverse transcriptase),
IN (integrase)
GAG polyprotein is cleaved to three proteins that are found in the mature virus, which are?
MA (matrix, p17),
CA (capsid,p24),
NC(nucleocapsid,p6,9).
POL polyprotein is cleaved to:
PR(protease),
RT (reverse transcriptase),
IN (integrase)
–> The cleaving activates the enzymes
ENV encodes for?
Envelope polyproteins - gp120, gp41
Gp160
The polyproteins will be joined to form envelope glycoproteins Gp120 and Gp41 (T/F)
False; the polyproteins are cleaved by proteases to form glycoproteins Gp120 and Gp41
Gp160 is cleaved to form Gp120 and Gp41 (T/F)
True
What structure does Gp120 form on envelope?
Gp120 forms knobs protruding from outer envelope
What is the fate of Gp41 in envelope?
Gp41 is a transmembrane glycoprotein antigen on the inner + outer membrane & attaches to Gp120
Which structures are involved in fusion and attachment of HIV to CD4 antigen on host cells?
Gp120 and Gp41
Matrix (P17) lines the inner surface of viral membrane to which it is attached by covalently bound myristic acid (T/F)
True
In addition to the three protein derived
from GAG, POL and ENV, there are six
other proteins made by HIV, which are?
Internal Structure Proteins:
–incorporated into the virus
(Vif, Vpr and Nef)
–others (Tat, Rev and Vpu) are not found in the mature virus.
Functions of Tat, Rev and Vpu
Tat and Rev are regulatory proteins and
Vpu indirectly assists in assembly
Match protein produced to gene encoding it Protein Gene Vif NEF Vpr TAT Nef REV Tat VPR Rev VPU Vpu VIF
Protein Gene Vif VIF Vpr VPR Nef NEF Tat TAT Rev REV Vpu VPU
TAT and REV stands for?
TAT: Trans-Activator of Transcription
REV: Regulator of Virion protein expression
NEF and VIF stands for?
NEF: Negative Regulatory Factor;
VIF: Virion Infectivity Factor
VPU and VPR stands for?
VPU: Viral Protein U;
VPR: Viral Protein R
One of three possible ways of reading a nucleotide
Reading frame
Find the possible reading frames of
acttacccgggacta
We can start from the 1st, 2nd or 3rd letter
1st: act tac ccg gga cta
2nd: ctt acc cgg gac
3rd: tta ccc ggg
Why is it okay for internal structure genes to overlap with ENV genes?
They are in different reading frames
TAT and REV genes were established to be important for virus production, what evidence is there?
Mutants present in TAT and REV
RNA polymerase II - define
RNA polymerase II is a multiprotein complex that transcribes DNA into precursors of messenger RNA (mRNA)
TAT gene product binds to a sequence in all of the genes of HIV and positively stimulates transcription by stimulating elongation by RNA Pol II . What process does it regulate?
TAT gene is a positive regulator of protein synthesis, including its own synthesis
REV binds to an element only in the mRNA for structural
proteins (GAG/POL/ENV), how does the binding affect the structural proteins and non-structural proteins?
Regulates the ratio of GAG/POL/ENV to non-structural, controlling protein (TAT/REV) synthesis.
How does REV regulation work?
When REV levels are high, structural
protein synthesis rises and controlling protein synthesis
falls. Thus, REV inhibits its own production and that of TAT.
Result of cleavage of proteins is?
Cleavage of a single specific peptide bond transforms the protein from a catalytically inactive form into one that is fully active.
Provirus - define
Form of a virus that is integrated into the genetic material of a host cell and by replicating with it can be transmitted from one cell generation to the next without causing lysis
What is homeostasis in relation to HIV immune response?
Homeostasis of T cells - Maintaining and restoring T cell numbers via T cell depletion/expansion
(Governed by extrinsic signals mostly cytokines)
Homeostasis leads to problems for the parasitic provirus, how?
- Super-infection by other HIV particles which bind to
surface CD4 antigen of the infected cell may kill the cell. - Probably more importantly, virus bound via CD4 or free Gp120 bound to CD4 = cell having an immune attack and potential destruction
Th1, Th2, Th17 (target specific classes of pathogens) and regulatory T cells to maintain self-tolerance and follicular helper T cells (TFH) that provide help to B cells for antibody - these subsets are for what type of T cell?
Tc1, Tc2, Tc9, Tc17, Tc22 (most release cytokines) - what type of T cell?
CD4+ subsets
CD8 subsets
How does T cell homeostasis affect CD4+ T cells?
Homeostasis of T cells can be defined as the ability of the immune system to maintain normal T-cell counts
T-cell homeostasis is independent of CD4+ and CD8+ subsets
Because the actions of the subsets are not reliant on T cell homeostasis
–> then the failure of homeostasis won’t be accounted for
–>and CD4+ T cells will continue to decrease. as HIV infects those cells and they become destroyed
(as mentioned 2 slides above)
there is no regeneration.
What is a domain?
- Functional and/or structural units in a protein.
- Responsible for a particular function or interaction, contributing to the overall role of a protein.
What is one of Fas cell signalling pathway roles?
Fas cell signaling pathway has a central role in the physiological regulation of programmed cell death (also called apoptosis)
What is Bcl-2?
Bcl-2 is found in BH3 domain
- it is a substrate of Casp8 in Fas apoptotic signalling pathway
When a cell is already infected and becomes infected by other HIV particles, how do the virus proteins respond and what is the outcome?
Env binds to CD4 and CXCR4 or CCR5 induces Caspase 3 activity
Tat upregulates Fas pathway, increasing Caspase 8 activity
Tat decreases Bcl-2 (substrate of Casp8) expression - regulation.
Vpr and Vif causes apoptosis
HIV protease cleaves Bcl-2
Outcome by host: Cytotoxic T Lymphocyte (CTL) killing of infected cell
Downregulation - define
An decrease in the number of receptors on the surface of target cells, making the cells less sensitive to a hormone or another agent.
Functions of NEF
- Downregulation of CD4 antigen
- Reduces surface expression of MHC I = altered Ag presentation by infected cell = infected cell protected from cytotoxic T cell attack
- NEF (derived from negative factor) -Virus produced in the presence of NEF is a little more infectious than virus produced in its absence
- Important role in HIV replication
MIP-1α and MIP-1β function
These are two chemokines that bind to the co-receptors
for HIV infection of macrophages but here these
chemokines have another function.
Function of MIP-1α and MIP-1β in HIV
How are these chemokines secreted by Nef aiding in HIV replication?
•HIV-infected macrophages secrete MIP-1α and MIP-1β.
(These chemokines have a diff f’n in HIV)
•– They cause resting CD4+ T cells to migrate (undergo
chemotaxis) towards the infected macrophages.
Thus Nef has a positive effect on viral infection and replication by promoting the survival of infected cells.
*** HIV does not have a very long half-life in the circulation before becoming non-infectious. – So this function is important
Molecules other than CD4 antigen that have an important role in binding
Chemokine receptors (a family of proteins on the surface of immune cells CCR5) are the partner with CD4 in allowing entry into macrophages.
The chemokine receptor is the primary receptor for HIV (T/F)
True
Role of CD4 is to?
concentrate virus at the cell surface and
facilitate interaction with the chemokine
receptor
CXCR4 / fusin is also a ______ for HIV in otherwise noninfectable ___ cells
is also a coreceptor for HIV in otherwise noninfectable CD4+ cells.
CXCR4 is a G protein-coupled ________ whose ligand is a _ cell _________ factor
Why is it called fusin?
CXCR4 is a G protein-coupled receptor
whose ligand is a B cell stimulatory factor-
- because it promotes the infection/fusion of CD4+ cells.
The amount of fusin on the cell surface may explain differences in tropism and fusin seems to be more active in T cells than in macrophages. (T/F)
True
Fusin uses two chemokine receptor molecules as coreceptors for the two types of cells that are preferentially infected
- CCR5 on macrophages and dendritic cells and
* CXCR4 on lymphocytes
In the absence of these co-receptors, HIV is unable to successfully enter the cells (T/F)
True
A small percentage of individuals of Caucasian descent express CCR5 and are protected from infection by HIV (T/F)
A small percentage of individuals of Caucasian descent fail to express CCR5 and are protected from infection by HIV
CCR5+ dendritic cells - define
- protein on the surface of WBCs ; acts as a receptor for chemokines.
Infection of CD4+ CCR5+ dendritic cells appears to be the primary route of initial infections (T/F)
True
Infection of CD4+ CXCR4+ T cells occurs earlier in the disease process (T/F)
False; Infection of CD4+ CXCR4+ T cells occurs later in the disease process
Cis vs Trans infection
Cis - Direct virus-cell - Fusion, replication. budding Trans - Transport of virus - Via endo and exosomes - DC SIGN
Intraepithelial dendritic cells - define
The gut epithelium is populated by intraepithelial lymphocytes (IELs), T cell population with cytotoxic and regulatory properties
Role of DC in HIV
DC can transport HIV to permissive cells in lymph node - Trans inf
HIV entry into lymph node CD4 T cells
- Intraepithelial cells bind HIV using DC SIGN
- HIV internalized into early endosomes
- Dendritic cells that have migrated to lymph nodes transfers HIV to CD4 T cells
T cell activation occurs via what cells and where?
T cells can receive signals during both short-lived and long-lived interactions with antigen-bearing DCs in lymph node
Viral integration into host nucleus process
- Virus particle binds to CD4 receptor and coreceptor on T cell
- Viral envelope fuses with cell membrane allowing entry of viral RNA
- Reverse transcriptase copies viral RNA -> ds cDNA
- Viral cDNA enters nucleus and incorporated into host DNA
Production of proteins following viral integration - process
- T cell activation (via DC SIGN) induces low level transcription of provirus
- RNA transcripts multiply spliced - allowing translation of early genes - Tat and Rev
- Tat amplifies transcription of viral RNA – Rev >’s transport of singly spliced / unspliced viral RNA to cytoplasm
- Translation of late proteins (Gag, Pol, Env) which assemble into virus particles which bud from cell
Gag - group specific antigen - gene function
Encodes capsid structural proteins/core protein + matrix proteins
Pol - polymerase - gene function
Encodes
- Reverse transcriptase, Integrase, Protease
Env - envelope - gene function
Encodes
- Envelope glycoproteins – Gp120 and Gp41
Gp 120 - binds CD4 and CCR5
Gp41 - virus fusion and internalization
Tat - transactivator - gene function
Pivotal role in HIV-1 replication since it stimulates transcription from the viral long terminal repeat (LTR) promoter
Rev - regulator of viral expression - gene function
Allows export of unspliced and partly spliced transcripts from nucleus -
– nuclear localization signal encoded in rev; allows Rev to be localized to the nucleus, where it is involved in the export of unspliced and incompletely spliced mRNAs.
Vif - gene function
Affects particle infectivity
- disrupt the antiviral activity of the human enzyme APOBEC; targets it for cellular degradation.
Vpr - gene function
Transport DNA to nucleus
-transport the preintegration complex into the nucleus where the process of viral integration into the host genome is completed
Vpu - gene function
- degradation of the CD4 molecule in endoplasmic reticulum and enhancement of virion release from cells.
Nef - gene function
Augments viral replication in vivo and in vitro
Downregulation of CD4 antigen
Reduces surface expression of MHC I and II
How does HIV affect CD4 count?
• The body produces new CD4 cells
• HIV viruses use CD4 cells to replicate more
viruses
• Slowly, over time, CD4 cells are killed by the virus
Normal range for CD4 count is ?
600-– 1500 cells/mm^3
CTL - function in HIV
Cytotoxic T lymphocytes (CTLs) have been suggested to play an important role in controlling human immunodeficiency virus (HIV-1 or simply HIV) infection. HIV, due to its high mutation rate, can evade recognition of T cell responses by generating escape variants that cannot be recognized by HIV-specific CTLs
p24 test
An antigen test checks your blood for an HIV antigen, called p24.
When you’re first infected with HIV, and before your body has a chance to make antibodies to the virus, your blood has a high level of p24.
The p24 antigen test is accurate 11 days to 1 month after getting infected.
4 weeks to 2 years - antibodies against HIV Env trend
Antibodies against HIV Env – rises abruptly then plateaus
4 weeks to 2 years - HIV specific CTL
HIV specific CTL – Rise then fall a little then plateau
4 weeks to 2 years - Antibodies against HIV p24
Antibodies against HIV p24 – slight elevation, plateau
4 weeks to 2 years - Infectious virus in plasma
Infectious virus in plasma – Huge increase, huge decrease, constant fluctuations
All factors decrease at 0-1 years except ‘infectious virus in plasma’
Normal range for CD4 cells
•Normal range : 500 – 1400 cells/mm3
Lowest and peak values - times - CD4 count
Diurnal changes with lowest levels at 12.30pm and
peak values at 8.30pm.
When are there small decreases in CD4 counts?
Acute infections and major surgery
When are there large decreases in CD4 counts?
Acute corticosteroid administration
When are there deceptively high CD4 counts?
- patients with HTLV-1(cousin of HIV)/HIV co-infection
- those with a splenectomy
Goals of HIV therapy
- Maximal and durable suppression of viral load
- Restoration and/or preservation of immunologic function
- Improvement of quality of life
- Reduction of HIV-related morbidity and mortality
- Maximize adherence
- Rational sequencing of therapy
- Preservation of future treatment options
- Use of resistance testing in selected clinical settings
ARVs - define
The drugs used to treat HIV are called antiretroviral drugs (ARVs).
HIV treatment is made up of three or more antiretroviral drugs normally combined into one pill.
Impact of ARVs
Fewer deaths due to HIV but infections affecting patients continue to rise
Transmission of HIV depends on?
- closeness of contact with
- frequency of exposure to the source of infection
Modes of transmission of HIV
- unprotected heterosexual intercourse
- unprotected sex between sex workers and clients
- perinatally from mother to child or breast milk and parenteral inoculation
Risk factors of HIV
- Multiple sexual partners
- Those receiving blood or blood products e.g. haemophiliacs, organ transplants
- Unborn child of HIV positive mother
- Medical professionals, needle stick injuries
- Intravenous drug users, drug addicts
Criteria of diagnosis of AIDS
(a) a CD4+ T cell count less than 200 cells/mm^3
(b) the presence of at least one of the 26 different
opportunistic infections, such as
(i) Pneumocystis carinii pneumonia,
(ii) Candida esophagitis
(iii) Toxoplasmosis
(iv) Cryptococcal meningitis
(v) Tuberculosis caused by M. tuberculosis
HIV disease progression
- Viral transmission
- Primary HIV infection (Acute Retroviral Syndrome)
- Seroconversion ( period during which the body starts producing detectable levels of HIV antibodies; fever + body aches)
- Asymptomatic chronic infection
- Symptomatic HIV infection (Rash, chills, night sweats, swollen lymph nodes, mouth ulcers)
- AIDS (Rapid weight loss, Recurring fever or profuse night sweats, Extreme and unexplained tiredness, Pneumonia)
- Advanced HIV infection/AIDS (CD4 < 50/mm3)
Overview of HIV replication
- Virion adsorption to a receptor (HIV attaches itself to recepts on surface of CD4 cell)
- HIV envelope and CD4 membrane fuse together allowing entry of HIV into cell
- Penetration and uncoating in the cytoplasm
- Reverse transcription in the cytoplasm (Conversion of HIV RNA –> HIV DNA)
- Integration of provirus into the nucleus and full transcription (conversion allows HIV to enter CD4 cell nucleus,
integrase secreted by HIV allows insertion of HIV DNA into CD4 cell DNA;
HIV proteins made using CD4 cell machinery) - Translation in the cytoplasm and capsid assembly (new HIV proteins and HIV RNA move to cell surface and assemble into immature HIV)
- Budding out of the cell and maturation in circulation (protease secreted which breaks down long HIV protein chains making virus mature)
Clonal deletion - define
- Removal through apoptosis of B cells and T cells that have expressed receptors for self before developing into fully immunocompetent lymphocytes.
- prevents recognition and destruction of self host cells,
During HIV infection, there is a large loss in immune response to HIV since CD4+ cells are infected, what happens to immature T cells?
Thus, there is clonal deletion leading to tolerance.
The cells that proliferate to respond to the virus are infected and killed by it
- Immature T cells expressing receptors for self would be left and those would be killed by clonal deletion
Antigenic determinant - define
Part of an antigen recognized by the immune system, specifically by antibodies, B cells, or T cells
Epitope variation -
Different antibodies can be made that recognize different epitopes on the same molecule.
An antigen is an antigen when there is at least 1 epitope, but there is not a specific number of epitopes on one antigen.
The number of epitopes depends for example on the size of the antigen
Epitope variation in hiv - effect
Epitope variation can lead to escape of HIV from the immune response
Effect of immune response loss = destruction of CD4+, describe
Activated T cells are susceptible to apoptosis. Spontaneous apoptosis of uninfected CD4+ and CD8+ T cells occurs in HIV-infected patients.
What causes diminished capacity to stimulate CD4+ cells?
The number of follicular dendritic cells falls over time, resulting in diminished capacity to stimulate CD4+
cells
The relentless decline of CD4+ cells occurs from the beginning of infection and is permanent (T/F)
True
There is no decline of CD8+ cells in AIDS (T/F)
False; Near the end stage of AIDS, CD8+ cells also decline
Most CD4+ cells are never actually infected by the virus but die from some other means (T/F)
True
Immune abnormalities in HIV infection - list
(a) Altered cytokine expression
(b) Decreased CTL and NK cell function
(c) Decreased humoral and proliferative response to
antigens and mitogens
(d) Decreased MHC-II expression
(e) Decreased monocyte chemotaxis
(f) Depletion of CD4+ cells
(g) Impaired delayed type hypersensitivity (DTH) reactions
(h) Lymphopenia
(i) Polyclonal B-cell activation
Loss of function of CD4 cells
CD4+ T cells which bound to gp120 may not be available to interact with class II major histocompatibilty complex (Class II MHC) molecules on antigen presenting cells (APCs), thus T cell responses to antigens would be inhibited. Alternatively, gp120 binding to CD4+ may deliver signals that downregulate helper T cell function.
Loss of function of CD4 cells
HIV-infected T cells are unable to form tight synapses with APCs, therefore interferes with T cell activation. Failure of the activation process will lead to incapability of the T cells particularly CD4+ T cells to interact with other immune cells and subsequently lead to failure of elimination of the virus
Cytokines play an important role in controlling the homeostasis of the immune system (T/F)
Cytokines play an important role in controlling the homeostasis of the immune system.
Altered cytokine expression
Cytokine production can increase viral replication due to its activation role in HIV infected cells [16]. Such cytokines include IL-2, IL-4 and interferon type II (IFN-γ) which primarily are required for expansion aid of antiviral T cells and antibody responses
Decreased humoral and proliferative response to
antigens and mitogens
T-helper 2 (Th2) cytokines required for extracellular infection such as IL-4, IL-10, proinflammatory cytokines (IL-1, IL-6, IL-8) and tumour necrosis factor (TNF)-alpha, is increased
Th2 cytokines also may inhibit macrophage-mediated killing of microbes and consequently lead to failure of macrophage activation in the killing process of the virus.
HIV effect on brain
gp120 can kill off brain cells by disrupting their internal chemistry.
gp120 also slows production of new brain cells in the
hippocampus, a brain region central to learning
and memory.
HIV effect on heart
Secondary infections that affect the heart muscle and pericardial sac have a greater chance of occurring in people with compromised immune systems.
Some medications used to treat HIV patients have heart-related side effects, what does this mean?
As drug therapy improves and prolongs the lives of HIV
and AIDS patients, the number of HIV-positive cardiac
cases will rise.
What is a method HIV uses to shield itself from effects of ARVs?
HIV can shield itself from the effects of antiretroviral
drugs by hiding in the outer lining of the gut.
The virus continues to copy itself in the gut mucosa,
suppressing immune function in patients treated with
anti retrovirals, even when the treatment is working
elsewhere in the body
HIV disease can result in kidney failure due to HIV
infection of kidney cells (T/F)
True
AIDS is end stage and the two clinical stages before are?
Before this end stage, there are initially two clinical stages, the primary HIV infection and the latent or post seroconversion (asymptomatic stage)
In acute infection, HIV is ___ limiting in some patients
Self limiting (any disease whose natural history is to resolve without treatment )
Acute retroviral syndrome (ARS) - define
First stage of infection with the human immunodeficiency virus (HIV).
Immune response in ARS
There is an initial fall in CD4+ cells and a rise in CD8+
cells but the numbers quickly return to near normal.
Cytotoxic B and T lymphocytes mount a strong defense
and virus largely disappears from the circulation.
CD4 cell numbers aren’t greatly affected since their production numbers are greater than their destruction
When does seroconversion occur?
Seroconversion occurs between 1- 4 weeks after
infection.
Clinical latency - HIV
Because of the strong immune defense, the number of
viral particles in the blood stream declines and the
patient enters clinical latency.
Little virus can now be found in the bloodstream or in peripheral blood lymphocytes.
At clinical latency, even though the viral particles are low in the blood, where else can the virus be found?
Follicular dendritic cells in lymph nodes - here viral replication continues.
What happens to HIV in lymph nodes and how do CD4+ cells counteract?
- The virus is also replicated by macrophages.
- A small fraction of the productively infected CD4+ cells may survive long enough to revert to the resting memory state (as do uninfected CD4+ memory cells).
AIDS stage affects only certain body systems (T/F)
False
AIDS is not the only oncogenic result of HIV
pathogenesis , what else has it caused?
it has also caused a variety of haematopoetic and neurological conditions, including: Paralysis, Wasting, Ataxia, Arthritis, Dementia, Depression, Neuropathy
HIV body samples
blood, CSF, pleural fluid, saliva, urine
HIV test types
(a) immunological: testing for HIV-specific antibodies;
(b) functional: detecting enzymatic activity and
(c) molecular: detecting viral DNA materials
The time to positivity in antibody tests (i.e. to sero
conversion) depends on
The infectious dose,
The transmission mode and
The sensitivity of the antibody assay
HIV Tests
(a) Rapid tests (OraQuick, Reveal G3, Uni-Gold Recombigen, Multispot)
(b) ELISA/EIA tests, Western blots
(c) Molecular testing – detection of HIV DNA:
(i) PCR
(ii) NASBA (nucleic acid sequence-based amplification)
(iii) DNA probes, a signal-amplification
procedure involving branched DNA probes
(bDNA)
(d) Viral isolation – this is too inefficient, time
consuming and costly for use as a routine
diagnostic tool for HIV infection.
(e) Treatment monitoring - CD4+ count, viral
load determination
HIV prevention
(a) Make voluntary HIV testing a routine
part of medical care
(b) Implement new models for diagnosing HIV infections
outside medical settings
(c) Prevent new infections by working with persons
diagnosed with HIV and their partners
(d) Further decrease perinatal HIV transmission
Name 4 FDA approved rapid HIV tests
OraQuick Advance
Uni-Gold Recombigen
Reveal G2
Multispot (testing HIV-2 also)
Sensitivity and specificity range between 98.6-100
Sensitivity vs specificity of a test
Sensitivity: the ability of a test to correctly identify patients with a disease.
Specificity: the ability of a test to correctly identify people without the disease.
OraQuick Advance HIV-1 and 2 - features
- CLIA-waived for finger stick, whole blood, oral fluid; moderate complexity with plasma
- Store at room temperature
- Screens for HIV-1 and 2
- Results in 20 minutes
“CLIA” is the acronym for the Clinical Laboratory Improvement Amendments of 1988. This law requires any facility performing examinations of human specimens (e.g., tissue, blood, urine, etc.) for diagnosis, prevention, or treatment purposes to be certified by the Secretary of the Department of Health and Human Services.
OraQuick Advance - method
Obtain finger stick specimen
Insert loop into vial and stir
Insert device into buffer
Collect oral fluid specimens by swabbing gums with test device.
Insert device; test develops in 20 minutes
Uni-Gold Recombigen - Features
CLIA-waived for finger stick, whole blood;
moderate complexity with serum, plasma.
Store at room temp. Screens for HIV-1.
Results in 10 - 12 minutes
Uni-Gold Recombigen method
Add 1 drop specimen to well
Add 4 drops of wash solution
Wait for results
Reveal G2 - features
CLIA moderate complexity with serum, plasma. Reconstitute and refrigerate reagents.
Screens for HIV-1.
Perform test in 5 minutes
Reveal G2 - method
Centrifuge to obtain serum or plasma
Add buffer to reconstitute conjugate. (Sufficient for 15
tests; Refrigerate to store)
Add 3 drops buffer to moisten membrane
Add one drop of serum or plasma, followed by 3 drops of buffer.
Add 4 drops of Colorimetric
Detection Agent Add 3 drops of buffer to wash
Multispot HIV-1/HIV-2 - features
CLIA moderate complexity with serum, plasma. Refrigerate reagents.
Distinguishes HIV-1 from HIV-2.
Perform test in 15 mins
Multispot - method
Dilution of plasma or serum
Remove and discard pre-filter
Several timed reagent & wash steps
In which situation is rapid test appropriate to use ?
Rapid HIV testing may also be useful to quickly confirm the diagnosis of HIV infection in patients who present with an AIDS-defining illness but have unknown HIV status
HIV flowchart - slide 55
WHO Strategies of testing
All samples tested with one ELISA/Rapid
(reactive test is considered positive -)
–Signs/symptoms >30% showing
All samples tested with one ELISA/Rapid
Reactive samples tested again on diff system
(considered positive only when both assays are reactive)
–Symptomatic prevalence <30%, asymptomatic >10%
All samples tested with one ELISA/Rapid
Reactive samples from first test tested with diff antigen/prep
Reactive samples from second test tested with diff antigen/principle
(considered positive only when all three assays are reactive)
–Asymptomatic <10%
Reasons for lab tests
• A laboratory diagnosis is the only objective evidence
of HIV infection
• CD4 count is the most reliable and relevant
measure of immune status related to HIV
• Anti-retroviral drugs affect us in varied ways that
must be monitored
• We need to know if and when the virus has become
resistant to therapeutic drugs
Antibody testing is usually done on a blood sample, often using an enzyme-linked assay called an ELISA or EIA. What occurs here?
In this test, a person’s serum is allowed to react with virus proteins that have been produced in the laboratory.
What are conjugates in ELISA/EIA?
Addition of a substrate to enzyme conjugates initiates chemical rxns that subsequently will result in a product. ELISA substrates generate soluble products
Describe the 4 generations of HIV serological tests
1st Generation
Antigen consisting of viral lysases to detect IgG antibodies
2nd
Recombinant HIV proteins/antigens to detect HIV - 1/2 IgG antibodies
3rd
Sandwich EIAs; uses labelled antigen as
conjugate, Detects HIV-1, HIV-2, IgG and IgM antibodies.
4th generation
Detects both HIV antibody (IgG and IgM) and p24 antigen.
What do we refer to each generation test as?
The first- and second-generation antibody assays are now referred to as IgG-sensitive tests, third-generation assays as IgM/IgG-sensitive tests, and fourth-generation as antigen-antibody immunoassays
UniGold Recombinant HIV1/2 (Trinity biotech) is used in tnt, how long does it take for results to show?
15 mins
Tests to perform
- HIV status:
* Diagnostic screen and confirmation - Immune status:
* CD4 count - Risk of progression:
* Viral Load - Drug resistance:
* Viral genotyping/phenotyping
Primer - define
A primer is a short, single-stranded DNA sequence used in the polymerase chain reaction (PCR) technique. In the PCR method, a pair of primers is used to hybridize with the sample DNA and define the region of the DNA that will be amplified.
PCR steps
(1) denaturation, in which double-stranded DNA templates are heated to separate the strands;
(2) annealing, in which short DNA molecules called primers bind to flanking regions of the target DNA; and
(3) extension, in which DNA polymerase extends the 3′ end of each primer along the template strands. These steps are repeated (“cycled”) 25–35 times to exponentially produce exact copies of the target DNA
What happens in pcr when RNA is used as the target?
When RNA is used as the target, an initial step is employed in which the RNA is first converted to DNA using the enzyme reverse transcriptase.
Purpose of PCR for HIV
- To detect, the provirus or the viral RNA genome respectively, in plasma
PCR - what is the result of going through PCR cycles?
After one cycle, therefore, 2 daughter DNA molecules are
formed from the initial parent molecule.
By repeating this cycle 30– 40 times, an exponential growth of DNA copies is obtained to yield levels that can then be visualised.
Ways in which an infant can acquire HIV
- during pregnancy, labour or breastfeeding.
When should you test for HIV if suspected case in pregnancy?
Virological testing within the first 48 hours of life of an
HIV-exposed infant can identify infants infected in utero.
Intrapartum - define
period of care received during labor and delivery or childbirth
When to test for suspected HIV cases during late pregnancy and intrapartum?
First 48 hrs is too early to detect in 70% of cases
By age 4 weeks, virological testing approaches 98%
sensitivity.
A repeat test on a separate specimen is not necessary to
confirm an initial positive test (T/F)
False; A repeat test on a separate specimen should be done to confirm an initial positive test.
If an infant is breastfed, HIV infection cannot be
definitively excluded until the infant has a _________
diagnostic test __ months after breastfeeding has ceased completely
If an infant is breastfed, HIV infection cannot be
definitively excluded until the infant has a negative
diagnostic test six months after breastfeeding has ceased completely
How often are CD4 counts checked?
Every 6 months
What is WHO staging
The use of clinical parameters to guide clinical decision-making for the management of HIV/AIDS patients.
It was designed for use in resource limited settings where there was limited access to laboratory services
E.g.
Primary HIV infection
Asymptomatic
Acute retroviral syndrome
Clinical stage 1
Asymptomatic
Persistent generalized lymphadenopathy (PGL)
Clinical stage 2
Moderate unexplained weight loss (<10% of presumed or measured body weight)
Recurrent respiratory tract infections (RTIs, sinusitis, bronchitis, otitis media, pharyngitis)
Herpes zoster
Angular cheilitis
Recurrent oral ulceratio
Early HIV is categorized by what WHO stage and CD4 count?
-WHO stage 1 – 3 and CD4 count>500
Intermediate disease is categorized by what WHO stage and CD4 count?
- WHO stage 1 or 2 and CD4 201-500
- WHO stage 3 and CD4 351-500
Advanced HIV is categorized by what WHO stage and CD4 count?
- All patients with CD4 = 200
- WHO stage 3 and CD4 = 350
- All patients with WHO stage 4
Eligible for ART treatment
Absolute CD4 count - describe
Measurement of how many functional CD4 T-cells are circulating in your blood.
The lower the absolute CD4 count, the weaker the immune response.
Measured by a simple blood test, the results of which are reported as the number of CD4 cells per cubic millimeter of blood.
Range of absolute CD4 counts
Normal: 600 to 1200 cells per cubic millimeter
Immune suppressed: Less than 500 cells per cubic millimeter
Advanced HIV infection: Less than 200 cells per cubic millimeter
CD4 percentage - describe
CD4 percentage represents the percentage of total lymphocytes that are CD4 cells and is measured using the same blood test as that for the absolute CD4 count.
Range of CD4 percentage counts
HIV-negative people will have a CD4 percentage of about 40 percent, while HIV-infected people’s CD4 percentage can be as low as 25 percent or less.
Absolute CD4 count tends to vary within an individual child more than % CD4+ (T/F)
True
%CD4+ values vary more with age
False; %CD4+ values vary less with age
ART - what does it involve
ART involves taking a combination of HIV medicines (called an HIV treatment regimen) every day.
Goal of ART
- To reduce the plasma HIV RNA levels to an undetectable level.
Ideally, the HIV RNA level should decline rapidly after initiation of ART.
Typical range goal for reduction of plasma RNA levels
typical goal is a 1 to 2 –log reduction within 4 to 8 weeks (e.g., from 50,000 copies per ml to 500 copies per ml).
If failure to achieve the target level of less than 50 copies per ml after 16 to 24 weeks of treatment should consider what possibilities?
Drug resistance, inadequate drug absorption or poor compliance.
Viral load - define
HIV-1 viral load refers to the number of viral particles found in each millilitre. (use of PCR)
The more HIV-1 viral particles in the blood, the faster the CD4+ T-cells are likely destroyed and the faster the progress toward AIDS.
HAART stands for
Highly Active Antiretroviral Therapy
Diff classes of HAART
- Nucleoside Reverse Transcriptase Inhibitors (NRTI)
- Nucleotide Reverse Transcriptase Inhibitor
- Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs)
- Protease Inhibitors
- Fusion inhibitors
- CCR-5 co-receptor antagonists
- Integrase Inhibitor
NRTI - MoA and examples
These drugs inhibit viral RNA-dependent DNA polymerase (reverse transcriptase) and are incorporated into viral DNA (they are chain terminating drugs).
• They include (a) Abacavir (b) Didanosine
(c) Emtricitabine (d) Lamivudine (e)
Stavudine and (f) Zalcitabine (g) Zidovudine
Nucleotide Reverse Transcriptase Inhibitor - MoA and examples
• Tenofovir is the only major drug in this group
inhibit reverse transcription by causing chain termination after they have been incorporated into viral DNA. For these drugs to be active they need to be phosphorylated intracellularly.
•Has headache, nausea, diarrhoea and malaise as its most common side effects
• But its most significant side effects include Black box warning (adverse effect)– severe exacerbations (worsening) of hepatitis B reported in patients who
stop taking the drug
Non-Nucleoside Reverse Transcriptase Inhibitors - MoA and examples
NNRTIs are not incorporated into viral DNA; they inhibit
HIV replication directly by binding noncompetitively to reverse transcriptase.
They include (a) Delavirdine (b) Efavirnenz and (c) Nevirapine
Protease Inhibitors
• These drugs are specific for the HIV-1 protease and competitively inhibit the enzyme, preventing the maturation of virions capable of infecting other cells
• They include (a) Atazanavir (b) Darunavir
(c) Fosamprenavir (d) Indinavir (e) Nelfinavir (f) Ritonavir (g) Saquinavir (h) Tipranavir
Fusion inhibitors - MoA and examples
- interfere with the binding and fusion between gp120 and gp41 and the CD4 molecule on the host cell
Enfuvirtide - currently available
• This has revealed some significant clinical benefit when combined with two other active drugs.
CCR-5 co-receptor antagonists - MoA and example
Maraviroc (first of a new class of drugs)
- selectively binds to the human chemokine receptor CCR5, which is present on the cell membrane. This binding prevents the interaction of HIV-1 gp 120 with CCR5-tropic HIV-1 and thereby inhibits the virus from entering the cell.
Integrase Inhibitor - MoA and example
Inhibits the activity of the integrase which impedes the insertion of HIV-1 DNA into the host cell genome. Primarily, it removes two deoxynucleotides from the 3’ end of the viral DNA.
e.g. Raltegravir
Drawbacks to HIV treatment
- expensive
- Associated with poor compliance (not regularly taking meds)
- Side effects can be very severe
- HIV resistance is common
Anti HIV chemotherapy, effective or not?
anti-HIV chemotherapy does not stop infection and
is unlikely to cure the infected host
Best outcome for HIV
Suppression of virion production making AIDS a more
tractable (easy to control) disease
Difficulty in creating vaccine for HIV
A vaccine targets a virus in a particular form. If the virus changes, the vaccine may not work on it anymore. HIV mutates quickly
