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Phase 2 - Immunology (ICS) Flashcards

1
Q

What is the purpose of the immune system

A

To distinguish between self and non-self and protect self from non-self

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2
Q

What is the immune system made up of

A

Cells and soluble factors

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3
Q

Characteristics of the innate system

A

First line of defence
Barrier to antigen
Instinctive
Present from birth
Non-specific
Slow response
No memory

Independent of lymphocytes (but does include phagocytes and monocytes/macrophages)

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4
Q

Characteristics of adaptive system

A

Specific
Aquired/learned (from initial exposure to specific non-self)
Has memory to specific antigens
Quicker response second time onwards

Dependant on lymphocytes
Antibodies

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5
Q

Which cells are involved in the innate immune system

A

Neutrophils
Eosinophils (mainly functions in parasitic reactions)
Basophils (mainly functions in allergic infections)
Monocytes (kidney shaped nucleus - only found in blood) - release cytokines and produce complement components
- become macrophages when they leave blood and enter tissues

Mast cells - involved in allergic reactions, lots of histamine involved (from blood but reside in tissue)
Dendritic cell - major antigen presenting cells (present to macrophages and t cells) - found in epithelium

(Things like skin, tears, mucocilliary escalator are all part of innate response)

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6
Q

Which cells are involved in the adaptive system

A

Lymphocytes
* T cells
- T regulatory cells
- T helper cells (CD4)
- Cytotoxic T cells (CD8)
- Cytokine production
* B cells
- Plasma cells (antibody production)

Monocytes (only found in blood) - release cytokines and produce complement components

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7
Q

Cell components of the immune system

A

Lymphocytes
- T cells
* T regulatory cells
* T helper cells (CD4)
* Cytotoxic T cells (CD8)
* Cytokine production
- B cells
* Plasma cells
** Antibody production

Phagocytes
- Mononuclear cells
* Monocytes/ Macrophages
** Cytokine production
** Complement production
- Polymorphonuclear cells
* Neutrophils
* Eosinophils
* Basophils

Other cells
- Mast cells
- Natural killer cells
- Dendritic cells

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8
Q

What do soluble factors (humoral componant) of the blood consist of

A

Complement
Antibodies (aka immunoglobulins)
Cytokines
Chemokines

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9
Q

What is complement and what does it do

A
  • 20 proteins produced by the liver
  • mostly exist in an inactive state
  • activated via cascades
  • there are 3 activation pathways
  • only activated for the immune response
  • They have 3 modes of action:
  • Direct lysis
  • Attracting leukocytes to site of infection - chemotaxis (works by releasing chemotaxes - C3a, C5a)
  • Opsonisation (coating invading organism to increase the chance of them being phagocytosed)
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10
Q

Makeup of antibodies

A

Consists of 2 heavy chains and 2 light polypeptide chains
- Has a Fc region which is the same on all antibodies
- Has a Fab region (variable region) which is specific to the target and is where the binding site is located
- Can exist as free in solution or membrane bound to B cells

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11
Q

Functions of antibodies

A
  • bind to specific antigens
  • acts as adapter to link microbe to phagocyte
  • Neutralise toxins by binding to them
  • Activate complement (classical pathway)
    • Increase opsonisation and stimulate phagocytosis
    • agglutination, precipitation
      (-> cell lysis + chemoattraction)
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12
Q

Type of antibodies in blood

A

IgG
- most abundant - 75% of antibodies found in serum (small, can get almost anywhere - can CROSS PLACENTA)
- HIGHLY SPECIFIC

IgM
- large molecule (PENTAMERIC)
- only found within blood
- HIGHEST CAPACITY to ACTIVATE COMPLEMENT
- not super specific

IgA
- two versions: normal or DIMER
- dimer is in secreted substances e.g. saliva
- MUCOSAL
- MAIN Ab in COLOSTRUM and neonate gut

IgE
- BOUND to MAST cells and BASOPHILS
- involved in ALLERGIC reaction and HELMINTH infection
- production can be driven by eosinophils
- LEAST ABUNDANT in blood

IgD

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13
Q

What are cytokines and name the four main ones

A

Proteins secreted by immune and non-immune cells

  • Interferon
  • Interleukin
  • Colony stimulating factor
  • Tumour necrosis factor
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14
Q

What are interferons, where are they released from and what do they do?

A
  • type of cytokine
  • IFN alpha and beta produced by infected cells
  • IFN gamma produced by activated T cells
  • induces antiviral resistance in uninfected cells
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15
Q

What are interleukins, where produced and function

A

type of cytokine
Product of many cells
around 35 diff types

Pro (IL1) or Anti inflammatory (IL10)
Can cause:
- Cell division
- Cell differentiation
- Cell secretions

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16
Q

What are colony stimulating factors and what do they do

A

type of cytokine
Directs division and differentiation of bone marrow stem cells
- can have specific interleukins for specific leukocytes

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17
Q

What is tumour necrosis factor, where is it released and what does it do?

A

Type of cytokine
- TNF alpha and beta

  • released by macrophages
  • proinflammatory (especially TNF alpha)
  • mediate cytotoxicity
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18
Q

What are chemokines

A

Leukocyte cheoattractants

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19
Q

What is the innate system composed of

A

Physical and chemical barriers
Phagocytic cells
Blood proteins
- Complement

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20
Q

What happens during an inflammatory response to physical trauma

A

Coagulation
Leukocyte recruitment - acute inflammation
Kill pathogens
Clear dead cell
Prolifereation of cells to repair
Remodel extracellular matrix - remove clot

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21
Q

What is inflammation, what does it result from

A
  • series of reactions that brings cells and molecules of immune system to sites of infection and damage
  • can result from tissue damage and/or infection
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22
Q

What are the 3 key processes of inflammation and subsequent hallmarks of inflammation?

A

Increased blood supply
Increased vascular permeability
Increased leukocyte transendothelial migration (Extravasation)

Hallmarks of inflammation:
- red
- swelling
- heat

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23
Q

Which cells are associated with recognising non-self?

A

In blood:
- Monocytes
- Neutrophils

In tissues
- Macrophages
- Dendritic cells

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24
Q

What happens at sites of inflammation which results in extravasation occuring

A

Macrophage releases TNF when it needs help
- coats endothelial cells, makes them sticky

neutrophils roll on these sticky endothlelial cells
- when neutrophil hits chemokines present on endothelial surface it becomes activated
- firm attachment bonds form due to intergin
- chemokine gradient causes extravasation

  • helps macrophage
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25
What occurs when sensing non-self
Pattern recognition receptors (PRRs) recognise Pathogen associated molecular patterns (PAMPs) on bacteria - Lectin to recognise sugars, scavenger receptors for identifying lipids on bacteria Multiple ways for leukocytes to bind to bacteria Phagocytes engulf - Proteolytic degradation - forms a phagolysosome Some fragments of bacterial peptide gets combined with MHC to present the antigen on the phagocyte surface Macrophages can take in around 50 microbes at a time
26
Why is adaptive immunity necessary?
Microbes can evade innate immunity - Decoy proteins - some bacteria can live within macrophages * Intracellular viruses and bacteria can hide from innate immunity
27
What occurs in cell mediated immunity
- Cells connect with each other to activate each other - Requires intimate cell contact * antigen presenting cells connect to T cells * T cells connect to B cells
28
What substance does cell-mediated immunity require
Major histocompatibilty complex (MHC) - is the thing that allows cells to present antigens
29
Characteristics of MHC
Class I - Intracellular antigen presentation (EG with viruses) - Present in all cells - Leads to activation of Cytotoxic T cells * Kill infected cell Class II - Extracellular antigens - Result from phagocytosis - Only found on antigen presenting cells - Leads to T helper cells * Help B cells make antibodies to an extracellular pathogen (class II are the ones you think of with typical antigen presentation after phagocytosis, class I is intracellular and helps activate cytotoxic t cells)
30
Process of cell mediated immunity
Phagocytic cells present antigens via the Major Histocompatibility complex (class II) T cell receptors recognise and bind to the Major Histocompatibility complex, and the antigen it is associated with Leads to: - Division - Differentiation - Effector Functions - Memory
31
Stages of T cell activation
Starts with naive t helper cells - becomes activated - CD8 cells (when combined with MHCI/peptide) become Cytotoxic T cells (Tc) * these release perforins and granulysin and directly kill cells - CD4 cells: * in the presence of high levels of IL-12 - becomes Th1 helper cells ** makes macrophages more active and helps kill intracellular pathogens * at a modereate level of stimulation (by IL-12?) - becomes Th2 helper cells ** activates B cells ** Helps antibody production in humoral response
32
What is humoral immunity. Explain the process which occurs.
The immune response that occurs from the activation of B cells Process of activation: - B cells identify antigens via binding to their membrane-bound antibodies - B cells present this antigen on MHC II - Th2 cells (primed by binding to antigen-presenting cells) bind to B cells presenting the specific antigen - Th2 secrete cytokines - Triggers B cells to clonally expand and differentiate - Differentiate into: * Plasma cells * B memory cells
33
What are characteristics of B cells
B cells express membrane-bound Immunoglobulin (IgM or IgD) Each B cell can make 1 antibody type – specific to one epitope of an antigen (epitope is the specific site where the antibody can bind) Born with all possible antibodies complementary to every possible epitope Anti-self antibodies (antibodies that react to anything that is self) are killed during development
34
What is an epitope
The specific site on an antigen where an antibody can bind
35
What type of PRRs are there
Secreted and circulating PRRs Cell associated PRRs (more traditional receptors)
36
What do PRRs (pattern recognition receptors) do
They recognise patterns that are typically associated with non-self Examples: - LPS (lipopolysaccharides) - gram-positive/gram-negative bacteria - dsRNA - CpG motifs
37
Types of secreted and circulating PRRs
* Antimicrobial peptides secreted in lining fluids, from epithelia, and phagocytes. * Defensins, cathelicidin * Lectins and collectins: carbohydrate-containing proteins that bind carbohydrates or lipids in microbe walls. Activate complement, improve phagocytosis. Surfactant is also involved * Mannose binding lectin (deficiency syndromes), surfactant proteins A and D E.g. Pentraxins. Proteins like CRP (non-specifc marker of infection - used to recognise clinically - has some antimicrobial action) can react with the C protein of pneumococci, activate complement, and promote phagocytosis.
38
Cell associated PRRs
* Receptors that are present on the cell membrane or in the cytosol of the cells. * Recognise a broad range of molecular patterns TLRs are main family Activate proinflammatory pathway Interferon for dealing with viruses
39
Membrane bound PPRs
* Family of receptors that may participate in pathogen recognition and particularly in pathogen phagocytosis, the C-type Lectin receptors * Mannose receptor on macrophages (fungi). * Dectin-1, Dectin-2. Widespread on phagocytes, helps recognise beta glucans in fungal walls. Scavenger receptors on macrophages (non-specific)
40
Examples of intracellular pathogens
* Viruses multiply in the cytoplasm of cells * Bacteria such as Salmonella burst out from the phagolysosome and multiply in the cytoplasm of macrophages
41
What are giant cells
Large multinucleated cells formed by fusion of various cells like macrophages, epithelioid cells, monocytes etc. Found at site of chronic inflammation/oother granulomatous conditions
42
Primary Lymphoid organs
Bone marrow - origin site Thymus - T cell maturation site
43
Secondary lymphoid organs
Lymph nodes - site of dendritic cell, B and T-cell interactions Spleen - removes RBCs and Ab-coated bacteria Muscosal associated lymphoid tissues e.g. GUT ASSOCIATED LYMPHOD TISSUE (GALT) - has most plasma cells in body * includes PAYER'S PATCHES
44
Tertiary lymphoid organs (TLOs)
Transient germinal centres Usually ectopic lymph node-like structures formed during chronic infection, GvHD, autoimmunity. - e.g. in MS, TLOs form in brain - produce anti-myelin antibody -> demyelination
45
What occurs at lymph nodes
Dendritic cells enter via afferent lymphatics - present Ag to naive CD4 cells in PARACORTEX. -> become effector cells or memory cells - cells exit via efferent Site of interaction between innate and adaptive cells
46
What do lymphoid follicles (like Peyer's patches) mainly consist of
B cells
47
Diff parts of the spleen and their function
Red pulp - mechanical filtration of RBCs White pulp - active immune responses through humoral/cell-mediated. * Primary follicle - rich in B cells * Marginal zone * Periateriolar lymphoid sheath (PALS) - rich in T cells Also stores RBCs, lymphocytes etc - can be released in hypovolaemia/-oxia - and clear old plts from circulation
48
Types of PRRs
Membrane bound - Toll-like Receptors (TLRs) - C-type Lectin Receptors (CLRs) Cytoplasmic - NOD-like receptors - RIG-I-like receptors
49
What are PRRs and what do they do
Germline encoded Pattern Recognition Receptors (evolutionary conservation) Detects Pathogen-Associated Molecular Patterns (PAMPS) and Damage Associate Molecular Patterns (DAMPS)
50
Types of TLRs
Typically: - TLRs detecting genetic material are located on ENDOSOME WITHIN CELLS - TLRs detecting other bacterial material - CELL SURFACE TLR 5 - Five for Flagellin (flagellated bacteria) ** TLR 2 - detectes LIPOTEICHOIC ACID (peptidoglycan wall of gram +ve) - Two for TB - DETECTS MYCOBACTERIA ** TLR 4 - LPS on G-ve TLR 9 - Nine for Non-methylated CpG (cytosine-guanine) - found in bacterial/viral DNA TLR 3/7/8 - viral RNA
51
NOD 1/2 function
activate NF-kB pathway -> APOPTOSIS activated via CARD domains on NODs
52
Function of dendritic cell
Phagocytic PROFESSIONAL ANTIGEN PRESENTING CELL (MHC II) - can even CROSS-PRESENT
53
Which chemokine receptor guides DCs to secondary lymph organs
CCR7
54
Differences in function of Dendritic cells once mature
Increased Co-stimulatory molecules INCREASED MHC II expression INCREASED secretion of PRO-INFLAM CYTOKINES INCREASED CCR7 expression Increased Glycolysis DECREASED PHAGOCYTIC capacity
55
How do plasmacytoid dendritic cells repond to viral infection
Release IFN alpha and beta
56
Which interleukin is particularly associated with acute inflammation
IL-8 - attracts Neutrophils!!
57
Major components of neutrophil phagolysosme
ALPHA-DEFENSINS LACTOFERRIN
58
What is resp burst? What happens in resp burst
Killing mechanism of neutrophils (oxygen dependant) - Electrons pumped into phagolysosome by NADPH OXIDASE - Combine with O2 to make SUPRAOXIDE IONS - ions combine with PROTONS to make PEROXIDE (bacteriacidal) - peroxide can also be CHLORINATED by MYELOPEROXIDASE to make HYPOHALOUS ACID (bactericidal)
59
Process of neutrophil extravasation
1. E-selectin (an adhesion molecule on the capillary endothelium), is activated by IL-1 and TNF-α from damaged cells and binds to the glycoprotein CD15 on neutrophils in blood. 2. This causes neutrophils in the blood to slow down and roll along the endothelium lining. 3. ICAM-1 on endothelium (induced by LPS, IL-1, TNF-α) binds to integrin on neutrophil; the neutrophil stops. 4. Diapedesis: neutrophil squeezes through endothelium (holes caused by C3a, C5a, chemokines, histamines, prostaglandins, leukotrienes (causing smooth muscle contractions in the bronchioles))
60
How do eosinophils deal with parasitic infections
Release CATIONIC GRANULES (e.g. MAJOR BASIC PROTEIN) Release ROS (eicosanoids, leukotrienes, elastase among other molecules)
61
Function of mast cells. Site. And relation to Ig?
Plays important role in ALLERGIC reactions + PARASITIC infections - MAIN source of HISTAMINE Found in MUCOSAL SURFACES IgE binds to antigens and presents Fc region to activate mast cells
62
What do activated mast cells release and what do those substances do
HISTAMINE - increase VASC PERMIABILITY - SMOOTH muscle CONTRACTION Cytkines: - !L4, IL13 - promotes Th2 DIFF and IgE PRODUCtion - TNFa - TISSUE INFLAMMATION Lipid Mediators Leukotrines PROSTAGLANDINS - collectively -> vasc perm, SM contract, MUCUS secretion, are CHEMOATTRACTANTS
63
What is required for cells to develop in into mast cells
Stem cell factor (a cyotkine + growth factor)
64
What is Antibody-dependant Cellular Cytotoxicity. What occurs in ADCC?
Independant mechanism that does not require complement and uses only 1 CELL TYPE (typically NAT KILLER CELLS) (Typically) IgG binds to SURFACE ANTIGENS on infected/cancerous cells (or VIRAL PROTEINS during VIRAL REPLICATION). NK have CD16 Fc receptors and CROSS-LINK with antibody Fc region. - triggers DEGRANULATION of LYTIC agents -> CELL APOPTOSIS
65
What do NK cell lytic granules contain
PERFORIN and granzymes - induce apoptosis + cell lysis
66
How do NK cells differentiate between self and non-self
By PRESENCE of MHC 1 - CANCER cells typically DOWNREGULATE MHC 1 NK has INHIBITORY RECEPTORS activated by MHC I. If not enough MHC present - NK activate + try to kill cell
67
What stimulates cytotoxic T cells to attack tumour cells
The cytokines produced by NK cells (also specifically they kill cells with endogenous antigens)
68
Which cells are professional antigen presenting cells
Macrophages B-cells Dendritic cells (most potent - go to 2ndry organs - aid adaptive response)
69
What do professional APCs do
Present EXOGENOUS Ag in context of MHC-II - processed in ER
70
How are endogenous proteins presented? By which cells?
Present in CYTOSOL (e.g. viral/cancer-related) - processed in ENDOSOMES Presented in context of MHC I - found in ALL CELLS (EXCEPT RBCs)
71
How do dendritic cells activate Tc cells
CROSS-PRESENTATION - present EXOGENOUS antigens on MHC 1
72
What is an immune synapse
When immune cells bind together
73
What 3 things are essential for a response to occur at an immune synapse
1. Binding of PRIMARY RECEPTORS (e.g. MHC II to TCR on t cells) 2. Binding of CO-STIMULATORY MOLECULES (e.g. CD80 to CTLA4 - don't need to know name detail) 3. A robust release of APPROPRIATE CYTOKINES
74
What happens if MHC binding to another immune cell occurs without any other stimulation
ANERGY - lack of response - form of PERIPHERAL TOLERENCE
75
What is the identifying co-stim molecule for all T cells. What is its main function
CD3 (protein complex - 1 gamma, 1 theta, 2 epsilon chains - probs don't need this much detail) Intracellular signelling -> activates T cell
76
What co-stim type cells do T cells initaly start as? What do they change to in the thymus?
Initially NAIVE CD4+CD8+ double pos cells (have both). Undergo THYMIC EDUCATION so they only have EITHER one or the other. Also undergo VDJ recombination (also does same for Fab regions on Ab) to determine which EPITOPE their TCR (t cell receptor) will recognise - super specific to a certain antigen
77
Which antigens are an exception the very specific nature of TCRs
SUPERANTIGENS - bind to alpha/beta chains of any TCR - activates ~20% of T cell population (big response)
78
What is a naive lymphocytes
Never encountered antigen
79
How can Naive and Memory T cells be differentiated
nAive - has CD45RA memOry - has CD45RO
80
\what is the general marker for T cell activation
CD25 expression
81
What are the 2 mechanisms by which Tc (CD8+) cells kill
1. PERFORIN and GRANZYMES 2. express *Fas* LIGAND - binds to Fas on target cells -> activates CASPASE CASCADE -> APOPTOSIS
82
Perforin
PORE forming CYTOLYTIC protein - alows SALT + WATER to enter cells -> CELL LYSIS
83
What are granzymes and what do they do?
Serine proteases - CLEAVE CASPASE PROTEIN (CPP-32) -> ACTIVATE a NUCLEASE (CAD) -> initiates DNA DEGRADATION + APOPTOSIS
84
Th1 vs Th2
Th1 CELL-MEDIATED; Th2 HUMORAL Th1 regulate MONOCYTES/MACROPHAGES, Tc, NK - eliminate cellular antigens Th2 regulate EOSINOPHILS, BASOPHILS, MAST CELLS, B CELLS - increased IgE and IgG they are ANTAGONISTIC to each other - T CELL POLARISATION
85
Types of T helper cells (CD4+)
Treg (regulatory cells) Th17
86
Treg vs Th17 cells
Treg - PERIPHERAL IMMUNE TOLERANCE; Th17 - MUCOSAL MEMBRANE (stimulates INFLAMMATION) Treg - principle cytokine = IL10 (mass ANTI-INFLAM action) Th17 - IL17 (induces INNATE cells to make IL8 -> stimulates NEUTROPHIL production/recruitment)
87
Which cytokine maintains Th17 populations
IL-23 (target for biologics)
88
How can B cells be activated? What kind of response does each produce?
1. Th2 cells - produce LONG-LIVED plasma cells * typically make IgG, E or A+ 2. Can be activated directly by ANTIGEN in absence of T cell help - makes SHORT-LIVED plasma cells (+ response) * typically these plasma cells have LESS AFFINITY and produce IgM
89
What are the marker and the co-stimulatory molecule associated with mature B cells
Marker - CD20 Co-stim - CD19
90
What processes do B cells undergo upon activation and where does activation occur
SOMATIC HYPERMUTATION and AFFINITY SELECTION (aided by dendritic + t cells) - mainly in CORTEX OF LYMPH NODES
91
What occurs in somatic hypermutation and affinity selection
somatic hypermutation: - activation-induced cysteine deaminase (AID) introduces RANDOM MUTATIONS in Fab Ab region gene Affinity selection: - Dendritic cells present same antigen (testing AVIDITY) - less avidity - neg selected - greater avidity = Positively selected -> undergo CLASS SWITCHING and clonal proliferation
92
What happens when B cells are activated in lymphoid follicles
They develop into germinal centres
93
Where does complement bind during opsonisation
Fc region of antibody
94
Which antibodies are in colostrum
IgA, M and G - but IgA is principle
95
Which cell type raised in bacterial infection
Neutrophils (esp if pyogenic)
96
Which cell type raised in viral infections
Lymphoctes (also raised in intracellular bacterial infections e.g. TB and some protozoa e.g. Toxoplasma)
97
Define hypersensitivity
Undesirable response to antigenic, allergenic or self material. This requires a pre-sensitized state of the host
98
Types of hypersensitivity reactions
Type 1 - Anaphylactic Type 2 - Cell bound Type 3 - Immune complex Type 4 - Delayed Hypersensitivity Type 5 - Ab interferes with ligand binding (uncommon)
99
Type 1 hypersensitivity reaction
FAST - within minuites CROSS-LINKING of ANTIGEN to IgE on MAST CELLS + BASOPHILS -> massive DEGRANULATION -> massive HISTAMINE RELEASE ** IL4 - KEY CYTOKINE - causes class switching to IgE, Th2 Polerisation ANAPHYLAXIS + ATOPY (asthma, eczema)
100
Type 2 hypersensitivity reaction
IgG/IgM binds to SELF ANTIGEN -> CELL DESTRUCTION by membrane attack complex + cell mechanisma AUTOIMMUNE
101
Type 3 hypersensitivity reaction
IgG BINDS SOLUBLE ANTIGEN (free antigen + antibody combine) -> circulating IMMUNE COMPLEX - DEPOSIT in vessel walls esp in KIDNEYS -> inflam response - RBCs with COMPLEMENT RECEPTOR 1 bind to complement coated immune complexes and transport them to the liver and spleen for phagocytosis. E.g. - SLE - post-strp glomerular nephritis
102
Type 4 hypersensitivity reaction
Th1 mediated - ACTIVATED BY APCs -> forms memory T cells -> when reactivated -> activate macrophages -> tissue damage E.g. - TB - GvHD -MS - Guillain-Barre syndrome
103
Type 5 hypersesitivity reaction
IgM/IgG bind to CELL SURFACE RECEPTORS -> BLOCKS or STIMULATES ENDOGENOUS LIGAND BINDING e.g. - Graves - Myasthenia gravis
104
Main ways autoimmunity can develop
- Incorrect THYMIC education - Tregs - CD4 activation against AUTOANTIGEN
105
Features of autoimmunity
- Often relapsing-remitting - Organ-specific vs Systemic - Damage to or destruction of tissues - Altered organ growth/function - Generation of autoantibodies
106
What is the defining factor for developing AIDS
< 200 cells/uL of CD4 cells
107
Which cytokine is the main activator of macrophages
IFN gamma
108
What triggers classical complement pathway
Antibodies
109
What triggers lectin pathway of complement system
when MANNOSE BINDING LECTIN (MBL - a protein which binds mannose sugars on pathogen surfaces) binds to mannose on bacteria triggers cascade response

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