Week 3 - Antibiotics Flashcards
Familiarise with the scenario
Ambrose is a 2 years 3 months old boy who is attending a follow-up appointment with his paediatrician at Great Ormond Street Hospital to receive the results of his recent tests. He had been referred by his GP after repeated infections that started around 8 months of age. His mother reported that Ambrose had been breast fed for the first 6 months, and until 8 months he had been a bright and active child. Subsequently, he developed his first case of pneumonia, then over the next 12 months had five episodes of otitis media, several sinus infections, a single episode of erysipelas on his cheek, plus two further bouts of pneumonia - all the infections were successfully treated by antibiotics. He also seemed to have recurrent episodes of diarrhoea. Ambrose’s mother was concerned that he seemed to be constantly on antibiotics.
At the first appointment the paediatrician took a medical family history where Ambrose’s mother reported that;
· She had grown up in Sierra Leone.
· That she had a younger brother who had died from pneumonia when he was 2 years old.
· Ambrose’s grandmother is alive in Sierra Leone with no serious health problems.
· She has a sister who is alive and well, who has a healthy son and daughter.
· Ambrose has a healthy younger sister.
· There is no significant family history of any disease on Ambrose’s father’s side.
The paediatrician examined Ambrose and found that he had no visible tonsils, and ordered a full blood count and immunoglobulin profile to analyse the levels of immunoglobulins in Ambrose’s serum. The blood tests showed he had a normal white blood cell count (5000 cells/µl). The white blood cell differential and immunoglobulin profile were as follows:
More detailed laboratory studies using flow cytometry it was found that:
· 85% of his blood lymphocytes bound an antibody to CD3, a pan-T cell marker (normal).
· 55% were helper T cells reacting with an anti-CD4 antibody (normal).
· 29% were cytotoxic T cells reacting with an anti-CD8 antibody (normal).
· None of Ambrose’s blood lymphocytes bound an antibody against the B cell marker CD19 (normal = 12%).
· T cell proliferation indices in response to phytohemagglutinin, concanavalin A, tetanus toxoid, and diphtheria toxoid were 162, 104, 10, and 8, respectively (all normal).
The paediatrician considers that Ambrose might have some type of immunodeficiency and suggests that he begin a course of intravenous immunoglobulins.
What does otitis media mean?
An ear infection
What does erysipelas mean?
Cheek rash
What are the general types of immunity? What cells are involved in each?
Innate immunity which is non discriminative - - includes physical and chemical barriers such as the mucosal linings of our respiratory tract and GI tract
- macrophages which come from monocytes and secrete cytokines
- neutrophils, eosinophils, basophils
- natural killer cells
Adaptive immunity
- acquired
- small lymphocytes which include T cells and B cells (incl plasma cells)
How do macrophages work?
What do they recognise? What do they bind to? What do they secrete? What signalling cascade occurs? What is the general name of the immune response they are a part of?
Macrophages recognise bacterial or viral components such as lipopolysaccharides (LPS) or double stranded RNA (dsRNA)
via special receptors called Toll-like receptors
When TLR activation happens because they have bound to the above, this causes macrophages to secret cytokines (small molecules involved in cell signalling and attraction) AND phagocytise infected cells
The innate immune system then activates the adaptive immune system (B cells and T cells etc)
Explain generally how acquired immunity works
Mediated by lymphocytes which are either T cells or B cells
B cells secrete antibodies that bind to antigens which are proteins on the surface of cells or free floating in the body.
When an antibody binds, it triggers mechanisms that will attack and destroy infected cells.
Some B cells become memory cells
T cells can either be T helper cells or cytotoxic
Briefly explain how antibodies help prevent bacterial infections?
4 marks
Antibody is critical for defence against pathogens, especially extracellular bacteria:
· it binds to them to increase their uptake by phagocytes (for example, macrophages or neutrophils),
· or to induce their killing by complement activation
· or by cellular components of the immune system (antibody dependent cellular cytotoxicity, ADCC).
· In addition, antibody can block infection by preventing the binding of pathogens to critical receptors on host cells and can neutralise the activity of toxins that cause disease.
Explain generally how acquired immunity works
B cells secrete antibodies that bind to antigens which are proteins on the surface of cells or free floating in the body
When an antibody binds, it triggers mechanisms that will attac and destroy infected cells
Some B cells become memory cells
T cells can either be T helper cells or cytotoxic T cells
Explain why Ambrose was healthy for the first 8-9 months of his life?
2 marks
The passive transfer of IgG across the placenta protected him plus (1 mark)
the fact that he was breast fed again protected him for the 1st 8 months. (1 mark)
From the family history of Ambrose what is the inheritance pattern and justify your answer
4 marks
· X-linked recessive (1 mark ½ mark for x-linked only)
· Only boys affected (Ambrose and the uncle) (1 mark)
· Ambrose’s mother is a carrier she has 2 X chromosomes the affected chromosome is transferred to Ambrose (1 mark) but even if his sister has this affected chromosome she does not have the condition so its recessive (1 mark)
Which Cohn fraction contains the gammaglobulins that are used in the treatment of Ambrose?
1 mark
Cohn fraction II
What condition does Ambrose have?
X linked agammaglobulinaemia
What is wrong with Ambrose’s immune system?
The B cells (acquired immunity - humoral) is not working properly
So the lymphocytes are present but are not mature and do not become plasma cells or memory cells
T cells and innate immunity is working fine
What are the components of the innate immune system?
Physical, chemical barriers Phagocytic leukocytes Dendritic cells Natural Killer Cells Plasma proteins (complement)
What are the components of the adaptive immune system?
Humoral immunity (B cells, which mature into antibody secreting plasma cells)
Cell-mediated immunity (T cells maturing into either hyper cells or cytotoxic T cells)
When is the innate immune system active?
Always
When is the acquired immune system active?
Normally silent
Only when triggered
Describe the response and potency of the innate immune system
Immediate response
Limited and lower potency
Describe the response and potency of the acquired immune system
Slower to respond
Over 1-2 weeks but is much more potent
Describe the specificity of the innate immune system
General
Recognised many classes of pathogens (bacteria, viruses, fungi, parasites) but cannot make fine distinctions
Describe the specificity of the acquired immune system
Recognises highly specific antigens
Describe the course of the innate immune system
Attempts to immediately destroy the pathogen, if it can’t it recruits the acquired immune system and contains it until it arrives
Describe the course of the acquired immune system
Slow to respond
Effector cells usually produced after 1 week
Entire response 1-2 weeks
Varies between individuals
Does the innate immune system have memory cells?
Nope
Reacts with equal potency upon repeated exposure to the same pathogen
Does the acquired immune system have memory cells?
Yes
Remembers specific pathogens
When re-exposed, the cells are produced much faster and more potent the second time around
What is the story behind Ambrose always being on antibiotics?
He has never produced any antibodies and the humoral immunity never worked but because he was being breast-fed, he was getting IgA from the breast milk and so wasn’t unwell, but as time went on he stopped breastfeeding and the IgA finished and so he started ‘always being on antibiotics’
Where IgA found and secreted?
What does IgA do?
Found in saliva, tears and breast milk
Mucosal areas such as gut, respiratory tract and urogenital tract
Protects against pathogens
Where IgD found and secreted?
What does IgD do?
Part of the B cell receptor
Activate basophils and mast cells to produce antimicrobial factors
Where IgE found and secreted?
What does IgE do?
Responsible for allergic reactions
(Binds to allergens and triggers histamine release from mast cells and basophils, involved in allergy)
Protects against parasitic worms
Where IgG found and secreted?
What does IgG do?
Secreted by plasma cells in the blood
Able to cross the placenta into the foetus (only one)
Provides the majority of antibody based immunity against invading pathogens
Where IgM found and secreted?
What does IgM do?
Can be attached to the surface of a B cell or secreted into the blood
Responsible for early stages of immunity
____________________
On the surface of B cells (monomer) and in a secreted form (pentamer) with very high avidity (strong binding between antibody and antigen)
Eliminates pathogens in early stages of B cell mediated (humeral) immunity before there is sufficient IgG
Which antibodies are monomers?
IgD, IgE, IgG
Which antibodies are dimers?
IgA
Which antibodies are pentamers?
IgM
What do antibodies do?
Antibody mediated cell cytotoxicity (kill cells)
Phagocytosis
Opsonization
Virus neutralisation
Receptors internalization
Crosstalk with receptor signalling
Activation of complement
Which antibody can cross the placenta?
IgG
Which antibody levels are high before birth in a foetus?
Maternal IgG is passively transferred through the placenta peaking just before birth
IgM starts to rise 3 months before birth and reaches its peak 1 year after birth
When are IgG levels transiently low and why?
Just after birth IgG levels are transiently low as just before birth IgG levels are maternal transferred, just after birth the baby starts to produce its own IgG
What is the relationship between the neonatal Fc receptor and IgG?
The Neonatal Constant Chain receptors make the IgG last longer than they normally do from the mother to the neonate
Can you explain Ambrose’s test results?
Neutrophils 45% (45-74%)
Lymphocytes 43% (16-45%)
Monocytes 10% (3-7%)
Eosinophils 2% (0-2%)
IgG 80 mg/dL (600-1500mg/dL)
IgA not detected (50-125mg/dL)
IgM 10mg/dL (150mg/dL)
Innate immune system (neutrophils, eosinophils, monocytes) is within normal range, T cells are working fine (lymphocytes)
Adaptive immune system is not functioning properly, all forms of antibodies are reduced and below the normal range
How common is X linked agammaglobulinemia?
Approx 1:100,000 to 1:300,000
Extremely rare in females (mother carrier, father has the condition)
What is the life expectancy of X-linked agammaglobulinemia?
40 years
What infections do patients with X linked agammaglobulinemia often get?
History of recurrent infections
Mostly in the respiratory tract
Particularly encapsulated pyogenic (pus producing) bacteria as these often need opsonisation to get rid of them (Haemophilus influenza and Pseudomonas species)
Skin infections are mostly caused by group A streptococci and Staph. aureus
What is the family history of X-linked agammaglobulinemia in Ambrose’s family?
Grandma carrier
Uncle had the condition and died young
Mother carrier
Ambrose has the condition (boy)
How do you diagnose X-linked agammaglobulinemia?
Blood tests that show a complete lack of circulating B cells (determined by B cell marker CD19 and/or CD20) and low levels of all antibody classes
In what gene is there a mutation that causes X-linked gammaglobulinemia?
BTK gene
Bruton’s tyrosine kinase gene
On the X chromosome
Name the cascade from mutation to defects in humoral immunity seen in X-linked agammaglobulinemia
Mutation in BTK gene on X chromosome
Impaired function of BTK gene, a signal transduction protein involved in B cell maturation
Decreased Phospholipase C signalling downstream of BTK
Impaired maturation of B cells from precursor cells (leading to low numbers of B cells in the blood, bone marrow and peripheral lymphoid tissues - leading to absence of mature B cells CD19+ and plasma cells in blood and bone marrow and absence of tonsils, adenoids, lymph nodes)
Impaired B cell function
Inability to produce all classes of immunoglobulin proteins (antibodies) (leading to not being able to recognise antigens - leading to:
- increased susceptibility to infection esp bacteria
- decreased detectable levels IgA, IgG, IgM
- decreased detectable antibodies in response to immunisations and common antigens
What happens in children with DiGeorge syndrome?
T cell maturation and problems with the thymus
Cell-mediated immunity is affected
Features look different and problems with immunity
What enzyme is defective in children with agammaglobulinaemia? What is the effect?
Bruton tyrosine kinase
Impairment of B cell maturation
Patients have normal levels of pre-B cell populations but problem with maturation
What is the pathway of B cell maturation?
What antigens or antibodies are present on the surface at each stage?
Stem Cell (in bone marrow) CD34+
Pro B cell
CD24+, CD40
Immature B cell
CD19+, CD24+, CD40
IgM on surface
Mature B cell
CD19, CD24, CD40
IgM and IgD on surface
Either Memory B cell (CD19, CD24, CD40 - IgM, IgE or IgM on surface) or plasma cell (secrete IgM, IgA, IgE or IgM)
What vaccines can children with X-linked agammaglobulinaemia have?
Inactivated vaccines - normal dendritic and T cell responses
Cannot take live viral vaccines (e.g measles, mumps, rubella)
What is the treatment for children with X-linked agammaglobulinaemia?
Replace immunoglobulins
- intravenous infusion 3-4 weekly for life (later in life can be in port in skin - later may be able to do it subcutaneously)
- Maintain IgG level at 600mg/dL
- Disaggregated IgG before use - otherwise will get fevers and chills (disaggregated means that the immunoglobulins should be treated)
And aggressive treatment with antibiotics to prevent bacterial infections that may cause long-term complications (e.g. ear infection and hearing and resp tract etc)
In X-linked agammaglobulinemia, lower B cell numbers in the blood, bone marrow and peripheral lymphoid tissues leads to
Absence of mature B cells (CD19+) and plasma cells in the blood and bone marrow
Absence of tonsils, adenoids, +/- lymph nodes
In X-linked agammaglobulinemia, exposure of androgens fails to generate antibodies from B cells, what does this lead to ?
Increased susceptibility to infection especially bacterial infections (e.g. pneumonia)
Decreased or undetectable levels of IgA, IgG and IgM
Decreased or undetectable antibodies i response to immunisations and common antigens
What is herd immunity?
90% children plus have been vaccinated to avoid the transmittance of infections in a crowd
X linked agammaglobulinemia children can’t take live vaccines so herd immunity is really important for them
What are Cohn fractions?
A series of purification steps to divide blood plasma into fractions. The process is based on the different solubility of albumin and other plasma proteins based on pH, ethanol, conc, temperature, ionic strength and protein conc
The plasma is pool from 1000 donors so you get antibodies from the bugs that everyone has encountered, but is screened for infectious diseases (HIV, Hep B etc)
It is fractionated using ethanol and temperature
What does Cohn fraction I have in it?
Fibrinogen
What does Cohn fraction II have in it?
Immunoglobulins (mainly IgG)
What does Cohn fraction III have in it?
Immunoglobulins (more IgA and IgM)
What does Cohn fraction V have in it?
Albumin (most soluble so its the last thing to come out)
Which Cohn fractions have immunoglobulins?
II and III
What does Cohn fraction IV have in it?
Alpha globins
What are some differential diagnosis?
Hypogammaglobulinemia (CVID)
X-linked agammaglobulinemia (XLA)
Autosomal-recessive agammaglobulinemia
Severe combined immunodeficiency (SCIDs)
Transient Hypogammaglobulinemia of infancy
Where are B cells produced? Where do they mature?
Don’t know where but then moves to the bone marrow
Mature in the lymph nodes
What is X agammaglobulinemia?
Lack of gamma globulin in the blood plasma causing immune deficiency
People with XLA have very few B cells, specialised white blood cells
More susceptible to infections because their body makes very few antibodies
How common is X agammaglobulinemia?
1 in 190,000 male births
How does the mutation in the BLK gene lead to XLA?
Absence of BTK blocks B cell development which means lack of antibodies
Where is BTK found? What is it?
Xq22.1
A tyrosine kinase
What are the signs and symptoms of X-linked agammaglobulinemia?
- Baby well for the first few months
- Recurrent infections: skin infections, nasal infections, sepsis, pneumonia
- GI infections such as diarrhoea, abdominal pain and poor growth
- Histopathology: Tonsils, spleen, adenoids, peters patches in intestines and lymph nodes where B cells undergo maturation, differentiation and storage are poorly developed
How do you diagnose XLA from clinical history?
Recurrent infections such as otitis media, pneumonitis, sinusitis
Severe life-threatening bacterial infections such as sepsis, meningitis
Paucity (reduced quality) of lymphoid tissue
How do you diagnose XLA from laboratory?
Reduced/no serum immunoglobulin (IgG, IgM, IgA)
Reduced numbers of B lymphocytes (using CD19)
Severe neutropenia
Normal or high levels of monocytes
What is CD19?
A B lymphocyte antigen
What is the prognosis for XLA?
Prognosis: likely course of a medical condition
Early therapeutic measures and treatment compliance are major prognostic factors
Do lead a normal life and can do all activities
Which antibody demonstrates an acute infection and what structure does it have?
IgM
Pentamer
Talk about the process of which antibodies are made in the body?
Foreign body ingested by antigen presenting cell (APC)
APC display the antigen of foreign body onto its surface
Recognised by T cells either from CD8+ and CD4+
T helper cells release cytokines which stimulate B cells that recognise this specific antigen
B cells then mature into plasma cells and release antibodies
How does gene therapy work?
Take a stem cell from original patient
Insert a virus which has been adapted to carry a given gene for example
Allow virus to place gene into a stem cell
Allow these cells to grow and place into patient
Define diarrhoea
Loss of 250g of faeces
3 or more than normal loose stool per day
Persistent for more than 14 days (chronic)
