Immuno 4: Primary Immune Deficiencies 2 Flashcards
What is the most common form of SCID ?
X-linked SCID
Which cells are affected in X-linked SCID and why ?
Reduction in T and NK cells
Increase in premature B cells
Because Common gamma chain is mutated which is an important component of Cytokine receptors. Therefore cant respond to cytokines causing early cell arrest in T and NK cells. No IgA or IgG because CD4+ Th cells needed for Isotype switching.
Which cells are affected in ADA deficiency SCID and why ?
Low T, NK and B cells
Adenosine deaminase enzyme is deficient which causes failure of lymphocyte maturation
Why are infants with SCID protected in the first 3 months ?
maternal IgG is still present in the infants circulation and provides immunity
What is the function of CD4+ T cells in the immune response ?
- activates B cells
- activates CD8+ cytotoxic T cells
Which genetic syndrome causes the thymus to be underdeveloped and therefore a reduced number of T cells in children?
DiGeorge syndrome
T cell numbers recover with age
List 4 pathologies of DiGeorge syndrome ?
CATCH 22
Cardiac abnormalities ( Tetralogy of fallot)
Abnormal facies (low set ears, high forehead)
Thymic aplasia (Reduced T cells)
Cleft palate
Hypocalcaemia (hypoparathyroidism)
22nd chromosome mutation 22q11
(There is developmental defect in the pharyngeal pouch)
What causes a profound deficiency in CD4+ T cells but normal numbers of CD8+ T cells ?
What is the name of this syndrome ?
Absent expression of MHC class II molecules. (Means that T cells cant undergo affinity selection in the thymus to become CD4+)
Bare Lymphocyte syndrome -Type 2 (BLS type 2)
Why do you get a reduction/absence in IgG and IgA immunoglobulins with CD4+ T cell defficiency (e.g in BLS type2) ?
The CD4+ T helper cells are involved in B cell Isotope switching so you have IgM B cells but cant switch to IgG/ IgA in the germinal centres.
What is the definitive treatment of SCID and BLS type 2 ?
Haematopoeitic stem cell transplant
How do you treat ADA SCID ?
Enzyme replacement therapy
Which bacterial infection are patients with an IFN gamma deficiency particularly susceptible to ?
Recurrent Mycobacterium Marinum infections (atypical mycobacterium)
22q 11.2 deletion syndrome is also known as ???
DiGeorge syndrome
Defect in the development of the pharyngeal pouch
Is the IgM B cell response T cell dependent ?
No
How do CD4+ T cells help B cells undergo B cell differentiation ?
CD40 ligand is expressed on CD4+ Th cells and this acts on CD40 receptors on B cells causing isotope switching.