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B cell primary immunodeficiencies
Fichas del conjunto (21)
- 1Which genetic event is involved in the aetiology of x-linked agammaglobulinaemia?A mutation in Bruton's tyrosine kinase (BTK) gene.
- 2What effect does the genetic event in x-linked agammaglobulinaemia have on B cells?The BTK mutation results in pre-B cells failing to differentiate into mature B cells.
- 3What is the inheritance pattern of XLA?It is X-linked recessive, so it is predominately seen in males as they only have 1 copy of the X chromosome and therefore cannot use X-inactivation as females can. This pattern is used in the diagnostic differentiation between XLA, CVID, and Hyper IgM syndrome.
- 4How does XLA present clinically?As frequent and recurrent infections (otitis, sinusitis, pneumonia) - noticed in the first 5 years of life as the condition is genetic.
- 5How is XLA diagnosed?Blood screening identifying low serum IgG, IgA, and IgM (2 or more S.D. below the normal value for the individual's age) and low (<2%) CD19+ B cells in the peripheral blood is diagnostic of XLA, along with the inheritance pattern and infection history.
- 6How is XLA treated?Lifelong immunoglobulin replacement therapy (IRT), antibiotic courses for infections (potentially long term), and no vaccinations as IgG and IgM responses cannot be developed against the pathogens.
- 7What genetic event results in common variable immunodeficiency (CVID)?Mutations in the TACI alleles - the variations in the mutations result in the varied phenotypes seen, as there are 30-40 conditions under the CVID 'umbrella'.
- 8What does the genetic event causing CVID do to B cells?Mature B cells fail to differentiate into plasma cells and class switch.
- 9How does CVID present clinically?Frequent and recurrent viral/bacterial/fungal/protozoal infections, especially upper respiratory tract infections, and autoimmunity and allergies develop in ~20% of patients. This can include gastrointestinal disorders such as irritable bowel disease.
- 10How is CVID diagnosed?Blood screening reveals low serum IgG, IgM, and IgA, and there is a familial history of the disease affecting both males and females, unless the mutation is spontaneous.
- 11How is CVID treated?Lifelong immunoglobulin replacement therapy and antibiotic courses when necessary.
- 12What is the cause of IgA deficiency?The aetiology is unknown, but the result is that mature IgA B cells are unable to differentiate into plasma cells and secrete IgA.
- 13How does IgA deficiency present clinically?As frequent and recurrent urogenital, respiratory, and gastrointestinal infections, chronic diarrhoea, allergies and autoimmunity. The autoimmunity usually results in circulating levels of auto-organ antibodies being high, resulting in type 3 hypersensitivity reactions. Further, anti-IgA may be produced, resulting in transfusion reactions on receipt of blood products. Some patients may be asymptomatic as IgM 'compensates' for IgA.
- 14How is IgA deficiency diagnosed?Blood screens reveal low serum IgA (<7mg/dL) but normal levels of other immunoglobulins.
- 15How is IgA deficiency treated?There is no IgA replacement therapy available so long term courses of antibiotics are prescribed to treat the recurrent + frequent infections.
- 16What mutation(s) result in Hyper IgM Syndrome?Hyper IgM Syndrome can result from either a mutation in the B cell activation-induced cytidine-deaminase enzyme which occurs in both males and females, or from a mutation in the CD40 ligand on B cells, which is X-linked and thus predominately occurs in males.
- 17What effect do the mutations in Hyper IgM Syndrome have on B cells?Mature B cells are unable to class switch so only IgM is produced.
- 18How does Hyper IgM Syndrome present clinically?As recurrent sinopulmonary infections, and pneumonia caused by Pneumocystis carnii. Associated abnormalities include neutropenia and aplastic anaemia.
- 19How is Hyper IgM Syndrome diagnosed?Blood screens reveal low IgG/IgA/IgE but >200mg/dL IgM. The ultimate cause of it may be identified by analysing the inheritance pattern within a family.
- 20What is the treatment for Hyper IgM Syndrome?Lifelong immunoglobulin replacement therapy and antibiotic courses whenever these are necessary.
- 21Why might XLA be masked for the first 6 months of life?Because maternal antibodies delivered through the placenta protect the baby for this length of time.
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- From the 07-02-14 Immunology and Disease lecture.
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- sophietevans
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