me007
Forum Guru
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why in IgA deficiency sinusitis, otitis, bronchitis or pneumonias are caused by encapsulated bacteria?
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| new_n_lost
Politically InCorrect
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IgA has two major functions. The first is to cause bacteria and allergic substances to stick to the mucus membranes. The second is to turn on the alternative complement pathway to destroy them. Improper function or secretion of IgA has been implicated in a variety of immune complex disorders including systemic lupus erythematosis and phlebitis.
If there is insufficient IgA in the tissues to bind with microbes or allergic particles, they will pass into the portal circulation and liver. If the liver is incapable of dealing with the immune complexes coming from intestinal absorption, they will pass into the systemic circulation and stimulate a general immune response. Allergic disorders and auto immunity occur with undue frequency in the milder forms of IgA deficiency.
In germinal centers, antigen is presented by follicular dendritic cells with help from CD4+ T cells and stimulates B cells to proliferate and undergo somatic mutation and immunoglobulin class-switching. B cells that produce high antigen affinity antibodies are selected to develop into plasma cells that produce different immunoglobulin isotypes (ie, IgM, IgG, IgA, or IgE) or become recirculating memory B lymphocytes.
Since most of the B- cell sensitization has to be in Encapsulated bacteria and the IgA class is a mucosal Protector therefore in its deficiency the recurrent inf take place. its also being Impliacted in Auto-immune Diseases n Atopic Eczema. For a further detailed mechanism in those 2 areas u might have to search.
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| indidoc1
Forum Guru
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Hmmm.. nnl hs explained it very well above. lemme add whatever little i remember to it..
1-Its not that only encapsulated bacterial infections increase in IgA deficiency.. Chr. diarrhea due to Giardia is also common .. as are other mucosal infestions (which i can't recollect now ) 
2- An explanation fr why infection wth some encapsulated bacteria are more is that some of those .. like H.influenzae and S.pneumoniae have IgA proteases, which further decrease the deficient mucosal IgA .
3-Also, as nnl said, most response against encapsulated organisms is B cells coz they r non peptide entities.. So, they show inc. incidence in IgA deficiency.
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