It is the most common congenital immunodeficiency syndrome. When IgA-bearing B lymphocytes fail to mature into IgA-secreting plasma cells, serum IgA levels are reduced ensuing IgA deficiency.
Failure of terminal B-cell differentiation is attributed to:
(1) an intrinsic B-cell defect,
(2) inadequate or defective T-helper cells,
(3) presence of or excessive IgA- specific T-cell suppressor cells, and
(4) passage of maternal anti-IgA antibodies that suppress fetal IgA development.
IgA antibody deficiency disease may be asymptomatic, but more commonly it leads to recurrent respiratory and digestive tract infections.
Since IgA antibodies present in mucosal layer gives protection to respiratory and digestive tracts, in the absence of IgA intact pathogens are able to penetrate mucosal surfaces and cause infections. Individuals with IgA deficiency tend to develop type II hypersensitivity (immune complex disease) problems.
Unlike more generalized ‘hypo-gamma-globulinemias’. IgA deficiency could not be treated with gama globulin therapy.
Since the person with IgA deficiency is capable of producing normal amounts of other antibodies, their immune system may recognize injected IgA as foreign body and produce antibodies against the injected antibodies resulting in the formation of immune complex triggering ‘immune complex syndrome’.
IgA antibody deficiency is associated with deficiencies of certain IgG subclasses. Because in intrinsic B-cell defect, the alpha one gene may be deleted along with other heavy-chain genes, homozygous deletions of large portions of the Ig heavy-chain locus may result in complete absence of 3 or more Ig classes (IgG2, IgG4, IgAl, and occasionally IgE). IgG2 subclass deficiency is most commonly associated with IgA deficiency.