IgA and IgG subclass deficiency in a poor population in a developing country.

The levels of IgG, IgG subclasses, IgM and IgA were determined in serum from 17 patients with IgA deficiency and severe or frequent infections, allergy and/or autoimmunity (median age 7 years, range 2-19), 11 healthy IgA-deficient adults and 35 controls (median age 7 years, range 2-19). In serum from all groups IgG, IgM and IgA antibodies were determined against beta-lactoglobulin, E. coli O antigens and poliovirus type 1 antigen. In saliva of 15 IgA-deficient patients and 12 of the controls IgG, IgM and secretory component-carrying antibodies against E. coli O antigens and poliovirus type 1 were determined. The majority of the studied individuals lived under poor socio-economic conditions in Brazil, with consequent heavy microbial exposure. One IgA-deficient patient with rheumatoid arthritis also had IgG2 deficiency but no infectious problems. Four out of the 35 controls without any obvious infectious problems were found with IgA or IgG subclass deficiency. One of the 11 healthy IgA-deficient adults was low in the IgG2 subclass, one in IgG1 and one in IgG3. Those with symptomatic IgA deficiency had significantly higher serum IgG than the controls, especially in the age group 6-11 years. This latter group also had significantly increased serum IgG1 and IgG2 levels when compared with the age-matched controls. Salivary IgM antibodies to E. coli and poliovirus antigens were significantly higher among the symptomatic IgA-deficient individuals than among the controls. It is not clear at present whether these increased Ig levels are secondary to frequent infections and/or part of mechanisms that may compensate for the IgA deficiency.