Specific IgM and IgG antibodies in IgA deficiency.

Evidence of an abnormality of IgM- and IgG-specific antibody responses was sought in subjects with selective IgA deficiency. Twenty-four patients having a serum IgA level less than 0 . 37 g/l were detected by local-population screening. Total IgM and IgG levels were measured as well as specific antibody to the lipopolysaccharides of six 0 serotypes of E. coli which are frequently isolated from human faeces. Serum IgM-class E. coli antibodies were significantly lower in IgA-deficient patients than in age- and sex-matched controls. The respective IgG-class antibody was generally elevated although more variation existed in this class. There was no correlation of specific antibody in either class with the degree of IgA deficiency. Possible explanations for these patterns of antibody response are discussed. It is concluded that some subjects with 'selective IgA deficiency' may be deficient in specific IgM antibody responses to certain antigens.