Autoimmunity in selective IgA deficiency.

Several antibodies have been reported in selective IgA deficiency and we have detected antibodies to human IgM and native human collagen in 35 and 34%, respectively, of 60 such subjects (compared to 1.6 and 2.0%, respectively, in normal controls). The anti-IgM isoantibodies are clearly distinguishable from antibodies to ruminant proteins and there was no statistically significant association between different antibodies and clinical features in individual patients. The etiology of the antibodies remains unknown.