Autoimmunity in selective IgA deficiency: relationship to anti-bovine protein antibodies, circulating immune complexes and clinical disease.

To test the possibility that autoimmunity could be related to increased levels of anti-bovine antibodies and/or circulating immune complexes in selective IgA deficiency, we studied the sera of 30 consecutive patients for the quantitative level of antibody to bovine milk, the presence of antigen--antibody complexes and 10 selected autoantibodies. Higher titres of anti-milk antibody and circulating immune complexes were to be correlated with positive serological tests of autoimmunity in these patients, and rheumatoid arthritis (three cases) and neurological disease (four cases) were found in individuals who had both milk precipitins and circulating immune complexes. We suggest that the chronic excessive permeability of the gastrointestinal tract in selective IgA deficiency may permit the excessive absorption of many food proteins, leading to the formation of antigen--antibody complexes and autoimmunity.