Bovine antigens and the formation of circulating immune complexes in selective immunoglobulin A deficiency.

We have shown that levels of circulating immune complexes are closely associated with the presence of precipitating antibodies to bovine milk proteins in individuals with selective immunoglobin (Ig)A deficiency. To test whether milk proteins are involved in immune complex formation, sera of seven IgA-deficient individuals were studied for the appearance of complexes after milk ingestion. In three of the seven, an initial fall in the level of complexes was followed by an increasing value, which peaked at 120-150 min. In another three, there was a tendency toward the formation of two peaks of complexes, the first at 30-60 min and the second at 120-150 min after drinking milk. One subject, who had had recent treatment for two separate neoplasms, had a steady level of complexes that did not change during the course of this test. After drinking milk, the molecular weight of the complexes found in the sera of one individual at the start of the milk test fell from >19S to 7-11S, and in vitro additions of progressively increasing amounts of a mixture of milk proteins or bovine gamma globulin, to sera that contained complexes produced a progressive reduction in the level of complexes detectable. We conclude that the circulating immune complexes found in some patients who lack IgA contain bovine milk proteins and that periodic fluctuation of the molecular weight of such complexes, depending upon antigen ingestion, appears likely. It remains uncertain what effect the chronic circulation of complexes has upon the clinical state of this group of patients.