Milk precipitins, circulating immune complexes, and IgA deficiency.

Twenty-two patients with selective IgA deficiency were studied for the presence of serum precipitins to bovine milk, bovine and fetal calf serum, and circulating immune complexes. Fifty-nine percent had circulating immune complexes, 50% had milk precipitins, 23% had precipitins to bovine serum, and 13% had precipitins to fetal calf serum. All patients with precipitating antibodies against milk or against bovine or fetal calf serum had circulating immune complexes and the precipitin titers correlated with the amount of circulating immune complexes. After one IgA-deficient patient had drunk 100 ml of milk, studies of sequential serum samples showed the presence of casein in the circulation at 60 min and the appearance of increasing amounts of immune complexes for 120 min. These findings are interpreted to indicated that in human beings the IgA system may provide a major barrier to absorption of immunogens from the gastrointestinal tract.