Milk protein immune complexes in the cow and calf.

Immune complexes formed between IgG and the milk protein beta-lactoglobulin have detected in bovine colostrum and in the serum of young calves. Complexes were present in all calves studied and the data suggest that they were passively acquired during suckling. The complexes had a molecular weight of 185 000 strongly suggesting the molecular configuration Ab1Ag2. Their half-life in calf serum was 12-21 days. alpha-Lactalbumin was also detected in calf serum and appeared to be complexed in a similar way. Attempts to dissociate the complexes at low pH and by reduction and separation of IgG heavy and light chains led to the release of only a small percentage of complexed beta-lactoglobulin. The results suggest that transient autoimmunity to milk and the transfer of milk protein complexes from mother to young are normal events in cattle. An immunosuppressive role for the immune complexes in postulated.