Antibody content of rabbit milk and serum following inhalation or ingestion of respiratory syncytial virus and bovine serum albumin.

The contribution of bronchus-associated or gut-associated lymphoid tissues to the development of specific immunologic reactivity in lactating mammary glands was studied by evaluating the effect of the nature of the antigen and the route of immunization on milk antibody content. Groups of pregnant rabbits were immunized with respiratory syncytial virus (RSV) and bovine serum albumin (BSA) administered i.v., per oral (p.o.) or transtracheal (i.t.) routes. The response to RSV was characterized by the regular appearance of IgA anti-RSV in the colostrum, milk, bronchial, and intestinal secretions following p.o. or i.t. immunization, but not after i.v. immunization. RSV-specific IgG appeared in the colostrum, milk, and serum regardless of the route of immunization. On the other hand, the response to BSA by all three routes of immunization was characterized by the appearance of anti-BSA in serum, colostrum and milk which was solely associated with IgG. The anti-BSA isotype did not change during the 30-day nursing period and was not affected by BSA ingestion before or during pregnancy or during nursing. If BSA was reintroduced after 20 days of nursing, a sharp rise in the Ab content of milk occurred in p.o. but not i.v. immunized dams. This increased anti-BSA was also of the IgG isotype. These observations suggest that the isotypes of specific Ab responses in the lactating mammary gland of the rabbit may be determined by the physical and chemical nature of the antigens contacted on respiratory or intestinal mucosal surfaces.