Passive transplacental immunization: influence on the detection of enteric antigen in the systemic circulation

Female New Zealand white rabbits were immunized with bovine serum albumin (BSA). Litters which had never suckled, from immunized and nonimmunized rabbits, were tested at 4 h, 24 h, and 48 h after birth. After obtaining an initial blood sample, all infant rabbits were gavaged with 100 mg of BSA plus tracer amounts of [125I]-BSA. Infant rabbits born to immunized mothers had circulating antibody before feeding and pups from nonimmunized mothers had no detectable antibody to BSA. The fed animals were sacrificed at 3-4 h after gavage. Serum obtained from cardiac and portal blood was examined for protein bound radioactivity and for the presence of immunoreactive BSA (iBSA) by electroimmunodiffusion. All infant rabbits had radioactivity in their blood. Approximately 50% of the radioactivity in the serum of infant rabbits from nonimmunized does was protein bound and all of these animals had iBSA in portal or cardiac serum samples. Of the 33 infant rabbits from immunized does, only four had protein bound radioactivity in their serum. This radioactivity appeared to be associated with circulating immune complexes of [125I]-BSA-rabbit-anti-BSA antibodies. None of the 33 infant rabbits had iBSA detectable by electroimmunodiffusion.