The Effects of Single Low Antigen Doses on Immunologic Responsiveness in Adult Rabbits

Abstract

Summary The effects of single low doses of bovine serum albumin (BSA) on immune responsiveness were studied by administering 0.1 or 1.0 mg of BSA intravenously (i.v.) to adult rabbits. Anti-BSA was detected in 50% of each group. The injection of 1.0 mg of BSA inhibited the antibody responses to challenging doses of 100 mg i.v. of BSA given 21 and 42 days later. This hyporesponsiveness was not due to the presence of circulating antigen. Following the first 100 mg BSA challenge, a transient decrease in the strength of the antibody-antigen bonds was observed. Rabbits receiving a 10-fold lower preliminary BSA dose did not exhibit immune suppression or a decrease in the strength of antibody-antigen bonds. The immunocompetent cells of these animals were affected by the 0.1-mg i.v. BSA injection, however, as demonstrated by slightly more antibody following the second 100-mg BSA challenge, a more rapid onset of immune elimination, and a higher mean effect of dilution following the second challenge. Since immunosuppression has not been observed using 10-fold lower or higher BSA doses, there appears to be something unique about a single 1.0-mg BSA injection. Although the cellular mechanisms involved remain unclear, 1.0 mg i.v. of BSA more efficiently suppressed the population of immunologically competent cells that form antibodies capable of stronger antigen binding.