Regulatory effect of temperature and antigen upon immunity in ectothermic vertebrates. I. Influence of hapten density on the immunological and serological properties of penicilloyl-carrier conjugates.

Sodium penicillin was conjugated to sheep erythrocytes and optimal quantities, added to a 5% SRBC suspension, were determined for haemagglutination (12-5 mg/ml) and for haemolysis (50 mg/ml) using carp antibodies and carp complement. The epitope density on the BSA molecule was gradually increased, when increasing amounts of sodium-penicillin were added to a constant quantity of BSA, until a maximum of about thirty penicilloyl groups were bound. Low conjugates, having less than seven haptenic groups per one BSA molecule, were found to stimulate carp for both anti-hapten and anti-carrier antibodies. The higher conjugates having seven and more haptenic groups were found to stimulate carp for anti-panicilloyl antibodies but not for anti-BSA antibodies. A booster dose with native BSA, given to the Pen30 BSA preimmunized carp, gave rise directly to a secondary-like response. In the rabbits, however, both heavy and low conjugates were found to stimulate antibody production for the hapten as well as for the carrier. It was suggested that the modified BSA in the heavy conjugates loses its ability to stimulate B cells, probably due to a decrease in local concentration of antigenic determinants in the BSA molecule, but its ability to stimulate helper cells is not affected for this reason.