Effect of carrier priming on antibody avidity in the in vivo and in vitro immune response.

The effect of carrier priming on antibody avidity was investigated under several experimental conditions. Basically, mice were carrier primed with HRBC (horse red blood cells) prior to immunization with TNP (2,4,6-trinitrophenyl) conjugated to HRBC. Immunization was performed either or in spleen cell culture, and avidity of anti-TNP antibodies was estimated from inhibition of direct PFC (plaque-forming cells) by free TNP-BSA (-bovine serum albumin). The data indicate the appropriate conditions under which carrier priming can enhance antibody avidity. The carrier effect is maximized by priming the animals with 10-10 HRBC 3-7 days before immunization with a low dose of TNP-HRBC. Hyper-immunization by repeated injections of a high dose of the conjugate does not modify the carrier effect on avidity but it delays the fall of avidity in both carrier primed and unprimed animals. These results are interpreted in terms of T- and B-cell co-operation within the framework of the maturation theory of antibody affinity. Carrier priming was also found to increase the number of direct PFC of the IgM and, mostly, of the non-IgM classes, a finding in agreement with the notion that T cells can help IgM production and the shift to IgG.