Development of immunological memory in rainbow trout (Oncorhynchus mykiss). I. An immunochemical and cellular analysis of the B cell response.

In vivo and in vitro analyses of the antibody responses of rainbow trout (Oncorhynchus mykiss) confirmed the existence of immunological memory in this species. An enhanced in vitro secondary antibody response was found to be due strictly to an expansion of the antigen-sensitive precursor pool without a concomitant increase in clone size. In contrast to the development of immunological memory in mammalian species, there was no evidence for affinity maturation during the primary or secondary response. A distinct shift in the fine specificity profiles of the antibodies, however, did occur during the generation of the secondary response. Additionally, more than a single injection of the priming antigen, TNP-KLH was required to produce an enhanced in vitro response to this T-dependent antigen. However, a second priming injection was not required to produce an enhanced secondary response to the T-independent form of antigen, TNP-LPS. These results indicate that memory in trout may be due to a simple expansion of the antigen-specific precursor pool without many of the qualitative changes in antibody or B cell function associated with the expression of memory in mammals.