Carrier-specific immune memory to a thymus-independent antigen in congenitally athymic mice

Immune memory to the DNP epitope coupled to a nonmitogenic thymus-independent carrier, Ficoll, was demonstrated in congenitally athymic outbred Swiss mice. Strong IgM and modest IgG components of this memory were detected. Moreover, this memory was carrier specific since it was elicitable only when DNP-Ficoll primed mice were challenged with DNP-Ficoll and not when similarly primed mice were challenged with DNP coupled to pneumococcal polysaccharide or to keyhole limpet hemocyanin. Ficoll primed mice also demonstrated a memory response when challenged with DNP-Ficoll. These findings indicate that a non-T cell, presumably a B cell, is capable of recognizing the carrier epitopes of this thymus-independent hapten-carrier complex. Unlike their athymic counterparts, euthymic mice of the same genetic background failed to demonstrate the IgM component of this memory, but they did demonstrate modest carrier-specific IgG memory. These results strongly suggest that suppressor T cells are either directly or indirectly important in regulating the IgM memory response of these mice to DNP-Ficoll. Indirect regulation could possibly occur via an antibody-mediated specific immune suppression mechanism.