THE DEVELOPMENT OF HUMORAL IMMUNOLOGICAL MEMORY TO A T-CELL-DEPENDENTANTIGEN REQUIRES THYMIC EMIGRANT CELLS

Immunological memory is embodied in the rapid and enhanced immune resp onsiveness to previously encountered antigens. Classically, memory wou ld depend on the presence of small resting long-lived specific lymphoc ytes which, through clonal expansion after priming with antigen, would be present at higher frequencies than in naive animals. Here we repor t that T-cell-reconstituted athymic mice, which lack recent thymic emi grants, mount a primary response to a T-cell-dependent antigen, but do not develop memory or the capacity to produce specific anti-TNP IgG1 antibodies during the secondary immune response. On the other hand, if thymocytes are continuously provided during the secondary response, a typical secondary immune response is achieved with high levels of spe cific IgG1. These results lead us to propose that the development of h umoral immunological memory cannot be explained solely by the long lif e span of primed T lymphocytes, but is rather a dynamic state dependen t on the continuous presence of recent thymic emigrants and qualitativ e functional differences in responder T cells.