Non-specific T-cell replacing factor fails to promote a secondary response in vivo.

The supernatant from concanavalin-A-treated cultures has been used in vivo in nude mice to investigate the nature of the antibody response that can be induced after injection of this non-specific T-cell replacing factor (NSF). Although NSF alone does not induce a response, it permits a greatly augmented response to sheep erythrocytes. This response is, however, restricted to IgM and is not accompanied by development of memory. No secondary response could be obtained with antigen alone or with NSF and antigen, and there was usually no response even if normal congenic thymus cells were injected with antigen into animals that had responded to NSF and antigen.