Enhancement by muramyl dipeptide of in vitro nude mice responses to a T-dependent antigen.

N-acetyl-muramyl-L-alanyl-D-isoglutamine (referred to as MDP for muramyl dipeptide) has been shown to enhance in vivo and in vitro immune responses to various antigens. It has previously been reported that in the case of T-dependent antigens, the adjuvant activity of MDP was mediated by a helper T-cell. Our present findings demonstrate that in vitro responses of nude mice spleen cells to T-independent, TNP-PAA or T-dependent SRBC can also be markedly increased by this synthetic adjuvant. Moreover, under the same conditions, MDP produced polyclonal activation.