Nonspecific activation of murine spleen cells in vitro by a synthetic immunoadjuvant ( N-acetyl-muramyl- l-alanyl- d-isoglutamine)

We reported previously that synthetic N-acetyl-muramyl- l-alanyl- d-isoglutamine (MDP) displayed marked adjuvant activity but was devoid of mitogenicity in vitro. The data reported here establish that, under different cultural conditions, thymidine uptake and blast cells can be increased by MDP in spleen cells of DBA/2 and Balb/c mouse strains. Optimal responses were obtained on culture in a serum-free medium supplemented with 2-mercaptoethanol for 4 or 5 days. This effect was also obtained with spleen cells of Balb/c nude mice. When the synthetic MDP was compared to a natural water-soluble adjuvant (neo-WSA), extracted from Mycobacterium smegmatis cells, both were found to stimulate [ 3H] thymidine incorporation by mouse spleen cells. However, with the neo-WSA, the effect peaked on Day 2 and was weak or absent on Days 4 and 5. When the cells were cultured in a medium containing fetal calf serum, neo-WSA activation was completely abolished, while MDP-mediated stimulation was decreased.