Stimulating effect of MDP and its adjuvant-active analogues on guinea pig fibroblasts for the production of thymocyte-activating factor.

Synthetic muramyl dipeptide (MDP) could stimulate skin fibroblasts of the guinea pig to produce thymocyte-activating factor, which augments the proliferative response of thymocytes to phytohemagglutinin (PHA). Adjuvant-active analogues of MDP also stimulated fibroblasts to produce the factor, whereas adjuvant-inactive analogues failed to do so. Thus a marked parallelism was found between adjuvant activity of these compounds and the stimulating effect on fibroblasts. Thymocyte-activating factor derived from MDP-stimulated fibroblasts was found in the fraction of mol wt 30,000-60,000 by gel filtration on a Sephacryl S-200 column. Furthermore, this factor did not exhibit T cell growth factor activity.