In vitro effect of MS D 53 and its fractions on human mononuclear cells

The present study was designed to investigate the in vitro effect of the bacterial derivative MS D 53 and its components (ribosomal fraction and membrane proteoglycans) on different functions of human peripheral blood mononuclear cells (PBM). MS D 53 induced IL-1β production by unstimulated monocytes. This effect was particularly evident for the highest concentration of the drug (100 μg/ml), which showed an IL-1β inducing activity comparable to phorbol-12-myristate-13-acetate stimulus. Ribosomal fraction (RF) and membrane proteoglycan (MP) were less efficient than MS D 53 in stimulating IL-1β secretion, indicating an additive effect in the whole drug. MS D 53 and, to a lesser extent, RF enhanced spontaneous 3H-TdR uptake in normal adult PBM but not in cord-blood mononuclear cells, suggesting a possible anamnestic response towards common bacterial antigens. MS D 53 (100 μg/ml) also increased blastogenesis induced by mitogenic concentrations of PHA or anti-CD3 monoclonal antibody. In the costimulation assay performed with sub-mitogenic concentrations of anti-CD3 plus exogenous rIL-2, the whole drug and, to a lesser extent, the two fractions, induced a dose-dependent increase of proliferative response. This effect could be due both to the specific antigenic response and to actual immunomodulatory activity.