Inhibitory effects of extracellular products from oral bacteria on human fibroblasts and stimulated lymphocytes

Extracellular products of 12 strains of Streptococcus mutans and 5 additional species of oral bacteria were analyzed for their ability to inhibit proliferation of fibroblastoid cells (HeLa and AV3) and blast transformation of human peripheral blood lymphocytes obtained from normal individuals. Products from S. mutans strains AHT and BHT, Streptococcus intermedius, and Actinomyces viscosus inhibited [3H]thymidine uptake by fibroblastoid cells and phytohemagglutinin-stimulated lymphocytes. Products from S. mutans E49, Streptococcus salivarius, and Actinomyces naeslundii inhibited blast transformation of human lymphocytes but did not significantly inhibit the growth of fibroblastoid cells. Preparations from S. intermedius gave the greatest inhibitory activity against both target cell types; initial characterization of this preparation suggested a single factor active in both assays, in that the heat lability and Sephadex G-200 elution profile were similar for the inhibitory activity seen with the two cell types. The molecular weight of the inhibitor, estimated by gel filtration on Sephadex G-200 and Ultragel AcA34, was approximately 160,000. The results strongly suggest that oral bacteria produce heat-labile substances that interfere with fibroblast proliferation and alter the lymphocytic immunological response.