Suppressive effect of soluble factor(s) derived from Prevotella loescheii ATCC 15930 on proliferation of human lymphocytes.

Soluble sonic extracts of Prevotella loescheii caused a dose-dependent inhibition of human peripheral blood lymphocyte proliferation by mitogen and of the proliferation of a leukemic cell line, BALL-1, when assessed by DNA synthesis (3H-thymidine incorporation). RNA (3H-uridine incorporation) and protein (3H-leucine incorporation) synthesis were similarly altered after exposure to the extract. There was no effect on cell viability as measured by either trypan blue exclusion or extracellular release of the cytoplasmic enzyme lactate dehydrogenase. Preliminary characterization indicates the suppressive factor(s) derived from P. loescheii to be a protein since it is heat-labile and trypsin-sensitive. The factor eluted in a peak on a high-pressure liquid chromatography gel filtration corresponding to a molecular weight of approximately 32,000. Since black-pigmented anaerobic rods have been implicated in the pathogenesis of periodontal disease, the data suggest that P. loescheii contributes to the disease process by suppressing lymphocyte function.