Suppression of human lymphocyte responses by oral spirochetes: a monocyte-dependent phenomenon.

Spirochetes have been implicated in the pathogenesis of several human infections including syphilis, yaws, Lyme disease, and periodontal diseases. We examined soluble sonic extracts of oral spirochetes (Treponema denticola and T. vincentii) for their ability to alter human lymphocyte function. These organisms were isolated from subgingival plaque of patients with periodontitis. We found that sonicates of several but not all strains of T. denticola caused a dose-dependent inhibition of human lymphocyte responsiveness to Con A, PHA, PWM, and the recall antigen SKSD. Suppression involved alterations in DNA, RNA, and protein synthesis; there was no effect on cell viability. In contrast, sonicates of T. vincentii (medium-sized spirochetes) had no demonstrable effects on lymphocyte activation. The suppressive factor derived from T. denticola is heat-labile with a m.w. of approximately 100,000. To achieve maximal suppression, sonicates had to be added during the first 24 hr of incubation; there was no inhibition observed when added at 48 or 72 hr (along with 3H-TdR). Suppression was dependent on the presence of adherent monocytes; removal of these cells prevented spirochete-induced suppression of lymphocyte proliferation. Furthermore, the combination of indomethacin and catalase were able to reverse (or prevent) the inhibitory effects of the spirochete extracts, demonstrating a requirement for both prostaglandins and hydrogen peroxide. The potential role of such suppressive factors in periodontal disease is discussed.