In vitro cell response of Treponema pallidum-infected rabbits. II. Inhibition of lymphocyte response to phytohaemagglutinin by serum of T. pallidum-infected rabbits.

Serum inhibitors of lymphocyte response to PHA were found in T. pallidum-infected rabbits. The humoral inhibitors could be detected as early as 10 days after infection and persisted for at least 6 months. The factors also suppressed the allogeneic lymphocyte response. Control, or normal, rabbit sera likewise contain serum inhibitors, but in much lower concentration. The detection of the humoral inhibitors depended on the susceptibility of the indicator lymphocytes. Cells of some rabbits were more sensitive to the inhibitors than others. In addition to serum inhibitors, lymphocytes of T. pallidum-infected animals seem to be impaired and responded to PHA less vigorously than cells of normal rabbits. The inhibitory activity is most likely the result of a complex group of substances with different physicochemical characteristics; some pre-exist and others are newly formed after infection. Problems associated with the detection of such inhibitors are discussed.