Detection of nonspecific resistance to Listeria monocytogenes in rabbits infected with Treponema pallidum.

Several lines of evidence suggest that cell-mediated immunity (CMI) is suppressed in the early stages of infection caused by Treponema pallidum and becomes activated at the time that latency is induced. In the studies reported in this paper, rabbits were infected intravenously with T. pallidum and subsequently challenged with Listeria monocytogenes. Enhanced ability to suppress the growth of Listeria was detected in their livers between 3 and 5 weeks after infection with T. pallidum, corresponding to the onset and regression of the generalized syphilitic eruption. A second infection of T. pallidum 4 weeks after the first, at a time when suppression was beginning to wane, prolonged the listericidal activity. These observations support the hypothesis that infection by T. pallidum stimulates CMI, which, in turn, may play a role in inducing latency.