Cell-mediated immunity during syphilis. A review

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Abstract
Evidence was presented which reinforced the complexity of the host-parasite interaction during the course of syphilis. Infection with Treponema pallidum evoked a complicated antibody response and an assortment of cell-mediated immune reactions in the host. It appeared that humoral immunity plays a minor role towards the complete elimination of syphilitic infection while the cellular limb of the immune response may be an important host defense mechanism. A state of anergy or immunosuppression may exist in the early stages of human and experimental rabbit syphilis based upon negative skin reactions to T. pallidum antigen(s), the abnormal histological appearance of lymphoid organs and impaired in vitro lymphocyte reactivity. In the later stages of the disease cellular immunity becomes activated as delayed type skin reactions can normally be elicited in tertiary syphilitics and lymphocyte behavior in cell culture appears normal. Several mechanisms were invoked to explain the delay in an effective immune response against syphilitic infection and the duration of the disease: a capsule-like substance on the outer surface of virulant T. pallidum may act as a barrier against treponemicidal antibody; this material and other biological properties of virulent treponemes could enable spirochetes to escape being engulfed by macrophages and other phagocytic cells; antigenic competition among different treponemal antigens may cause partial tolerance; T. pallidum infection may bring about the elaboration of immunosuppressive substances of host or treponemal origin which inhibit the proper function of lymphocytes, macrophages and other cell types.