Development of of macrophage migration inhibition in rabbits infected with virulent Treponema pallidum

Contribution of rabbit leukocyte defensins to the host response in experimental syphilis

In the companion paper (L. A. Borenstein, M. E. Selsted, R. I. Lehrer, and J. N. Miller, Infect. Immun. 59:1359-1367, 1991), we report that rabbit alveolar macrophage and neutrophil derived defensins possess antimicrobial activity against Treponema pallidum subsp. pallidum, the etiologic agent of syphilis. In this study, antisera specific for NP-1 and NP-2 (defensins present in certain macrophages and polymorphonuclear leukocytes) and NP-5 (a defensin produced only in neutrophils) were used to detect these peptides by immunoperoxidase staining in testicular lesions from infected rabbits. Profound amounts of cell-free and cell-associated defensins were detected in the tunica albuginea and interstitial spaces during the first 24 h of infection. The presence of defensins was transient and almost undetectable by day 4. Interstitial defensins were detected again at day 10 and increased through day 16, at which time lesion healing was evident by hematoxylin and eosin staining. The appearance and increase in detectable defensins between days 10 and 16 of infection correlated with a reduction in numbers and disappearance of T. pallidum, as demonstrated by using silver staining. The extent and pattern of immunostaining for NP-1 and NP-2 corresponded with immunostaining for NP-5 and identified neutrophils as the cellular source of the defensins. These findings indicate that defensins may contribute to the control of local T. pallidum infection and suggest a role for acute inflammatory processes in the resolution of early experimental syphilis.

Treponema pallidum receptor binding proteins interact with fibronectin

Analysis of plasma proteins avidly bound to T. pallidum surfaces revealed the ability of T. pallidum to acquire numerous host macromolecules. No acquisition was evident by the avirulent spirochete, T. phagedenis biotype Reiter. Western blotting technology using hyperimmune antifibronectin serum as a probe revealed the ability of virulent treponemes to avidly bind fibronectin from a complex medium such as plasma. The specificity of the tiplike adherence of motile T. pallidum to fibronectin-coated glass surfaces and to fibronectin on HEp-2 cells was reinforced by the observation that pretreatment of coverslips or cell monolayers with monospecific antiserum against fibronectin substantially reduced T. pallidum attachment. The stoichiometric binding of T. pallidum to fibronectin-coated coverslips and the inability of unlabeled or 35S-radiolabeled treponemes to interact with glass surfaces treated with other plasma proteins further established the specific nature of the interaction between virulent T. pallidum and fibronectin. The avid association between three outer envelope proteins of T. pallidum and fibronectin was also demonstrated. These treponemal surface proteins have been previously identified as putative receptor-binding proteins responsible for T. pallidum parasitism of host cells. The data suggest that surface fibronectin mediates tip-oriented attachment of T. pallidum to host cells via a receptor-ligand mechanism of recognition.

Activation of macrophages by products of lymphocytes from normal and syphilitic rabbits

The production of soluble macrophage-activating factors by lymphocytes from syphilitic and normal rabbits was examined. Culture supernatants of splenic lymphocytes cultured with Treponema pallidum antigens or concanavalin A were incubated with rabbit peritoneal macrophages in vitro. The macrophage monolayers were then washed and infected with log-phase Listeria monocytogenes. Activation of the macrophages by lymphocyte products was measured by the ability of the macrophages to resist intracellular multiplication of Listeria and thus survive infection. Macrophages incubated with supernatants of unstimulated lymphocytes or T. pallidum-stimulated lymphocytes from normal rabbits were unable to resist intracellular multiplication of Listeria. Specifically stimulated lymphocytes from syphilitic rabbits and mitogen-stimulated lymphocytes from both normal and syphilitic rabbits demonstrated a clear ability to produce soluble factors which conferred upon macrophages the ability to limit the intracellular growth of the bacteria. Antigen or mitogen alone was unable to activate the macrophages; the presence of lymphocyte products was required.

A histopathologic and immunologic study of the course of syphilis in the experimentally infected rabbit. Demonstration of long-lasting cellular immunity

Inoculation of the causative agent of syphilis, Treponema pallidum into the testes of rabbits initiated the following sequence of events: 1) a rapid proliferation of organisms in the interstitial tissues of the testes, reaching a maximum at about 10-11 days after infection; 2) systemic spread of organisms primarily in the lymphoid organs; 3) a prompt immune response manifested by hyperplasia of T cell domains in draining lymph nodes and spleen, blast transformation responses of lymphoid cells to sonicates of T pallidum, the appearance of serum antibody, and the marked infiltration of the infected areas of the testes by T cells; 4) essential clearing of organisms identified by immunofluorescence from the infected site 10-14 days after infection associated with evolution of the inflammatory response from primarily a T cell infiltrate to a larger mononuclear cell type, and the immunofluorescent identification of presumptive T pallidum antigen in macrophages; 5) interstitial fibrosis or resolution 17-21 days after infection so that examination of infected testes from 1 to 24 months later reveals foci of tubular atrophy and fibrosis of varying size, alternating with regenerated tubules, separated by interstitial areas with only minimal fibrosis. During the long period of latency there is no evidence of atrophy or hypoplasia of the lymphoid organs and long-lasting T cell memory with regard to T pallidum sonicates is demonstrable. Reinfection of previously inoculated rabbits indicates partial protection at 25 days after infection followed by essentially complete protection after 55 days. It is concluded that there is a prompt and long-lasting immune response to T pallidum in experimentally infected rabbits. The main mechanism for destruction of infecting organisms appears to be T-cell-initiated macrophage-mediated destruction, but a role for antibody dependent phagocytosis cannot be ruled out. The reason that some organisms may survive in various body organs remains unknown, but possible explanations are presented.

T lymphoid cells in primary syphilis. Quantitative studies

In previous studies to assess the role of cell-mediated immunity in Treponema pallidum infection investigations of delayed type skin hypersensitivity tests, lymphocyte transformation test, leucocyte migration inhibition tests, and histological studies of the reticuloendothelial system have been performed. In this study, the numbers of T (thymus-dependent ) lymphoid cells in 10 patients with primary syphilis (eight untreated) were estimated by the rosette technique. Results indicate a significant decrease in the number of T lymphoid cells in patients with primary syphilis.

Aberrant secondary antibody responses to sheep erythrocytes in rabbits with experimental syphilis

Rabbits infected with Treponema pallidum have strikingly depressed in vivo immunoglobulin G responses to sheep erythrocytes. To gain further insight into the nature of this suppression, the immune responses of splenic and peripheral blood lymphocytes from infected rabbits to sheep erythrocytes were studied in vitro. Spleen cells from rabbits that had been sensitized with sheep erythrocytes during active syphilis had greatly decreased immunoglobulin M and G responses after in vitro incubation with sheep erythrocytes, when compared to the results obtained with cells from sensitized uninfected animals. Suppressor cells could be demonstrated in peripheral blood lymphocytes of control rabbits 6 months after sensitization with sheep erythrocytes; these cells could be removed by nylon wool filtration. When primary sensitization with sheep erythrocytes was carried out during active syphilis, these suppressor cells were not detectable in peripheral blood lymphocytes 6 to 9 months later. These findings provide further evidence that induction of immune responses may be abnormal early in treponemal infection and may help to explain the failure of the host to produce antibodies which eradicate the organism during the first 2 to 3 months of infection.

Cell-mediated immunity during syphilis

Evidence is presented which reinforces the complexity of the host-parasite interaction during the course of syphilis. Infection with Treponema pallidum evokes a complicated antibody response and an assortment of cell-mediated immune reactions in the host. It appears 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 defence mechanism. Information now available indicates that a state of anergy, or immunosuppression, exists 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. It is also evident that 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 behaviour in cell culture appears normal. Several mechanisms have been invoked to explain the delay in an effective immune response against syphilitic infection and the duration of the disease: (1) a capsule-like substance on the outer surface of virulant T. pallidum may act as a barrier against treponemicidal antibody; (2) this material and other biological properties of virulent treponemes could enable spirochaetes to escape being engulfed by macrophages and other phagocytic cells; (3) antigenic competition among different treponemal antigens causing partial tolerance; (4) 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.