Effect of immune serum and its immunoglobulin fractions on hamsters challenged with Treponema pallidum ssp. pertenue

Endemic treponemal diseases

The endemic treponemal diseases, consisting of yaws, bejel (endemic syphilis) and pinta, are non-venereal infections closely related to syphilis, and are recognized by WHO as neglected tropical diseases (NTDs). Despite previous worldwide eradication efforts the prevalence of yaws has rebounded in recent years and the disease is now a major public health problem in 14 countries. Adequate data on the epidemiology of bejel and pinta is lacking. Each disease is restricted to a specific ecological niche but all predominantly affect poor, rural communities. As with venereal syphilis, the clinical manifestations of the endemic treponemal diseases are variable and can be broken down in to early stage and late stage disease. Current diagnostic techniques are unable to distinguish the different causative species but newer molecular techniques are now making this possible. Penicillin has long been considered the mainstay of treatment for the endemic treponemal diseases but the recent discovery that azithromycin is effective in the treatment of yaws has renewed interest in these most neglected of the NTDs, and raised hopes that global eradication may finally be possible.

A monoclonal antibody that conveys in vitro killing and partial protection in experimental syphilis binds a phosphorylcholine surface epitope of Treponema pallidum

Immunization with purified Treponema pallidum outer membrane vesicles (OMV) has previously resulted in high-titer complement-dependent serum bactericidal activity. In this study, OMV immunization resulted in the isolation of a monoclonal antibody, M131, with complement-dependent killing activity. Passive immunization of rabbits with M131 administered intravenously conferred significant immunity demonstrated by the failure of syphilitic lesions to appear at 29% of intradermal challenge sites (7/24) and a mean delay of approximately 8 days to lesion appearance at the remaining sites (17/24). M131 not only bound to OMV and to the surfaces of intact motile T. pallidum cells but also bound to organisms whose outer membranes were removed, indicating both surface and subsurface locations for the killing target. This target was determined to be a T. pallidum lipid. Lipid extracted from T. pallidum and made into liposomes bound M131. Reverse-phase high-pressure liquid chromatography separation and fraction collection mass spectrometry (LC-MS+) of T. pallidum lipid showed that the target of M131 was phosphorylcholine. M131 binding required both liposome formation and a critical concentration of phospholipid containing phosphorylcholine, suggesting that the epitope has both a conformational and a compositional requirement. M131 did not react with red blood cells, which have phosphorylcholine-containing lipids in their exterior membrane leaflets, or with Venereal Disease Research Laboratory antigen that also contains phosphorylcholine, further indicating the specificity of M131. This is the first physical demonstration of an antigen on the T. pallidum surface and indication that such a surface antigen can be a target of immunity.

Treponema pallidum subsp. pertenue displays pathogenic properties different from those of T. pallidum subsp. pallidum

The present study described the susceptibility of C4D guinea pigs to cutaneous infection with Treponema pallidum subsp. pertenue Haiti B strain. The general manifestations of the disease in adults and neonates differ, to a certain degree, from those induced by T. pallidum subsp. pallidum Nichols strain. Noticeable differences between the infections were reflected in the character of the skin lesions, their onset and persistence, and the kinetics of the humoral response. The incidence and dissemination of cutaneous yaws lesions in very young guinea pigs were remarkably different from the low frequency observed in a similar age group of syphilis infection, 100 versus 17%, respectively. Moreover, as opposed to T. pallidum subsp. pallidum, T. pallidum subsp. pertenue does not cross the placenta. Offspring born to yaws-infected mothers did not produce immunoglobulin M antibodies and their organs, examined by PCR and rabbit infectivity test (RIT), were all negative. Examination of a large number of tissues and organs in adult, neonate, and maternal yaws by PCR and RIT clearly demonstrated that, unlike syphilis, there was a low incidence and short persistence of the yaws pathogen in internal organs. These findings stress the dermotropic rather than the organotropic character of yaws and provide further evidence of distinctive biological and pathological differences between yaws and venereal syphilis.

Effect of passive immunization with purified specific or cross-reacting immunoglobulin G antibodies against Treponema pallidum on the course of infection in guinea pigs

Whole immune serum or highly purified immunoglobulin G (IgG) antibodies to Treponema pallidum exhaustively adsorbed with three strains of nonpathogenic treponemes (TPI-IgG) were used for passive immunization of inbred strain 2 guinea pigs before and after intradermal challenge with 3.4 x 10(7) virulent T. pallidum Nichols organisms. Before challenge, control animals received a similarly purified IgG fraction containing either a cocktail of antibodies against three nonpathogenic treponemes (NPTI-IgG) or IgG prepared from normal guinea pig serum (NGPS-IgG). The purified fractions contained both IgG1 and IgG2 isotypes. The antibody levels (detected by fluorescent treponemal antibody test and enzyme-linked immunosorbent assay) and molecular specificities (immunoblot) of sera obtained from recipient animals before infection reflected those of the purified fractions used for immunization. Three protocols of passive immunization were used. Whole immune serum containing specific and cross-reacting antibodies afforded better protection than TPI-IgG even though asymptomatic animals were not fully protected. A single intradermal injection (0.1 ml) of TPI-IgG or NPTI-IgG into one hind leg 22 h before infection at the same site provided relatively higher protection than multiple intravenous injections (total, 15 ml) of the respective individual preparations. Since purified NGPS-IgG injected in the same animals, into the opposite hind leg, failed to protect against the challenging infection, it is reasonable to assume that specific and cross-reacting antitreponemal antibodies of the IgG1 subclass, which in guinea pigs are homocytotropic, play a relevant role in local protection.

Role of L3T4+ and 38+ T-cell subsets in resistance against infection with Treponema pallidum subsp. pertenue in hamsters

The protective immunity conferred by T-cell subsets against infection with Treponema pallidum subsp. pertenue was studied. We demonstrated that hamster T cells can be separated into two subsets by monoclonal antibody (MAb) GK 1.5 (anti-L3T4) and MAb 38. Eighty-five percent of hamster thymocytes were L3T4+ and 87% were 38+ cells; 84% were dual positive for MAbs anti-L3T4 and 38. In the peripheral lymph nodes, however, the L3T4+ and 38+ T cells were mutually exclusive according to two-color immunofluorescence analysis. The two T-cell subsets were found to be functionally distinct according to their secretion of interleukin 2 (IL-2) when stimulated with concanavalin A. The L3T4+ cells secreted IL-2 and had characteristics of T helper cells, while the 38+ cells did not secrete IL-2 and appeared to be T cytotoxic-suppressor cells. Transfer of 4 x 10(6) helper or cytotoxic-suppressor T lymphocytes from T. pallidum subsp. pertenue-immune hamsters protected irradiated naive hamsters against challenge with this subspecies. IL-2 production could still be detected in the irradiated recipients 12 days after irradiation of naive recipients, although at a low level. This suggests that the remaining lymph node cells could support the survival and expansion of the infused cytotoxic-suppressor T cells. No accumulation of macrophages was observed in regional lymph nodes of immune T-cell recipients within 10 days of infection. Instead, there was an influx of polymorphonuclear neutrophils in all animals injected with T. pallidum subsp. pertenue. This report demonstrates that hamster T cells can be separated into two phenotypically and functionally distinct subsets and that both T-cell subsets confer protection against challenge with T. pallidum subsp. pertenue.

Immune T cells sorted by flow cytometry confer protection against infection with Treponema pallidum subsp. pertenue in hamsters

The role of cell-mediated immunity against infection with Treponema pallidum subsp. pertenue in humans or experimental animals is unclear. Hamsters injected subcutaneously in the hind paws with 4 x 10(6) unfractionated lymph node cells or enriched lymph node T cells (immunoglobulin negative, Ia negative) from T. pallidum subsp. pertenue-immune hamsters were resistant to challenge with T. pallidum subsp. pertenue. The popliteal lymph nodes of hamsters that received immune cells weighed less and had significantly fewer treponemes than did lymph nodes from hamsters infused with cells from nonimmune donors. Furthermore, recipients of immune T cells failed to develop antitreponemal antibodies 21 days after challenge. Enriched T cells were obtained by flow cytometric separation by using monoclonal anti-Ia antibody 14-4-4s, which identified hamster B cells. Flow cytometric analysis by two-color immunofluorescent staining with anti-hamster-immunoglobulin and monoclonal anti-Ia antibody 14-4-4s confirmed that monoclonal anti-Ia antibody 14-4-4s recognized B cells. In addition, lymph node cells obtained after treatment with anti-Ia monoclonal antibody 14-4-4s and complement were 97% T cells, as determined by monoclonal antibody 20, a hamster T-cell marker. These results demonstrated that highly enriched T cells (immunoglobulin negative, Ia negative) from T. pallidum subsp. pertenue-immune hamsters conferred partial protection on hamsters against infection with T. pallidum subsp. pertenue.

Phagocytosis of opsonized Treponema pallidum subsp. pallidum proceeds slowly

Macrophages were found to phagocytize Treponema pallidum subsp. pallidum attached to polycarbonate filters. This environment simulated the in vivo interaction of surface-adherent treponemes with macrophages. The phagocytosis of T. pallidum subsp. pallidum was found to proceed slowly. Heat-killed T. pallidum subsp. pallidum were susceptible to opsonization with 2% immune serum, whereas live treponemes were resistant to this concentration of antibody. High concentrations of immune serum were found to increase phagocytosis of the spirochetes. Live T. pallidum subsp. pallidum had bound limited quantities of immunoglobulin G in vivo, and only opsonization with 20% immune serum resulted in a detectable increase in surface-bound immunoglobulin in vitro. Kinetic studies suggested a steady rate of phagocytosis that is considerably slower than with other bacteria. Scanning electron microscopy studies of the phagocytizing macrophages showed that the treponemes were detached from the membrane filters and scooped onto the ruffled portion of the macrophage surface. This lengthy physical process, along with the lack of a dramatic increase in ingestion after opsonization, may account for the slow rate of phagocytosis.