The immunology of syphilis

Cloning structural genes for Treponema pallidum immunogens and characterisation of recombinant treponemal surface protein, P2 (P2 star)

A genomic library consisting of partially digested 10 to 20 kilobase pair fragments of Treponema pallidum deoxyribonucleic acid (DNA) was constructed using bacteriophage lambda EMBL-3 as the vector. Positive clones expressing T pallidum antigens were detected with sera from experimentally infected rabbits. Treponemal proteins ranging in molecular weight from 37,000 daltons to 120,000 daltons were identified by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and immunoblotting of phage lysate proteins. One recombinant phage was examined further and contained an insert encoding a prominent treponemal 37,000 dalton protein. The recombinant protein was not recognised by antiserum directed against a fibronectin binding treponemal adhesion that contained the same electrophoretic mobility. Neither did antibody to the recombinant 37,000 dalton protein react with any treponemal proteins purified by fibronectin affinity chromatography. The recombinant protein in Escherichia coli lysates was labelled P2 (P2 star) to differentiate it from the comigrating adhesin protein called P2. Native P2 protein was present on T pallidum surfaces as shown by radioimmunoprecipitation assays with extrinsically labelled organisms. A cross reactive molecule like P2 was not synthesised by the avirulent spirochaete, T phagedenis biotype Reiter, which indicated that P2 is a protein specific to virulent T pallidum organisms. Finally, only sera of patients with primary syphilis possessed appreciable concentrations of antibody to recombinant P2 protein.

Langerhans cells in granulomatous syphilis

In a case of granulomatous syphilis (transitional state between early and late syphilis), several Langerhans cells (LC) were present in the basal and medial part of the epidermis. Evidence of LC activation was given by the presence of many Langerhans granules, vesicles, a large Golgi apparatus and, sometimes, Golgi complexes. In some LC, signs of degeneration were visible. Langerhans granules surrounded by cytoplasmic material were present in the intercellular space of the epidermis. Apposition of lymphocytes to LC in the dermal space supports the role of LC in immunologic mechanisms. This was further confirmed by signs of phagocytosis in LC. The interaction of LC with intra-epidermal microorganisms (as, for instance, the Treponema pallidum) might be important in the development of the epidermotropic infiltration. This mainly consists of lymphocytes, which sometimes form a pseudolymphoma. A correlation between LC and granuloma formation is suggested.

Accelerated lesion development in experimental syphilis

In experimental syphilis, lesion development changes when different numbers of treponemes are injected. Lesions at sites inoculated with lower concentrations frequently exhibit delayed incubation periods, less tissue degradation, and more rapid healing. In this report I describe an unusual finding, namely, that accelerated rather than delayed incubation period occurred after intradermal inoculation of different dosages of Treponema pallidum. When rabbits were injected with only one inoculum containing 10(6), 10(5), 10(4), or 10(3) treponemes per rabbit, the corresponding incubation periods were 4.2, 7.5, 11.0 and 15.3 days, respectively. When each rabbit was injected with all four inocula on the back, the incubation periods were shortened to 3.9, 6.0, 7.0 and 8.9 days, respectively. More pronounced differences were observed with more divergent ranges of treponemal inocula. I discuss these findings in terms of the histopathology of syphilitic lesions.

Sequential changes in susceptibility to Treponema pallidum of rabbits previously infected with Treponema paraluis-cuniculi

Rabbits immunised with virulent Treponema paraluis-cuniculi were challenged intradermally with graded doses of Treponema pallidum at three, five, seven, 12, and 30 months to ascertain the level of protection to T pallidum at various intervals after immunisation.Rabbits challenged at three months after immunisation showed no protection against T pallidum and developed syphilitic lesions significantly faster than the control rabbits, which suggests that the former rabbits were immunosuppressed. Some protection was evident at five and seven months after immunisation, as fewer inoculation sites developed syphilitic lesions with challenges of 10(3), 10(2), and 10 T pallidum and lesions developed significantly slower with 10(6) challenge. Two rabbits showed significant protection at 12 months after immunisation but a third, presumably still immunosuppressed, developed lesions significantly faster than the control rabbits after challenge. At 30 months after immunisation one rabbit was completely protected and developed no lesions after challenge; the other rabbit showed only partial protection against challenge with 10(4), 10(3), and 10(2) but complete protection against challenge with 10 T pallidum.T paraluis-cuniculi appeared to induce a state of immunosuppression by three months after infection; in one rabbit this may have been 12 months. In most immunised rabbits, however, limited cross-protection to low challenge doses of T pallidum developed by five months and was also detectable at seven and 12 months. Only one rabbit was completely resistant to challenge with 10(4)T pallidum after 30 months and another was only partly immune. Thus, T paraluis-cuniculi infection does not produce a rapid pronounced cross-immunity to T pallidum in rabbits, which may thus limit its usefulness as a vaccine against syphilis.

Experimental infection of man with rabbit-virulent Treponema paraluis-cuniculi

Virulent Treponema paraluis-cuniculi was inoculated intradermally into the arm of a human volunteer and into the shaved backs of 10 rabbits. An identical, but heat-killed, preparation was inoculated into the opposite arm of the volunteer as control. A superficial and transient infection developed in the volunteer, shown by a small zone of erythema that persisted for 24 days. The control preparation caused a smaller zone of erythema that disappeared after five days. A very poor immune response was detected by standard serological tests for syphilis. The inoculated rabbits developed lesions about six days after infection and seroconverted by 84 days. The poor antitreponemal antibody response to T paraluis-cuniculi infection in the volunteer suggests that this naturally attenuated treponeme may not be suitable as a vaccine against infection with t pallidum in humans.

Influence of testicular fluid infected with Treponema pallidum on intradermal lesions

A viscous mucoid fluid occasionally accumulates after intratesticular inoculation of rabbits with Treponema pallidum. Experiments were performed to assess the effects of this testicular fluid on the development of syphilitic lesions. Intramuscular injections of this fluid altered host defences as indicated by shorter incubation periods, by reactivation of healing lesions, and by the presence of lesions at a time when solid immunity should have developed.

Rate of clearance of virulent Treponema pallidum (Nichols) from the blood stream of normal, Mycobacterium bovis BCG-treated, and immune syphilitic rabbits

The rate of clearance of virulent Treponema pallidum (Nichols) from the blood stream of normal rabbits and rabbits previously treated with Mycobacterium bovis BCG was similar, there being treponemes still circulating 8 h after intravenous inoculation. In contrast, immune syphilitic rabbits cleared the virulent treponemes within 1 to 2 hours. Rabbits with passive humoral immunity to T. pallidum (after the transfer of 70 ml of immune serum) showed a similar clearance rate to that of the immune rabbits. Rabbits previously treated with BCG and with passive humoral immunity did not show a synergistic enhanced clearance rate, it being similar to that of immune rabbits.

Limited protection of rabbits against infection with Treponema pallidum by immune rabbit sera

After intradermal infection of rabbits with 3 x 10(6) Treponema pallidum (Melbourne 1 strain) samples of serum were taken at one, two, three, four, and six months after infection. Normal rabbits were passively immunised with these sera, challenged with intradermal doses (10(4), 10(3), 10(2), 10) of T. pallidum, and the latent periods of infection, lesion diameters, and the number of inoculation sites developing into lesions were observed. The sera taken at three, four, and six months reduced the number of intradermal inoculation sites that developed into syphilitic lesions after challenge with 10 T. pallidum. These same three sera also increased the latent period of infection after challenge with 10(4) T. pallidum. The transfer of 50 ml of immune serum per rabbit over a nine-day period before challenge had very little effect on the course of the challenge infection. Only a low level of immunity in rabbits to this strain of T. pallidum appears to be mediated by immune serum but this small degree of protection did increase with time after infection. Enhanced growth of T. pallidum in the serum-recipient rabbits did not occur, thus suggesting that none of the sera was immunosuppressive.