PCR testing for Treponema pallidum in paraffin-embedded skin biopsy specimens: test design and impact on the diagnosis of syphilis

BACKGROUND

Syphilis, a chronic infection caused by Treponema pallidum, is a disease which is increasing in incidence, and thus more and more becoming a differential diagnosis in routine pathology.

AIMS

To develop a PCR-based molecular assay for the detection of T pallidum in formalin-fixed, paraffin-embedded tissues, and evaluate its diagnostic power, especially in comparison with other ancillary methods (immunohistochemistry and Dieterle staining).

METHODS

36 skin biopsy specimens with the clinical and/or serological diagnosis of syphilis were evaluated by morphology, immunohistochemistry and silver staining. A semi-nested PCR assay targeting the T pallidum DNA polymerase A gene was designed and applied. Specificity of amplification was confirmed by direct sequencing of PCR products.

RESULTS

Overall, the presence of T pallidum was detected in skin biopsy specimens in 20 cases, by immunohistochemistry, Dieterle staining, or PCR. Immunohistochemistry testing was positive in 17/35 cases tested, and Dieterle staining in 9/35 cases tested. In comparison, PCR testing was positive in 14/36 cases, and highly dependent on the tissue quality. When excluding cases with compromised DNA quality, PCR testing was positive in all cases except one, including three cases negative by immunohistochemistry and Dieterle staining.

CONCLUSIONS

PCR testing is significantly more sensitive than silver staining, and provided that DNA quality is sufficient, at least as sensitive as immunohistochemistry for the detection of T pallidum in formalin-fixed, paraffin-embedded skin biopsy specimens. Therefore, it is a useful ancillary tool in the histological diagnosis of syphilis.

Quantitation of rabbit cytokine mRNA by real-time RT-PCR

Fundamental understanding of rabbit immunology and the use of the rabbit as a disease model have long been hindered by the lack of immunological assays specific to this species. In the present study, we sought to develop a method to quantitate cytokine expression in rabbit cells and tissues. We report the development of a quantitative real-time RT-PCR method for measuring the relative levels of rabbit IFN-gamma, IL-2, IL-4, IL-10 and TNF-alpha mRNA. Quantitation was accomplished by comparison to a standard curve generated using plasmid DNA containing partial sequences of the relevant cytokines. Experimental studies demonstrate applicability of this assay to quantitate cytokine mRNA levels from rabbit spleen cells following mitogen stimulation. We have further utilized this assay to also examine cytokine expression in rabbit tissues during experimental syphilis infection.

Subfamily I Treponema pallidum repeat protein family: sequence variation and immunity

A 12-membered Treponema pallidum repeat (Tpr) protein family has been identified in T. pallidum subsp. pallidum, the causative agent of syphilis. The subfamily I Tpr proteins (C, D, F, and I) possess conserved sequence at the N- and C-termini and central regions that differentiate the members. These proteins may be important in the immune response during syphilis infection and in protective immunity. Strong antibody responses have been observed toward some of the subfamily I Tpr proteins during infection with different syphilis isolates. Some sequence variation has also been identified in one subfamily I Tpr member, TprD, among T. pallidum subsp. pallidum isolates. In this study, we examined sequences in the remaining subfamily I Tpr proteins among strains. Both TprF and TprI were conserved among T. pallidum subsp. pallidum isolates. While some heterogeneity was identified in TprC. We further examined the immune response and protective capacity of TprF protein in this paper. We demonstrate that the N-terminal conserved region of the subfamily I Tpr proteins elicits strong antibody and T-cell responses during infection, and immunization with this region attenuates syphilitic lesion development upon infectious challenge.

Activated and mature CD83-positive dendritic cells and interferon-gamma-positive cells in skin eruptions of secondary syphilis

Dendritic cells are considered to be the most potent antigen-presenting cells, and CD83 is expressed at a high level in immunocompetent, activated and mature dendritic cells. Various pathogens can activate and modulate the function of dendritic cells. The presence of activated and mature dendritic cells in skin lesions of secondary syphilis has never been reported. In the present study, an immunohistochemical technique was used to determine the exact tissue distributions of CD83+ dendritic cells and interferon-gamma+ cells in skin lesions of patients with secondary syphilis. Immunohistochemical staining was performed by using formalin-fixed, paraffin-embedded sections. A small but significant subpopulation of CD83+ dendritic cells was found in the dermis. CD83+ dendritic cells were in close contact with lymphocytes. High-intensity staining of CD83 antigens was detected not only on the surface but also in the cytoplasm of dendritic cells. Infiltrating mononuclear cells were stained positively for CD4 or CD8, with CD8+ cells always being in the majority. A small number of interferon-gamma+ cells resembling mononuclear lymphoid cells were detected in all samples. These results provide in vivo support for the hypothesis that dendritic cells are activated by Treponema pallidum and that thus activated and mature CD83+ dendritic cells may play a role in the Th1 response in secondary syphilis.

Immunization with the N-terminal portion of Treponema pallidum repeat protein K attenuates syphilitic lesion development in the rabbit model

When used as an immunogen, Treponema pallidum repeat protein K (TprK) has been shown to attenuate syphilitic lesions upon homologous intradermal challenge in the rabbit model. To further explore this protein as a potential vaccine component, we sought to identify the immunogenic regions of TprK. The abilities of three recombinant peptides encompassing TprK to elicit T- and B-cell responses and to protect against challenge were examined. All three fragments elicited proliferative responses from splenocytes taken from infected rabbits. However, enzyme-linked immunosorbent assays indicated that only fragments 1 and 3 were consistently recognized by antisera from infected rabbits. Each fragment was also used to immunize rabbits that were subsequently challenged intradermally with infectious T. pallidum. All lesions on unimmunized control rabbits ulcerated and contained treponemes, while the lesions on rabbits immunized with fragment 1 were the least likely to have detectable treponemes (25%) and the least likely to ulcerate (37.5%). The lesions on rabbits immunized with fragment 3 showed intermediate results, and rabbits immunized with fragment 2 were the most likely of all those on immunized rabbits to have detectable treponemes (91.7%) and to ulcerate (66.7%). These results demonstrate that epitopes in fragment 1 are recognized by T cells and antibodies during infection and that immunization with this portion of TprK most effectively attenuates syphilitic lesion development.

The prozone phenomenon in secondary syphilis

We describe a 37-year-old woman with secondary syphilis, in whom the prozone phenomenon (false-negative test in undiluted specimens) occurred. The patient had been maintained on cyclosporine and prednisolone after renal transplantation. B-cell dysfunction induced by continuous immunosuppression may lead to higher non-treponemal serological titers. Non-treponemal testing should be repeated using serum dilutions to prevent missing the diagnosis of syphilis.

[Specific IgM tests in syphilis diagnosis]

A total of 359 sera of untreated patients with syphilis were examined by three methods for the detection of Treponema pallidum specific IgM antibodies, the 19S-IgM-FTA-ABS test, the IgM solid phase haemadsorption assay (IgM-SPHA), and the IgM Captia assay. The results were compared and evaluated. In primary syphilis, the 19S-IgM-FTA-ABS and IgM-captia yielded reactive results in all patients, whereas only 40% were positive in the IgM-SPHA; the corresponding values for early latent syphilis wee 96.0%, 89.8% and 73.1%, respectively. In secondary syphilis, the reactivity of one serum out of 27 was missed by IgM captia and that of another, by the IgM-SPHA. Mean values (ELISA units = extinction/cut-off) of IgM-captia were higher in primary (2.25) than in secondary syphilis (1.70). In neurosyphilis, only the IgM-SPHA test detected reactivity in all sera, sensitivity for 19S-IgM FTA-ABS and IgM-Captia was 50.0% and 23.1%, respectively. Specificity of the IgM-Captia test results, determined in 386 sera, was 91.2%. The results of specific IgM tests are essential in the diagnosis of congenital syphilis as well as in the recognition of reinfection; they indicate the need for treatment and are useful in the assessment of the effectiveness of therapy.

The localisation of treponemes and characterisation of the inflammatory infiltrate in skin biopsies from patients with primary or secondary syphilis, or early infectious yaws

OBJECTIVE

To study the localisation of treponemes and to analyse the inflammatory infiltrate in biopsy specimens from patients with primary or secondary syphilis, or early infectious yaws.

MATERIALS AND METHODS

Skin biopsies originating from human lesions of primary (29x) or secondary (15x) syphilis (Rotterdam), or early yaws (18x) (West Sumatra) were studied. Different histochemical and immunohistochemical detection methods were used in this study.

RESULTS AND CONCLUSION

The histochemical silver staining method according to Steiner revealed the presence of T. pallidum in all cases of primary syphilis studied. In 10 out of 14 cases of secondary syphilis, treponemes were demonstrated. With an immunofluorescence staining technique (IF) using anti-T. pallidum antiserum raised in rabbits (a-Tp), T. pallidum was demonstrated in 28 out of 29 cases of primary syphilis, and in 14 out of 14 studied cases of secondary syphilis. The silver staining method and IF showed identical localisations of T. pallidum (mainly in the dermal-epidermal junction zone or throughout the dermis). Using a-Tp antiserum in the indirect immunofluorescence technique, T. pertenue could be demonstrated in the dermis more often than with Steiner silver staining. However, epidermotropism of T. pertenue in yaws specimens was remarkable, compared with more mesodermotropism of T. pallidum; numbers of T. pertenue in the dermis were limited in all specimens. The dermal inflammatory infiltrate in primary and secondary syphilis was composed mainly of lymphocytes and plasma cells. In most cases more T (CD3 positive) cells than B (CD22 positive) cells were present. Regarding T cell subpopulations, in primary syphilis, T helper/inducer (CD4 positive) cells predominated in 86% of cases. In secondary syphilitic lesions, numbers of T helper/inducer cells were less frequent than or equal to T-suppressor/cytotoxic (CD8 positive) cells in 60% of cases. Remarkably, in yaws specimens the inflammatory infiltrate consisted mainly of IgG, but also IgA and IgM producing plasma cells. T or B lymphocytes were scarce, which is in sharp contrast with findings in syphilitic lesions.

Protracted Treponema pallidum-induced cutaneous chancres in rabbits infected with human T-cell leukemia virus type I

In a preliminary study, two of four rabbits infected with human T-cell leukemia virus type I (HTLV-I) demonstrated prolonged primary chancres following superinfection with Treponema pallidum, the causative agent of syphilis. Two rabbits inoculated with 1 x 10(7) HTLV-I-infected human MT-2 cells and two with infected rabbit cells from a line established in this laboratory (RLT-P), developed latent HTLV-I infection as detected by seroconversion 10 weeks after infection and by detection of HTLV-I sequences in the DNA of peripheral blood lymphocytes after amplification by polymerase chair reaction (PCR) 15 weeks after infection. The rabbits remained clinically normal and had normal blood counts. Six months after infection, the four HTLV-infected rabbits and two noninfected controls were challenged by the intradermal inoculation of 1 x 10(6) Treponema pallidum into eight sites on the shaved back. The lesions of two of the HTLV-I-infected rabbits had a time course similar to non-HTLV-I-infected controls and were completely healed by 4 weeks. The lesions of one of the other two rabbits with progressive disease began to heal about 7 weeks after T. pallidum challenge. The cutaneous lesions in the other rabbit remained dark-field positive and became a confluent eschar at 8 weeks; healing only after treatment with penicillin. Four months after the primary challenge none of the six rabbits previously challenged with T. pallidum had developed lesions after rechallenge and thus expressed chancre immunity. These results demonstrate that rabbits with latent HTLV-I infections may have defective cell-mediated immunity.

Rabbit model of disseminated syphilis: immunoblot and immunohistologic evidence for a role of specific immune complexes in lesion pathogenesis

Circulating immune complexes (CIC) containing Treponema pallidum proteins have been preliminarily implicated as inducers of a neutrophilic vascular reaction in early human cutaneous lesions of secondary syphilis. To clarify the role of specific CIC in producing cutaneous and renal lesions, 12 rabbits were studied at the following intervals after induction of disseminated syphilis: 20 days (4 rabbits: biopsies of normal and lesional skin for direct immunofluorescence (IMF) for (IgG, IgM, IgA, Clq, C3, C4), fibrin, and T. pallidum proteins; routine histology; and immunoblots of serum for CIC containing T. pallidum proteins); 21 days (4 rabbits: as at 20 days without IMF for T. pallidum protein); 23 days (4 rabbits: as at 20 days without IMF); 30 days (same 12 rabbits restudied with routine histology of normal and lesional skin; kidneys from 4 rabbits removed for routine, IMF, and electron microscopy (EM). Treponemal polypeptide antigen (MW-87 kd) was demonstrated in CIC from rabbits. Routine cutaneous histology showed evolution of lesions from an early neutrophilic vascular reaction to the typical lymphoplasmacytic reaction. IMF showed vessel-based immunoreactants in 3 of the 4 rabbits tested at 20 days and 1 of 4 at 21 days, and T. pallidum proteins in 3 of 4 rabbits at 20 days. Routine histology, IMF, and EM studies of glomeruli showed glomerular abnormalities, but no evidence of immune deposits containing specific T. pallidum protein. Skin and kidney studies of 4 controls were all negative. These data indicate a role for specific immune complexes in the pathogenesis of cutaneous lesions in this rabbit model.

Role of circulating immune complexes in human secondary syphilis

Studies in animal models and in the glomerulonephritis of human secondary syphilis and results from in vitro assays have suggested a role for circulating immune complexes (CICs) in human secondary syphilis. Nine adult subjects with early secondary syphilis were studied. All patients tested had CICs on C1q-binding or Raji cell assays. Proteins previously described as Treponema pallidum-specific antigens were detected by radioimmunoblot techniques in CICs from all five subjects tested. Biopsy of early cutaneous lesions revealed immunoreactants (IgG, C3, and/or C1q) in three of nine subjects and treponemal antigen in six of eight subjects tested. Histamine was injected intradermally as a trap for CICs, and biopsy of these injection sites revealed immunoreactants in four of nine subjects and treponemal antigen in five of eight subjects tested. A neutrophilic vascular reaction consistent with CIC-mediated vessel damage was seen in three of nine lesions and six of nine histamine injection sites. Normal controls did not show these changes.

Cutaneous secondary syphilis: preliminary immunohistopathologic support for a role for immune complexes in lesion pathogenesis

A circulating immune complex-mediated pathogenesis for lesions of secondary syphilis has been postulated. Textbook descriptions of a lymphoplasmacytic histopathologic picture have contradicted a role for circulating immune complexes in lesion pathogenesis. Four patients with early cutaneous lesions of secondary syphilis were studied. All four patients had serum Raji cell and/or Clq binding assay evidence for circulating immune complexes. Three patients showed a neutrophilic vascular reaction on histologic study of early lesions. The patients studied had immunofluorescence microscopic evidence of immunoreactant deposition in dermal blood vessels (4 hours) and/or a neutrophilic vascular reaction (24 hours) after intradermal histamine injection. Dieterle staining of lesional tissue from all patients showed the presence of treponemal organisms in dermal blood vessels. This new preliminary evidence adds some support to a circulating immune complex-mediated pathogenesis of cutaneous lesions in human secondary syphilis.

Acquired resistance and expression of a protective humoral immune response in guinea pigs infected with Treponema pallidum Nichols

Resistance to cutaneous syphilitic reinfection in strain 2 and strain 13 guinea pigs developed gradually 3 to 7 months after primary infection and reached maximum levels at 6 to 7 months after the induction of primary cutaneous disease. Associated with this acquired resistance was the occurrence of Arthus reactions and anamnestic-type antibody responses. Passive transfer of immune serum containing high-titered treponemal antibody into normal strain 2 guinea pigs significantly delayed the appearance and markedly diminished the severity and duration of skin lesions that developed after these recipients were challenged with treponemes but did not prevent the dissemination of organisms to the draining lymph nodes. These findings provide direct evidence that syphilitic infection elicits the formation of serum factors that are, at least, partially protective against symptomatic disease.

Adoptive transfer of anti-syphilis immunity with lymphocytes from Treponema pallidum-infected guinea pigs

Spleen and lymph node cells taken from strain 2 and strain 13 guinea pigs at the peak of their primary immune response to cutaneous syphilitic infection could transfer partial protection to symptomatic disease to normal syngeneic recipients challenged with the Nichols strain of Treponema pallidum. These recipients of immune cells had significantly fewer treponemes disseminating to the regional lymph nodes and developed fewer and less severe cutaneous lesions that resolved faster than those in guinea pigs that had been infused with normal lymphoid cells. Immune donor cells also had the capacity to transfer specific delayed-type hypersensitivity responses for T. pallidum antigens. Both T and B cells were effective in conferring anti-syphilis immunity which was associated with the almost immediate development and persistence of substantially elevated levels of circulating anti-treponemal antibody in the protected recipients. Our findings in this adoptive transfer system provide the first direct experimental evidence implicating both cellular and humoral components of the immune response as important effector mechanisms in host resistance to the pathogenic spirochete causing venereal syphilis.

[Diagnosis and therapy of syphilitic changes of the skin and mucous membrane in the head and neck]

Since the mid seventies the German Federal Board of Statistics has recorded a decrease in the incidence of the classical venereal diseases gonorrhoea and syphilis. This decrease is based only on a decline in the morbidity of gonorrhoea. Statistics on syphilis show an increase, from about 6000 to 8900 new cases each year, that is an increase of 48% between 1974 and 1978. Some cities such as Cologne, with a total of 401 new cases each year, show an increase, while numbers in rural regions remain unchanged or show a slight decline. Between 1978 and 1980 at the ENT and Dermatologic OPC of Cologne University many ulcers of uncertain aetiology in the head and neck region have been diagnosed as primary or secondary syphilis or as unusual presentations of this disease. In our Department a primary lesion of the head and neck was the presenting symptom in about 6% of all newly diagnosed cases. The differential diagnosis of early syphilitis lesions in the head and neck, the present position of serological diagnosis, and the current treatment of syphilis are illustrated by selected typical lesions.

[Tertiary syphilis of the skin with biologic false negative 19S-(IgM-)FTA-ABS test]

A report is presented of a patient with tertiary syphilis of the skin with biologically false negative 19S-(IgM-)FTA-ABS-test. This possibility of failure in this otherwise highly reliable test for the detection of specific 19S-(IgM-)antibodies is still little known.

Immune complexes in experimental syphilis: a methodologic evaluation

Sustained antigenic stimulation following intravenous infection of rabbits with Treponema pallidum results in antibody responses and the formation of immune complexes. Complexes in greater than 300 sera from normal rabbits and from animals with experimental syphilis were measured by Raji cell and polyethylene glycol-complement consumption assays. Profound increases in both the incidence and levels of immune complexes were seen between the third and seventh weeks of infection. Single radial immunodiffusion studies revealed moderate increases in immunoglobulin levels and depression of C3 levels during the third and fourth weeks of infection. Penicillin treatment was followed by normalization of C3 levels and clearance of immune complexes. Lower levels of complexes in the sera of intradermally infected rabbits and the absence of immune complexes in intratesticularly infected animals suggest that immune complexes in the circulation may be related to the extent and severity of cutaneous involvement.

Jarisch-Herxheimer reaction in complement-depleted rabbits. Histological and immunofluorescence studies of early cutaneous lesions

The possible role of complement in the pathogenesis of the Jarisch-Herxheimer reaction was assessed in cutaneous syphilitic lesions in two groups of rabbits treated with penicillin; in one group complement was depleted before penicillin therapy. Serial biopsy specimens were similar histologically in both groups. The activation of the complement pathways did not seem to play a role in the pathogenesis of early cutaneous syphilitic lesions in rabbits during the Jarisch-Herxheimer reaction.

Host response to Treponema pallidum in intradermally-infected rabbits: evidence for persistence of infection at local and distant sites

Intradermal infection of rabbits with Treponema pallidum imitiates rapid and active cellular response at the site of injection. During the first 2 weeks following infection, there is a marked increase in the numbers of organisms at the site of infection. Systemic dissemination of treponemes occurs during the early stage of infection, presumably before the immune response is fully mobilized. The mononuclear infiltration, which is apparent at the lesion site one week postinfection, becomes more pronounced at 2 weeks. The infiltrating cells are predominantly T lymphocytes and macrophages. By 4 weeks postinfection, most of the organisms have been cleared from the primary site; however, low numbers of treponemes survive locally and in distant tissues. Thus, whereas infection with T. pallidum appears to activate immune mechanisms which are capable of clearing most of the organisms from the primary lesion, some organisms are able to evade these mechanisms and persist in vivo.

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.

Detection by direct immunofluorescence of antibodies to Treponema pallidum in the cutaneous infiltrates of rabbit syphilomas

By direct immunofluorescence, with use of fluorescein-labeled sonified Treponema pallidum, specific antibodies were detected in the tissue infiltrates of cutaneous syphilomas in rabbits. Specimens from cutaneous and mucosal inflammatory lesions induced by intradermal injection of a keratinous substance from an epidermal cyst served as controls. Granular fluorescence was detected in the dermis of 11 of the 12 syphiloma specimens and corresponded to areas of heavy plasma cell infiltrates, and some fluorescence was found directly on plasma cells identified by subsequent staining with hematoxylin and eosin. This fluorescence could be blocked by preabsorption. Control slides did not show any fluorescence. Immunopathologic techniques using labeled antigens may be of diagnostic value in syphilis and other infectious disorders which feature specific infiltrates.

Demonstration by labeled treponemal antigen of specific antibodies in the tissue infiltrates of secondary syphilis

Specific antitreponemal antibodies have been demonstrated by immunofluorescence techniques in the lymphoplasmocytic infiltrates which characterize early symphilitic lesions. A purified suspension of Nichols strain Treponema pallidum was sonified and labeled with fluorescein isothiocyanate and applied to cryostat sections of 12 biopsy specimens from the cutaneous lesions of 11 patients with proven secondary syphilis, using a modified direct immunofluorescence procedure. Specimens from various inflammatory dermatoses processed similarly served as controls. Granular fluorescence was noted in the dermis in 9 of the 12 specimens corresponding to areas of heavy plasma cell infiltration and some fluorescence was found directly on plasma cells which were identified by subsequent hematoxylin and eosin staining. This fluorescence could be blocked by prior incubation of the sections with unlabeled sonified treponemal suspension. Control slides did not reveal any fluorescence. The use of labeled treponemal antigen may aid the tissue diagnosis of early syphilitic lesions which can mimic a variety of dermatological disorders.

Reinfection primary and secondary syphilis: the post treatment serologic response

It has long been observed that patients with reinfection primary and secondary syphilis have a slower serologic response to treatment than those with an initial infection. The case records of three patients with reinfection primary and seven patients with reinfection secondary syphilis were examined and confirmed the clinical observation.