Immunostaining for Treponema pallidum: Caution in its Evaluation

Round Bodies Detected by Treponema pallidum Immunohistochemical Stain in Two Cases of Cutaneous Syphilitic Gummata

ABSTRACT

Tertiary syphilis may present a diagnostic challenge due to negative nontreponemal serologies in up to 30% of cases and frequent lack of identifiable spirochetes on histopathology or other direct detection tests. We report 2 cases of round bodies staining with Treponema pallidum immunohistochemistry by light microscopy in biopsies from cutaneous syphilitic gummata. In 1 case, the finding was validated 3 times by 2 independent laboratories; in the other case, T. pallidum was detected by polymerase chain reaction in the biopsy sample. Spirochete round bodies have previously been reported in the setting of electron microscopy and fluorography, but to the best of our knowledge, have not been reported by light microscopy in a routine skin biopsy. Although the clinical implications are unclear, this may represent a helpful new paradigm for the diagnosis of tertiary syphilis.

Granulomatous Secondary Syphilis: A Case Report with a Brief Overview of the Diagnostic Role of Immunohistochemistry

The diagnosis of syphilis can be challenging for dermatologists and dermatopathologists. In particular, secondary syphilis can have different clinical and histopathological presentations. A granulomatous tissue response is an unusual finding in secondary syphilis. We report the case of a 77-year-old man who presented with a 4-week history of non-pruritic generalised macules, papules, nodules and plaques. Histopathologically, there was a dense perivascular and periadnexal lympho-histiocytic dermal infiltrate with non-palisading and non-caseifying epithelioid granulomas and abundant plasma cells. The diagnosis of syphilis was confirmed by serology and immunohistochemical detection of Treponema pallidum in the biopsy specimen. A brief overview of the diagnostic role of immunohistochemistry is also provided, with particular emphasis on reported cases of granulomatous secondary syphilis.

Immunohistochemical diagnosis of human infectious diseases: a review

BACKGROUND

Immunohistochemistry (IHC) using monoclonal and polyclonal antibodies is a useful diagnostic method for detecting pathogen antigens in fixed tissues, complementing the direct diagnosis of infectious diseases by PCR and culture on fresh tissues. It was first implemented in a seminal publication by Albert Coons in 1941.

MAIN BODY

Of 14,198 publications retrieved from the PubMed, Google, Google Scholar and Science Direct databases up to December 2021, 230 were selected for a review of IHC techniques, protocols and results. The methodological evolutions of IHC and its application to the diagnosis of infectious diseases, more specifically lice-borne diseases, sexually transmitted diseases and skin infections, were critically examined. A total of 59 different pathogens have been detected once in 22 different tissues and organs; and yet non-cultured, fastidious and intracellular pathogens accounted for the vast majority of pathogens detected by IHC. Auto-IHC, incorporating patient serum as the primary antibody, applied to diseased heart valves surgically collected from blood culture-negative endocarditis patients, detected unidentified Gram-positive cocci and microorganisms which were subsequently identified as Coxiella burnetii, Bartonella quintana, Bartonella henselae and Tropheryma whipplei. The application of IHC to ancient tissues dated between the ends of the Ptolemaic period to over 70 years ago, have also contributed to paleomicrobiology diagnoses.

CONCLUSION

IHC plays an important role in diagnostic of infectious diseases in tissue samples. Paleo-auto-IHC derived from auto-IHC, is under development for detecting non-identified pathogens from ancient specimens.

Immunohistochemistry in the diagnosis of cutaneous bacterial infections

The identification of pathogens is of vital importance for the adequate treatment of infections. During the past 2 decades, the approach to histopathologic diagnosis has been dramatically transformed by immunohistochemistry (IHC) specifically in the diagnosis and classification of tumors and more recently in the diagnosis of infectious diseases in tissue samples. The main goals of this article were to: (1) identify by IHC the cutaneous structures where bacterial pathogens are expressed in the course of infection, (2) identify the specific cells in which bacterial pathogens are expressed in positive cases, and (3) describe the pattern of distribution of the bacterial antigens within these cells (nuclear, cytoplasmatic, or membranous). This article is an up-to-date overview of the potential uses and limitations of IHC in the histopathologic diagnosis of cutaneous bacterial infections. In conclusion, IHC is especially useful in the identification of microorganisms that are present in low numbers, stain poorly, are fastidious to grow, culture is not possible, or exhibit an atypical morphology.

Fluorescence in situ hybridization for the identification of Treponema pallidum in tissue sections

Syphilis is often called the great imitator because of its frequent atypical clinical manifestations that make the disease difficult to recognize. Because Treponema pallidum subsp. pallidum, the infectious agent of syphilis, is yet uncultivated in vitro, diagnosis is usually made using serology; however, in cases where serology is inconclusive or in patients with immunosuppression where these tests may be difficult to interpret, the availability of a molecular tool for direct diagnosis may be of pivotal importance. Here we present a fluorescence in situ hybridization (FISH) assay that simultaneously identifies and analyzes spatial distribution of T. pallidum in histological tissue sections. For this assay the species-specific FISH probe TPALL targeting the 16S rRNA of T. pallidum was designed in silico and evaluated using T. pallidum infected rabbit testicular tissue and a panel of non-syphilis spirochetes as positive and negative controls, respectively, before application to samples from four syphilis-patients. In a HIV positive patient, FISH showed the presence of T. pallidum in inguinal lymph node tissue. In a patient not suspected to suffer from syphilis but underwent surgery for phimosis, numerous T. pallidum cells were found in preputial tissue. In two cases with oral involvement, FISH was able to differentiate T. pallidum from oral treponemes and showed infection of the oral mucosa and tonsils, respectively. The TPALL FISH probe is now readily available for in situ identification of T. pallidum in selected clinical samples as well as T. pallidum research applications and animal models.