Immunohistochemical Analyses of Skin Lesions with Monkeypox Virus A29 and A35 Antibodies: A Novel Insight for Clinical-Histopathological Forms.

The aim of this study was to describe the clinical, histopathological, and immunohistochemical characteristics of monkeypox (MPX) and offer meaningful insights into the clinicopathological characteristics. Eight males who have sex with males and were diagnosed with MPX based on positive results from MPX virus (MPXV)-specific polymerase chain reaction were recruited. Skin biopsies were obtained from four selected lesions, including typical and atypical forms. Histopathological examinations of atypical solitary ulceration revealed infiltrating inflammatory cells, predominantly plasma cells and lymphocytes forming a "sleeve" around the superficial vessels of the dermis. These features may be misinterpreted as indicative of cutaneous syphilis. In addition, typical pustular lesions had a central necrotic epidermis accompanied by a perivascular inflammatory infiltrate dominated by neutrophils, as well as ballooning and reticular degeneration of keratinocytes. Additionally, multinucleated keratinocytes and eosinophilic cytoplasmic inclusions (Guarnieri bodies) were observed. Importantly, this study represents a pioneering report on the immunohistochemical localization of MPXV A29 and A35 proteins in skin lesions, distinguishing it from previous studies that focused on detecting vaccinia virus proteins. The anti-MPXV A29 antibody had intense cytoplasmic staining, specifically within the affected keratinocytes in the adjacent epidermis and hair follicles, thereby contributing to the diagnosis of MPX, particularly in individuals with atypical skin lesions.