Track: Basic Science

Abstract:

Rubella virus (RuV) has been increasingly recognized as a potential antigenic trigger in suppurative and inflammatory granulomatous dermatitis.¹ These granulomas consist of aggregates of macrophages and brisk lymphocytic infiltrate in which RuV antigens have been detected. These granulomatous lesions may persist for years, often refractory to conventional therapies. Immunohistochemical and molecular techniques can identify RuV within lesional tissue, enhancing diagnostic accuracy and enabling tailored clinical management. ² Our aim was to delineate the lymphocytic infiltrate present in RuV-associated granulomas using immunohistochemistry-based (IHC) staining.

We compared 32 granulomatous cases in our study, 22 of which were RuV-positive by fluorescent immunohistochemistry (IHC) with rubella capsid antibody and 10 that were RuV-negative. Overall, RuV-positive granulomatous dermatitis had more lymphocytes compared to negative granulomas (95% and 44% respectively, p=0.004) and contained a higher proportion of CD8 cytotoxic T cells, whereas CD4 T cells predominated in RuV-negative granulomas. CD163 demonstrated larger granulomas in RuV-positive granulomas compared to negative. Staining for CD20 and CD56 was negative among most cases, regardless of positivity,

These findings highlight distinct immunologic patterns that may differentiate RuV-positive from RuV-negative granulomatous dermatitis. While molecular testing remains essential for definitive diagnosis, IHC staining can serve as a tool for cases that should be considered for RuV and supporting the role of cytotoxic T-cell responses in RuV-driven granulomatous disease.

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Rachel Tao