CD55 characterizes regulatory T cells with reduced functionality and is downregulated in rheumatoid arthritis.

Objective: This study aimed to investigate the role of CD55 in regulatory T cells (Tregs) and clarify its clinical relevance in rheumatoid arthritis (RA).

Methods: Flow cytometry was used to examine the expression of Helios and CTLA-4 in CD55 + and CD55- Tregs in mouse peripheral blood and spleen. FoxP3 mice were employed to analyze the in vitro inhibitory function of CD55 + and CD55-Tregs. We compared CD55 expression and function in control and CIA mice. Additionally, the expression of Helios, PD-1, and TIGIT in CD55 + Tregs was examined in healthy controls and RA patients. Correlation analysis and receiver operating characteristic (ROC) curves were used to assess the clinical utility of CD55-related T cell subgroups in RA diagnosis.

Results: High CD55 expression was observed in CD4 + T cells and Tregs, with significantly higher levels in peripheral blood than in the spleen in mice. CD55-Tregs exhibited increased expression of Helios and CTLA-4, and a more pronounced suppressive function compared to CD55 + Tregs in mice. Additionally, CD55 expression in Tregs from peripheral blood and spleen of CIA mice was significantly reduced. In humans, peripheral blood CD55- Tregs expressed higher levels of Helios and TIGIT. Moreover, CD55 + Tregs were markedly reduced in RA patients and correlated with clinical indicators of RA, demonstrating potential as diagnostic markers.

Conclusions: CD55 + Tregs represent a subset of Tregs with weaker functionality and were decreased in RA and could assist the diagnosis of RA.