CD55hi MAIT cells with elevated cytokine secretion and activation markers serve as potential diagnostic indicators in Sjögren's disease.

Mucosal-associated invariant T (MAIT) cells play a vital role in immune responses, yet their involvement in autoimmune diseases such as Sjögren's disease (SjD) remains unclear. CD55, a key regulator of complement activation, influences immune cell function. This study investigates CD55 expression on MAIT cells in SjD patients and healthy controls, evaluating its potential as a diagnostic marker. Flow cytometry was used to assess CD55 expression on MAIT cell subsets, including CD4-CD8+, CD4+CD8-, double-positive (DP), and double-negative (DN), in peripheral blood from SjD patients and healthy controls. Functional markers (PD-1, CD83, and CD44), cytokine production (TNF-α, IFN-γ, IL-17, IL-22), and granzyme B (GZMB) secretion were analyzed following 5-OP-RU and brefeldin A stimulation. Receiver operating characteristic (ROC) analysis was conducted to evaluate the diagnostic utility of CD55 expression. CD55 was highly expressed on MAIT cells, with the highest expression intensity observed in DP MAIT cells, followed by CD4+CD8- MAIT and CD4-CD8+ MAIT, with the lowest expression found in DN MAIT cells. CD55hi MAIT cells demonstrated significantly higher percentages of PD-1+, CD83+, and CD44+ cells, along with enhanced cytokine and GZMB secretion following stimulation. In SjD patients, CD55 expression was significantly upregulated in MAIT cells. ROC analysis indicated that CD55hi MAIT cells have potential diagnostic value for SjD. CD55 is highly expressed on MAIT cells, with upregulation in SjD patients correlating with inflammation and autoantibodies, suggesting CD55hi MAIT cells as a potential diagnostic marker for SjD.