Background: Mixed connective tissue disease (MCTD) with a range of clinical manifestations and is recognized as an independent disease with similarities to systemic lupus erythematosus (SLE) and systemic sclerosis (SSc), or as an early manifestation of these conditions. In SLE, there is an imbalance in Th1/Th2 and Th17/Treg[1,2], activation of B cells in CD4+T cell subsets[3], and abnormal activation of CD4+T cells, as well as skin tissue infiltration and Th2/Th17 immune bias in SSc[4]. However, there is limited research on CD4+T cell subsets in MCTD, and the characteristics of these subsets are not well understood. Furthermore, cytokines such as IL-10 have been found to be closely associated with MCTD and play a significant role in its onset and progression.

Objectives: We conducted an analysis of the peripheral blood lymphocyte subsets, CD4+T cell subsets, and related cytokines in these three disease groups and healthy controls in order to uncover the immune differences and characteristics between MCTD and SLE, SSc. Furthermore, we aimed to explore the relationship between the related cytokines IL-2 and IL-10 and MCTD.

Methods: 48 patients with MCTD, 51 patients with SLE, 35 patients with SSc and 49 with HCs were enrolled in this research. The absolute counts of peripheral blood lymphocyte subsets and CD4 ⁺ T cell subsets were examined using flow cytometry, and serum cytokine levels were measured using flow cytometry microbead arrays.

Results: Absolute counts of T cells, CD4 ⁺ T cells, CD8 ⁺ T cells, NK cells, Th1 cells, Th2 cells, and Treg cells were decreased in the MCTD group compared to the HC group (P<0.05). The absolute counts of CD4 ⁺ T cells, Th1 cells, and Th2 cells were reduced in the MCTD group compared to the SSc group (P<0.05), and there was no significant difference compared to the SLE group. Cytokines (IL-2, IL-4, IL-6, IL-10, IL-17, IFN-γ, TNF-α) levels were significantly higher in the MCTD group compared to the HC group and the SSc group (P<0.05), and there was no significant difference in cytokines compared to the SLE group. Further analysis revealed that cardiac enzymes (CK, CK-MB, AST, α-HBDH, LDH) were positively correlated with cytokines (IL-2, IL-4, IL-6, IL-10, IL-17, IFN-γ, TNF-α) in MCTD (P<0.05). In addition, we found that IL-2 was associated with disease activity in MCTD and IL-10 was associated with myoinflammatory symptoms in MCTD, the area under the ROC curve (AUC) was 0.745 (95% CI 0.576-0.915, P=0.0116).

Conclusion: Our investigation uncovered immunological variances in peripheral blood lymphocyte subgroups, CD4+T cell subgroups, and cytokines among MCTD, SLE, SSc, and healthy controls. Furthermore, we emphasized that cytokines in MCTD are linked with cardiac enzymes, and IL-2 is correlated with disease activity. IL-10 can serve as an autonomous risk factor and predictor of myoinflammatory symptoms in MCTD, laying the groundwork for further exploration into the potential pathogenesis of MCTD.

REFERENCES: [1] Shan J, Jin H, Xu Y. T Cell Metabolism: A New Perspective on Th17/Treg Cell Imbalance in Systemic Lupus Erythematosus [J]. Front Immunol, 2020, 11: 1027.

[2] Dolff S, Bijl M, Huitema M G, et al. Disturbed Th1, Th2, Th17 and T(reg) balance in patients with systemic lupus erythematosus [J]. Clin Immunol, 2011, 141(2): 197-204.

[3] Long D, Yang B, Yang M, et al. Bach2 in CD4(+) T cells from SLE patients modulates B-cell differentiation and IgG production [J]. Eur J Immunol, 2023, 53(4): e2250109.

[4] Maehara T, Kaneko N, Perugino C A, et al. Cytotoxic CD4+ T lymphocytes may induce endothelial cell apoptosis in systemic sclerosis [J]. Journal of Clinical Investigation, 2020, 130(5): 2451-2464.

Acknowledgements: NIL.

Disclosure of Interests: None declared.