Study of Circulating Natural Antibodies Against CD25 and FOXP3 in Type-2 Diabetes.

Background: Natural antibodies are critical components for maintaining homeostasis of the immune system. Regulatory T (Treg) cells have indispensable effects on immunosuppressive function and peripheral immune tolerance. Both CD25 and FOXP3 are specifically expressed in Treg cells and their natural antibodies may protect against the development of type-2 diabetes (T2D). The present study aimed to test whether circulating antibodies against CD25 and FOXP3 were altered in first-episode patients with T2D. Methods: An enzyme-linked immunosorbent assay (ELISA) was developed in-house to detect the levels of plasma IgG antibodies against five linear peptide antigens with three derived from CD25 (named CD25a, CD25b, CD25c) and two derived from FOXP3 (called FOXP3a and FOXP3b) among 200 first-episode patients with T2D and 220 healthy controls. Results: Mann-Whitney U test showed a significant decrease in anti-CD25a IgG levels in patients with T2D as compared with the healthy controls (Z = -3.438, p = 0.0006), male patients mainly contributing to the decreased levels of anti-CD25a IgG levels (Z = -3.065, p = 0.002). The other four IgG tests demonstrated a lower level of plasma IgG antibodies in the patient group than the control group, but failed to show statistical significance (p > 0.01). ROC curve analysis indicated that the anti-CD25a IgG assay had the best sensitivity of 19.5% against the specificity of 90%. Conclusions: Decreased anti-CD25 IgG levels in the circulation may represent a reduction in the number of Treg cells and detection of such antibodies may be beneficial to the understanding of immunological changes in T2D patients.