Objective: To evaluate the effects of cytokines on the proliferation and function of CD4+ CD25+ regulatory T cell (Treg).
Methods: Tregs were isolated from naive C57BL/6 mice spleen and lymph nodes. Mature dendritic cells (mDC) were isolated from DBA/2 mice, co-cultured with Tregs, and divided into 4 groups with or without interleukin-2 (IL-2), interleukin-4 (IL-4), and interleukin-15 (IL-15) added into the culture fluid. Fluorescence-activated cell sorting (FACS) was used to detect the Treg proliferation and apoptosis with CFSE and annexin-V staining. The co-culture increased Tregs were divided into 5 groups: CFSE labeled naïve CD4+ CD25- T cells, self-proliferated Treg, Treg mixedly cultured with IL-2 mDC, and Teff, Treg mixedly cultured with IL-4, mDC, and Teff, and Treg mixedly cultured with IL-15, mDC, and Teff, a control group included Teff co-cultured with mDC. FACS was used 5 d later to evaluate the suppressive function of the Treg on the Teff. The expression of Foxp3, indicating the phenotype of Treg was detected.
Results: FASC showed that the values of precursor frequency (PF) of the Tregs stimulated by IL-2, IL-4, and IL-15 were 31.3%, 28.9%, and 34.5% respectively, all significantly higher than that of the control group (14.5% all P < 0.05), and the values of proliferation index (PI) of the Tregs stimulated by IL-2, IL-4, and IL-15 were 1.9, 1.7, and 1.8 respectively, all significantly higher than that of the control group (1.5, all P < 0.05). The apoptotic rates of the Tregs stimulated by IL-2, IL-4, and IL-15 were 12. 8% , 11.4%, and 12.7% respectively, all significantly lower than that of the control group (28.9%, P < 0.05). The Foxp3 expression rate of the Tregs stimulated by IL-2, IL-4, and IL-15 was 91.75%.
Conclusion: IL-2, IL-4, and IL-15 in the in vitro culture of Treg stimulate the Treg proliferation, reduce their apoptosis, and maintain their suppressive function. The proliferated Tregs still maintain their phenotype, highly expressing Foxp3.