Prominent contribution of Th1, Th17, and Tregs to the host response during M. neoaurum infection

M.neoaurum infection increased the inhibitory function of Tregs and the death rate associated with Salmonella coinfection

Mycobacterium neoaurum belongs to the nontuberculous mycobacteria (NTM) and is ubiquitously present in the environment. However, the changes in Treg percentages and suppressive properties in mice infected with M. neoaurum are still not elucidated. In this study, mice were intraperitoneally injected with M. neoaurum. The change in the CD4⁺CD25⁺ Treg cell percentage in the spleen was analyzed using flow cytometry. There was a significant increase in the number of CD4⁺CD25⁺ cells by week 6 postinfection, with a peak proportion of approximately 2%. The Foxp3 and IL-10 mRNA expression in CD4⁺CD25⁺ cells from the spleens of M.neoaurum-infected mice was higher than that in CD4⁺CD25⁺ cells from the spleens of noninfected controls. Proliferation suppression assay results indicated that CD4⁺CD25⁺ cells suppressed the proliferation of CD4⁺CD25^- cells at week 6 after M.neoaurum infection, and the suppression rate reached 89.8%. However, CD4⁺CD25⁺ cells from the noninfected control group did not suppress the proliferation of CD4⁺CD25^- cells. Based on the above results, mice were subjected to oral administration of S. Typhimurium at 6 weeks postinfection with M. neoaurum, and we found that the mortality of the M.neoaurum-S. Typhimurium infection group was higher than that of the S. Typhimurium infection group. In addition, serious pathological changes appeared in the liver and cecum of the M.neoaurum-S.Typhimurium infection group compared with those of the S. Typhimurium infection group. M. neoaurum increased Treg percentages and suppressed spleen function in mice. These results revealed the possibility that persistent M.neoaurum infection could increase the occurrence of secondary infection.

Interleukin-35 mitigates the function of murine transplanted islet cells via regulation of Treg/Th17 ratio

Pancreatic islet transplantation is a promising treatment for type 1 diabetes (T1D). Interleukin-35 (IL-35) is a recently discovered cytokine that exhibits potent immunosuppressive functions. However, the role of IL-35 in islet transplant rejection remains to be elucidated. In this study, we isolated islet cells of BALB/c mouse and purified CD4+ T cell subsets of a C57BL/6 mouse. The model for islet transplantation was established in vitro by co-culture of the islet cells and CD4+ T cells. IL-35 (20 ng/ml) was administered every other day. Following co-culture, the islet function and Treg/Th17 ratio were analyzed on days 1, 3, and 5. Furthermore, the Th17/Treg ratio was modulated (1:0–2), and the function of islet cells as well as proliferation of Th17 cells were analyzed. T cell sorting was performed using the magnetic bead sorting method; Treg and Th17 count using flow cytometry; cell proliferation detection using the carboxyfluorescein diacetate succinimidyl ester (CFSE) method, and islet function test using the sugar stimulation test. Results showed that Th17 counts increased in the co-culture system. However, after administration of IL-35, the number of Treg cells increased significantly compared to that in the control group (50.7% of total CD4+ T cells on day 5 in IL-35 group vs. 9.5% in control group) whereas the proliferation rate of Th17 cells was significantly inhibited (0.3% in IL-35 group vs. 7.2% in control group on day 5). Reducing the Th17/Treg ratio significantly improved the function of transplanted islets. Treg inhibited Th17 proliferation and IL-35 enhanced this inhibitory effect. IL-35 mitigates the function of murine transplanted islet cells via regulation of the Treg/Th17 ratio. This might serve as a potential therapeutic strategy for in-vivo islet transplant rejection and T1D.