[Effects of exogenous interleukin-2, interleukin-23 on differentiation of IRBP 1-20-specific T cells toward Th1 and Th17 and comparison of the pathogenicity of IRBP 1-20-specific T cells].

OBJECTIVES

To explore the effects of exogenous interleukin (IL)-2 and IL-23 on differentiation of IRBP 1-20-specific T cells originated from C57BL/6 mouse with experimental autoimmune uveitis (EAU) and to investigate the difference in pathogenicity.

METHODS

Experimental study. Thirty C57BL/6 mice were immunized subcutaneously with 200 µl emulsion containing 200 µg interphotoreceptor retinoid-binding protein (IRBP) 1-20 and 0.8 mg mycobacterium tuberculosis in complete Freund's adjuvant, distributed over six spots at the tail base and on the flank. On postimmunization Day 13, spleens and draining lymph nodes were removed from mice, and a part of spleens, as the control group, was reserved for examining the expression of IFN-γ mRNA and IL-17 mRNA by RT-PCR. T cells were isolated from the rest of spleens and lymph nodes by passage through a nylon wool column, and then T cells were stimulated for 48 hours with IRBP 1-20 in the presence of antigen-presenting cell and mouse recombinant cytokine IL-2 or IL-23. The IRBP 1-20-specific T cells were separated by Ficoll gradient centrifugation, the expressions of IFN-γ mRNA and IL-17 mRNA were assessed by RT-PCR, and IFN-γ and IL-17 in T cells supernatant were detected using a commercial ELISA kit. The T cells were cultured for another 48 hours, and then the proportions of IL-17(+)γδ(+)T cells were analyzed by flow cytometry. EAU models were built in 30 C57BL/6 mice, T cells from which were randomly divided into two groups according to the methods mentioned above: IL-2 group and IL-23 group. Transfer EAU models were built in other 6 mice and divided into two groups, IL-2 group and IL-23 group, by intraperitoneal injection of 3.5×10(6) IRBP-special-T cells from IL-2 group or IL-23 group respectively. Clinical changes were observed by indirect ophthalmoscopy on postimmunization day 3, 7, 14. For histopathological evaluation, whole eyes were collected on postimmunization day 21. Rank sum test, one-way ANOVA and paired t test were used to analyze the results. A comparison of pathogenicity was made between Th1 and Th17 through clinical observation and histopathological evaluation of B6 mouse.

RESULTS

Rosette formation was found among T cells on poststimulation day 2. There was a statistical difference in the expression of IFN-γ mRNA between the IL-2 group and normal group or IL-23 group (0.26 ± 0.02 vs. 0.12 ± 0.05 or 0.10 ± 0.00) (F = 80.51, P = 0.003); however, the expression of IFN-γ in the IL-2 group [(13 124.67 ± 107.73) µg/L] was higher than that of the IL-23 group [(3953.67 ± 117.34) µg/L] (t = 169.61, P = 0.000); and the expression of IL-17 mRNA in the IL-2 group [(588.67 ± 77.43) µg/L] was lower than that of the IL-23 group [(5038.33 ± 88.00) µg/L] (t = -361.71, P = 0.000). Flow cytometer showed that the concentration of IL-17 in the IL-2 group [(3.23 ± 0.28)%] was significantly lower than that in the IL-23 group [(9.93 ± 0.55)%] (t = -33.18, P = 0.001). There was a significant difference in the proportion of IL-17(+)γδ(+)T cells between the IL-23 group and IL-2 group (9.93 ± 0.55 vs. 3.23 ± 0.28) (t = -33.18, P = 0.001). Inflammatory response could not be detected in either group three days after injection of IRBP 1-20-specific T cells. Both groups of mice had the most severe inflammatory response on the 14 th day, of which that of the IL-23 group was significantly more severe.

CONCLUSIONS

IL-23 facilitates IRBP 1-20-specific T cells to differentiate into Th17, whereas IL-2 inhibits this process and induces these cells to differentiate towards Th1. Further studies showed that the pathogenicity of Th17 cells was significantly higher than that of Th1 cells.