The Role of IL-2/Anti IL-2 Antibody Complex in Regulatory T Cell Recruitment and Corneal Allograft Survival

Abstract

Purpose: : To determine the role of IL-2/Anti IL-2 antibody complex (IL-2-complex) in the expansion and recruitment of regulatory T cells (Tregs), and its role in corneal allograft survival.

Methods: : In order to test the in vivo expansion of Tregs induced by IL-2-complex treatment, intraperitoneal injections of IL-2-complex at a concentration of 2% of IL-2 and 1% of Anti IL-2 or control sterile PBS, were given to C57BL/6 (H-2b) mice at day 0 and day 2. Lymphoid tissue was harvested four days after treatment for flow cytometry analysis using CD4, CD25 and Foxp3 markers. Expansion of Tregs was calculated in lymph nodes and spleen. To determine if IL-2-complex in vivo expansion of Tregs could induce immunological "protection", fully MHC mismatch corneal allotransplants were performed, using Balb/c (H-2d) mice as donors on IL-2-complex treated C57BL/6 (H-2b) mice recipients. Graft survival was monitored using Holland's Criteria, and lymph nodes were harvest for flow cytometry analysis as previously described. Furthermore, to assess a correlation between Tregs recruitment to the site of transplantation and graft survival, Foxp3-IRES-mRFP C57BL/6 (FIR) mice were used as recipient and the in vivo influx of Tregs into the site of transplantation was measured using real time steremicroscopy fluorscecent analysis.

Results: : Flow cytometry demonstrated an increase expansion of CD4+, CD25+ FoxP3 + cells in the lymph nodes and spleen of IL-2-complex treated animals in contrast to PBS treated control. Moreover, corneal allograft recipients had a decreased rate of rejection after complex injection. In vivo imaging of allotransplants in FIR mice recipients, shows that Tregs are present at the site of transplantation earlier, as soon as day 1 after transplantation compare to the control group were Tregs arrive at day 3 . However imaging at later time points showed no difference in the presence of Tregs in both groups.

Keywords: immunomodulation/immunoregulation • immune tolerance/privilege • transplantation