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A New Model of Chronic Colitis in SCID Mice Induced by Adoptive Transfer of CD62L+ CD4+ T Cells: Insights into the Regulatory Role of Interleukin-6 on Apoptosis

Objective: The proinflammatory cytokine interleukin (IL)-6 is involved in various chronic inflammatory processes. IL-6 is a predominant cytokine produced by lamina propria T cells in Crohn’s disease and experimental colitis. This study was designed to examine the effect of a neutralizing IL-6-receptor (IL-6R) antibody on the programmed cell death of mucosal T cells in the CD62L+ CD4+ SCID transfer model of chronic experimental colitis in mice and to gain more insight into the pathogenesis of this transfer colitis model. Methods: For adoptive transfer, we isolated CD62L+ CD4+ double-positive T cells from wild-type BALB/c mice followed by intraperitoneal application of 1 million cells in CB17 SCID mice. The purity of the transferred T-cell population was tested by FACS analysis. Cytokine secretion was measured by ELISA. Western blot analysis was performed to detect phospho-STAT-3 in protein extracts of splenic cells. Cryo- and paraffin colon cross-sections were used to perform immunochemical or fluorescence TUNEL stainings. Results: We isolated CD62L+ CD4+ and CD62L– CD4+ T cells. In vitro studies showed an increased production of IL-4 by CD62L– CD4+ T cells compared to CD62L+ T cells. 8–10 weeks after transfer of CD62L+ CD4+ T cells in SCID mice, reconstituted mice developed wasting disease, anal prolapse and diarrhea, whereas mice reconstituted with CD62L– CD4+ did not, similar to anti-IL-6R-treated CD62L+ CD4+-reconstituted SCID mice. Anti-IL-6R-treated reconstituted SCID mice showed decreased levels of activated STAT-3. The previously described efficacy of anti-IL-6R antibody treatment on colitis activity appeared to be due to the induction of apoptosis, as many TUNEL-positive cells were detected in the lamina propria. Conclusions: These results suggest that the activation of the IL-6/STAT-3-signaling pathway plays a pivotal role in the pathogenesis of CD62L+ CD4+ transfer colitis. Moreover, the application of a neutralizing antibody to IL-6R induces apoptosis in transferred T cells. These data implicate the importance of anti-apoptotic pathways in chronic disease and might contribute to future therapies.