In vitro xenorecognition of adult pig pancreatic islet cells by splenocytes from nonobese diabetic or non-diabetes-prone mice.

BACKGROUND

In vitro studies of the nonobese diabetic (NOD) mouse prone to type 1 autoimmune diabetes were conducted in order to investigate the mechanisms possibly involved in cell-mediated rejection of adult pig islet xenografts. Mouse cellular proliferation in discordant situations was previously investigated only with stimulator lymphocytes and found to be low in intensity and due to an indirect recognition mechanism involving murine antigen-presenting cells (APC). It was also important to characterize murine anti-pig islet response.

METHODS AND RESULTS

In the present study, mouse splenocytes responded to pig islet cells since primary proliferations were detected in non-diabetes-prone Balb/c (P<0.04) or NOD (P<0.001) mice. Moreover, NOD mice displayed a higher (P<0.003) splenocyte response to pig islet cells (stimulation index: 5.8+/-0.7) than did Balb/c mice (stimulation index: 2.3+/-0.3), whereas responses to pig stimulator splenocytes were similar in both strains. The proliferation of NOD splenocytes to pig islet cells was lower (P<0.0001) than the allogeneic response to Balb/c islet cells but similar to syngeneic proliferation to NOD islet cells. In both NOD and Balb/c mice, splenocyte proliferation to pig islet cells was abolished (P<0.01) when CD4+ cells were blocked with antibodies, whereas the blocking of CD8+ cells had a nonsignificant effect. The main T-splenocyte subsets involved were restricted to mouse MHC class II molecules as they did not proliferate in the presence of monoclonal antibodies directed at I-A molecules. NOD and Balb/c splenocyte proliferation to pig islet cells was abolished after removal of plastic-adherent APC, which indicates that the major activation pathway was indirect. Purified CD4+ or CD8- cells alone did not proliferate in response to pig islet cells but recovered a proliferative ability when mixed with APC. CD4- cells, alone or in the presence of APC, were not capable of responding to pig islet cells. Both Th1 and Th2 splenocytes were involved in response to pig islet cells since interferon-gamma (IFN-gamma) and interleukin (IL-)-4 production increased significantly (300-fold and 11-fold, respectively, P<0.02 for both), whereas the increase in IL-10 production was much lower (only 1.5-fold). The IFN-gamma/IL-4 and IFN-gamma/IL-10 ratios stimulated by pig islet cells were not different with NOD and Balb/c splenocytes.

CONCLUSION

In conclusion, mouse cell-mediated reaction against xenogeneic adult pig islet cells mainly involves class II-restricted CD4+ T lymphocytes of Th1 and Th2 subtypes, with an indirect pathway for the recognition. Although of low intensity, this cell-mediated reaction constitutes an obstacle to pig islet engraftment in the mouse, although one not necessarily more insurmountable than alloreactivity. The peculiarity of NOD mouse splenocytes, in terms of proliferation against pig islets, suggests that the study of islet xenograft rejection should take the immunogenetic context of diabetes into account, in which case the use of non-diabetes-prone mice has its limitations.