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 pron e 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 situa tions was previously investigated only with stimulator lymphocytes and found to be low in intensity and due to an indirect recognition mecha nism involving murine antigen-presenting cells (APC), It was also impo rtant to characterize murine anti-pig islet response. Methods and Resu lts. In the present study, mouse splenocytes responded to pig islet ce lls since primary proliferations were detected in non-diabetes-prone B alb/c (P<0.04) or NOD (P<0.001) mice, Moreover, NOD mice displayed a h igher (P<0.003) splenocyte response to pig islet cells (stimulation in dex: 5.8+/-0.7) than did Balb/c mice (stimulation index: 2.3+/-0.3), w hereas responses to pig stimulator splenocytes were similar in both st rains. The proliferation of NOD splenocytes to pig islet cells was low er (P<0.0001) than the allogeneic response to Balb/c islet cells but s imilar 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 bl ocking of CD, cells had a nonsignificant effect. The main T-splenocyte subsets involved were restricted to mouse MHC class II molecules as t hey did not proliferate in the presence of monoclonal antibodies direc ted at I-A molecules, NOD and Balb/c splenocyte proliferation to pig i slet 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 respond ing to pig islet cells. Both Th1 and Th2 splenocytes were involved in response to pig islet cells since interferon-gamma (IFN-gamma) and int erleukin (IL-)-4 production increased significantly (300-fold and 11-f old, respectively, P<0.02 for both), whereas the increase in IL-10 pro duction was much lower (only 1.5-fold). The IFN-gamma/IL-4 and IFN-gam ma/IL-10 ratios stimulated by pig islet cells were not different with NOD and Balb/c splenocytes. Conclusion. In conclusion mouse cell-media ted reaction against xenogeneic adult pig islet cells mainly involves class LI-restricted CD4+ T lymphocytes of Th1 and Th2 subtypes, with a n indirect pathway for the recognition. Although of low intensity, thi s cell-mediated reaction constitutes an obstacle to pig islet engraftm ent in the mouse, although one not necessarily more insurmountable tha n alloreactivity. The peculiarity of NOD mouse splenocytes, in terms o f proliferation against pig islets, suggests that the study of islet x enograft rejection should take the immunogenetic context of diabetes i nto account, in which case the use of non-diabetes-prone mice has its limitations.