ANTI-CD8 MONOCLONAL ANTIBODY-MEDIATED INHIBITION OF INTESTINAL ALLOGRAFT REJECTION IS ASSOCIATED WITH DOWN-REGULATION OF TH1-TYPE CYTOKINES

Abstract

243 We have previously shown inhibition of intestinal allograft rejection in mice treated with YTS169.4, a depleting anti-CD8 monoclonal antibody (mAb). In the current study, cytokine gene expression in YTS-treated recipients was compared to that of untreated recipients to determine the role of mAb-induced immune deviation in the inhibition of allograft rejection. Methods. Intestinal grafts from B6C3F1/J (H2bxk) or C57BL/6J (H2b) donors were transplanted into C57BL6/J recipients. A group of allograft recipients was treated with a single, pretransplant dose of YTS169.4. Mice were sacrificed on day 14. Adjacent segments of the graft were assessed histologically for rejection (scored 0 - 3; no to severe rejection) and for cytokine production by semiquantitative RT-PCR. Cytokine gene expression was normalized using expression of the housekeeping gene GAPDH. Results. No syngeneic grafts developed rejection (rejection scores (RSs) 0, 0, and 0) while all untreated allograft recipients developed rejection (RSs 3, 1, and 3). Allografts from YTS-treated recipients displayed no or mild rejection (RSs 0, 1, and 1). IFNγ, TNFα, and IL-2 were increased in allografts from untreated recipients when compared to syngeneic grafts (Figure 1). Allografts from YTS-treated recipients expressed less IFNγ and TNFα than did allografts from untreated recipients. IL-12p40 expression was detected only in allografts from untreated recipients. In contrast to the decreased expression of TH1 cytokines, TH2 cytokine expression was unchanged or increased in YTS-treated mice relative to grafts from syngeneic or untreated, allogeneic recipients (Figure 2). Conclusions. Inhibition of intestinal allograft rejection by this anti-CD8 mAb was associated with a decreased expression of the TH1 cytokines IFNγ, IL-12, and TNFα and an unchanged or slightly augmented expression of TH2 cytokines. We have previously shown that YTS169.4 inhibited rejection of intestinal allografts in mice deficient in TH2-type responses (IL4 and STAT6 knockout mice). Together, these data suggest that the YTS-induced inhibition of intestinal allograft rejection may be more dependent upon the down-regulation of TH1 cytokines than upon the augmentation of TH2 cytokine production.FIGURE 1FIGURE 2