Phenotypic and functional characteristics of intestinal intraepithelial lymphocytes during acute rejection of small intestinal allografts

Immune cell profiling in intestinal transplantation

Since the first published case study of human intestinal transplantation in 1967, there have been significant studies of intestinal transplant immunology in both animal models and humans. An improved understanding of the profiles of different immune cell subsets is critical for understanding their contributions to graft outcomes. While different studies have focused on the contribution of one or a few subsets to intestinal transplant, no study has integrated these data for a comprehensive overview of immune dynamics after intestinal transplant. Here, we provide a systematic review of the literature on different immune subsets and discuss their roles in intestinal transplant outcomes on multiple levels, focusing on chimerism and graft immune reconstitution, clonal alloreactivity, and cell phenotype. In Sections 1, 2 and 3, we lay out a shared framework for understanding intestinal transplant, focusing on the mechanisms of rejection or tolerance in the context of mucosal immunology and illustrate the unique role of the bidirectional graft-versus-host (GvH) and host-versus-graft (HvG) alloresponse. In Sections 4, 5 and 6, we further expand upon these concepts as we discuss the contribution of different cell subsets to intestinal transplant. An improved understanding of intestinal transplantation immunology will bring us closer to maximizing the potential of this important treatment.

Attenuation of rat chronic small bowel allograft rejection by n-3 polyunsaturated fatty acids is associated with reduced expression of graft IL-15

Interleukin-15 was found to play key roles in various immunological processes including chronic rejection after renal and cardiac transplantation. n-3 polyunsaturated fatty acids (n-3 PUFA) have shown beneficial effects to chronic allograft rejection. The objective of this study is to search the possible mechanism of this inhibitory effect in chronic small bowel allograft rejection. Animals were divided into three groups: isograft (CsA + corn oil-supplemented diet); allograft (CsA + corn oil-supplemented diet); and allograft (CsA + fish oil-supplemented diet). Donor intestines from F344 rats were transplanted orthotopically into Lewis rat recipients. CsA was administered at 5 mg/kg/day for 2 wk post-operatively. Post-transplant weight was recorded. Histopathological changes and graft IL-15 expression were measured on POD 90. Chronic small bowel allograft rejection developed on POD 90. n-3 PUFA significantly decreased the score of chronic rejection and increased the post-operative weight gain rate. This attenuation is associated with reduced graft IL-15 expression. n-3 PUFA contributed to improved pathological and clinical outcome during chronic small bowel allograft rejection, and this improvement was associated with reduced graft IL-15 expression.

Impact of antimouse CD52 monoclonal antibody on graft's γδ intraepithelial lymphocytes after orthotopic small bowel transplantation in mice

Alemtuzumab, a humanized CD52 monoclonal antibody (mAb), has been used for immune induction in clinical small bowel transplantation (SBT). However, the local impact of CD52 mAb on the transplanted intestine is not known. In this study, we investigated the effects of CD52 mAb on the intestinal intraepithelial lymphocytes (iIELs) in grafts using a murine orthotopic SBT model. The antimouse CD52 mAb was used as a surrogate antibody. Graft rejection was assessed by histopathologic analysis, iIELs were isolated for flow cytometric analysis, the mucosal keratinocyte growth factor (KGF) expression was evaluated by real-time polymerase chain reaction, and epithelial cell (EC) proliferation (percent bromodeoxyuridine incorporation) was measured by immunohistochemistry. No mice showed evidence of rejection. Seven days after SBT, when the CD52 mAb was used, the numbers of iIELs and both T-cell receptor (TCR) γδ and TCRαβ subpopulations were decreased, and the number of TCRγδ iIELs of donor origin was prominently reduced in the allografts. Furthermore, TCRγδ iIEL-derived KGF messenger RNA expression and EC proliferation decreased significantly after CD52 mAb application. These data demonstrate that the antimouse CD52 mAb could deplete iIELs in the transplanted intestine, especially the TCRγδ subset of donor origin. The reduction of TCRγδ iIELs accompanied the decrease in mucosal KGF expression and EC proliferation, which may slow down the epithelial turnover and retard the repair of the damaged epithelium.

Effects of long-term cyclosporine A on rat intestinal intraepithelial lymphocytes

The aim of this study was to assess the influence of long-term administration of cyclosporine (CsA) on rat intestinal intraepithelial lymphocytes (IEL). Ten male Lewis rats were randomly assigned to either a treatment or a control group. For 12 weeks the treatment group received CsA (5 mg/kg per day) while the control group received the same volume of vehicle. Peripheral blood lymphocytes were counted and IEL were isolated for flow cytometric analysis. Peripheral blood lymphocytes numbers were significantly decreased in the CsA compared with the control group (4.80 +/- 1.02 x 10(6)/mL and 3.34 +/- 0.70 x 10(6)/mL, respectively, P = .029). IEL numbers were increased significantly in CsA compared with the control group. (23.2 +/- 8.0 x 10(6) and 7.8 +/- 1.8 x 10(6), respectively, P = .012). There were no significant differences between the two groups considering IEL phenotypes. In conclusion, CsA did not influence the subpopulation but significantly increased the number of IEL.

Intragraft distribution of lymphocytes expressing β7 integrins after small bowel transplantation in mice

Lymphocytes with activated beta7 integrins (alphaEbeta7 and alpha4beta7) contribute to inflammatory reactions in the small bowel. Since the selective recruitment of lymphocytes to the lymphoid compartments of the small bowel is controlled by distinct adhesion molecule interactions, a compartment-dependent use of beta7 integrins may influence the rejection response within intestinal transplants. To further delineate the nature of beta7 integrin-mediated graft infiltration, we analysed their expression on T lymphocytes in the heterotopically transplanted small bowel of BALB/c and C57BL/6 mice. Lymphocytes isolated from the epithelium, lamina propria (LP), Peyer's patches (PP), and mesenteric lymph nodes (MLN) were analysed by three-color fluorescence flow cytometry using monoclonal antibodies (mAb) to integrin the subunits, lymphocyte markers, and MHC I of the donor and recipient strains. On postoperative day 5 (POD) after allogeneic small bowel transplantation (SBT), 43% of intraepithelial lymphocytes (IEL) and 63% of LP, 93% of MLN, and 93% of PP lymphocytes were of host origin. In the MLN and PP of allografts, a major infiltrating lymphocyte population consisted of CD8+ cells with increased expression of alpha4beta7 and decreased expression of L-selectin, an adhesion molecule profile characteristic of intestinal effector cell phenotypes. An increase in alpha4beta7 levels was also found on CD8+ host lymphocytes in the LP. The integrin profile of a number of host IEL suggests an ongoing transition from the phenotype of graft infiltrating lymphocytes with high levels of alpha4beta7 and low levels of alphaepsilonbeta7 to that of resident IEL with high levels of alphaepsilonbeta7 and low levels of alpha4beta7. The importance of beta7-mediated lymphocyte trafficking to the graft is attested by the significant reduction in the host lymphocyte population in the LP, PP, and epithelium following the administration of a beta7-blocking mAb to allograft recipients. In conclusion, while the infiltration patterns of lymphocytes may vary between the lymphoid compartments of intestinal allografts, host CD8+ lymphocytes with high levels of alpha4beta7 constitute a major effector cell population that affects the entire graft.

FTY720 reduces T-cell recruitment into murine intestinal allograft and prevents activation of graft-infiltrating cells

BACKGROUND

Effective immunosuppression is a critical determinant of graft survival in small-bowel transplantation (SBTx). The present study was designed to determine the potency of FTY720, a newly synthesized immunosuppressant, in rat SBTx and examine the phenotype of graft-infiltrating cells to evaluate its effect on intestinal allografts.

MATERIALS AND METHODS

A segment of intestine of Dark Agouti rats was transplanted heterotopically into Lewis rats. The recipients were treated with or without oral FTY720 at a dose of 1 mg/kg per day. Six days after surgery, peripheral blood lymphocytes and lymphocytes from the mesenteric lymph nodes, Peyer's patches, intraepithelial site, and lamina propria of the intestinal allograft were isolated. After the number of lymphocytes in each site was counted, the lymphocyte subpopulations in the intestinal allograft were evaluated by means of a FACScan flow cytometer using several monoclonal antibodies.

RESULTS

FTY720 treatment significantly prolonged recipient survival and strongly inhibited rejection histologically in comparison with control rats. FTY720 immunosuppression resulted in a marked reduction of lymphocyte number in the graft epithelium and lamina propria and the proportion of CD8+ and CD25+ cells. FTY720 also significantly decreased T-cell receptors and increased B cells in the graft Peyer's patches.

CONCLUSION

FTY720 promoted long-term SBTx recipient survival and maintained the architecture of intestinal allografts. FTY720 immunosuppression may be associated with a reduction of T-cell recruitment subsequent to the redistribution of lymphocyte subpopulations to control the proliferation and activation of graft-infiltrating cells in intestinal allografts.

Monoclonal antibody against beta7 integrins, but not beta7 deficiency, attenuates intestinal allograft rejection in mice

BACKGROUND

beta7 integrins mediate homing and retention of lymphocytes to the normal and inflamed small bowel in a tissue-selective fashion. In the present study, we investigated the expression of beta7 integrins after small bowel transplantation (SBT) and tested the effects of blocking beta7-mediated pathways by using monoclonal antibody (mAb) or knockout mice.

METHODS

Heterotopic SBT from BALB/c to C57BL/6 (B6) was used as a surgical model. Expression of beta7 integrins was measured on recipient lymphocytes (CD4 and CD8 ) in spleen, blood, and mesenteric lymph nodes (MLN) using flow cytometry. To analyze the effects of blocking beta7 integrins on graft survival, either beta7-deficient B6 or wild-type B6 mice that were treated with mAb against beta7 were studied.

RESULTS

After allogeneic SBT, there were markedly increased levels of alpha4beta7 recipient CD8 lymphocytes in MLN, blood, and spleen as early as 3 days postoperatively. In contrast, alpha4beta7 integrin levels in isograft recipients were similar to those of normal mice. Mean survival time of intestinal allografts was not affected by beta7 deficiency (7.3+/-1 days) compared with wild-type mice (7.5+/-0.8 days). However, mAb against beta7 integrins significantly prolonged graft survival (12.8+/-1 days) compared with treatment with control mAb (7.3+/-1 days, <0.001). Histologic changes of SBT rejection were significantly attenuated when mice were given mAb against beta7.

CONCLUSION

As indicated by the increased levels of alpha4beta7 CD8 lymphocytes, activation of this integrin contributes to the immune response in SBT rejection. Furthermore, blocking beta7 integrins with mAb provides a suitable target for immunosuppressive therapy. The discrepancy in survival data obtained by mAb and beta7 deficiency may be a result of the more rapid activation of compensatory mechanisms in the knockout mice.