The replacement of graft endothelium by recipient-type cells conditions allograft rejection mediated by indirect pathway CD4(+) T cells

BACKGROUND: Whereas the participation of alloreactive T cells sensitized by indirect allorecognition in graft rejection is well documented, the nature of recipient antigen presenting cells recognized by indirect pathway CD4(+) T cells within the graft has yet to be identified. The purpose of this study was to determine the role played by graft endothelium replacement in the immune recognition of cardiac allografts rejected by indirect pathway CD4(+) T cells. METHODS: Transgenic RAG2(-/-) mice expressing I-A(b)-restricted male antigen H-Y-specific TcR were studied for their capacity to reject H-2(k) male cardiac allografts. Chronic vascular rejection in this model was due to the indirect recognition of H-Y antigen shed from H-2(k) male allograft and presented by the recipient's own I-A(b) APC to transgenic T cells. RESULTS: Immunohistochemical analysis of rejected grafts revealed the presence of numerous microvascular endothelial cells (EC) that expressed recipient's I-A MHC class II molecules. This observation suggested that graft endothelium replacement by I-A(b)-positive cells of recipient origin could stimulate the rejection of male H-2(k) graft by I-A(b)--restricted H-Y--specific T cells. To investigate further this possibility, hearts from H-2(b)--into--H-2(k) irradiation bone marrow (BM) chimera were transplanted in transgenic recipients. A direct correlation was observed between the presence of I-A(b)-positive EC within myocardial microvessels and the induction of acute rejection of chimeric H-2(k) male cardiac allografts transplanted in transgenic recipients. CONCLUSIONS: We conclude that graft endothelium replacement by recipient-type cells is required for the rejection of cardiac allograft mediated by indirect pathway alloreactive CD4(+) T cells.     

CD4+ T cells responsive through the indirect pathway can mediate skin graft rejection in the absence of interferon-gamma

BACKGROUND: T cells responding through the indirect pathway can induce allograft rejection, but mechanisms of rejection are not known. Interferon-y (IFN-gamma) may be an important mediator of rejection under these circumstances. METHODS: We transferred CD4+ T cells from IFN-gamma-deficient (IFN-gamma-/-) mice into SCID recipients of MHC II-deficient (MHC II-/-) skin grafts. Under these conditions, rejection can only occur via the indirect pathway and cannot be mediated by T-cell production of IFN-gamma. RESULTS: IFN-gamma-/- CD4+ T cells rejected MHC II -/- skin grafts. Flow cytometry revealed only CD4+ T cells in the recipients. Cytokine enzyme-linked immunosorbent spot assays confirmed only indirect recognition with an associated expansion of an alloreactive population of IL-2-, IL-4-, and IL-5-secreting T cells. CONCLUSION: CD4+ T cells recognizing alloantigens via the indirect pathway can mediate skin graft rejection in the absence of IFN-gamma.     

Mediation of skin allograft rejection in scid mice by CD4+ and CD8+ T cells.

We analyzed the role of CD4+ and CD8+ T cells in H-2-disparate skin allograft rejection in the mutant mouse strain C.B-17/Icr scid with severe combined immunodeficiency. On the day of skin allografting, scid mice were adoptively transferred with negatively selected CD4+ or CD8+ splenocytes from normal unsensitized C.B-17/Icr mice. These populations were obtained using a double-mAb--plus--complement elimination protocol using anti-CD4 or anti-CD8 mAb that resulted in no detectable CD4+ or CD8+ cells by FACS and negligible numbers of cytolytic T lymphocytes by limiting dilution analysis in anti-CD8 treated populations. Spleen cells were removed from grafted mice at the time of rejection and were tested in vitro for antidonor reactivity in several assays: mixed lymphocyte culture, cell-mediated lympholysis, and LDA for CTL and for IL-2-producing HTL. The presence of Thy 1.2+, CD4+, or CD8+ cells was determined by FACS. All control C.B-17 mice and scid mice adoptively transferred with nondepleted CD4+, and CD8+ cells rejected skin allografts with similar mean survival times (15.6 +/- 1.5, 18.8 +/- 3.4, 18.0 +/- 5.4, respectively), whereas control scid mice retain skin allografts indefinitely (all greater than 100 days). C.B-17 syngeneic grafts survived indefinitely in all groups. At the time of rejection, splenocytes from scid mice receiving CD4+ cells had negligible donor-specific cytotoxicity in CML and negligible numbers of CTL by LDA, but demonstrated a good proliferative response in MLC and IL-2-producing cells by LDA (frequency = 1/1764). There were no detectable CD8+ cells present by FACS analysis. Conversely, splenocytes from scid mice adoptively transferred with CD8+ cells had strong donor-specific cytotoxicity in CML (58.8% +/- 16.1%) and CTL by LDA (frequency = 1/3448), but no significant proliferation was detected in MLC. There were no detectable CD4+ cells by FACS, but there were small numbers of IL-2-producing cells by LDA (frequency = 1/10,204). These data demonstrate that CD4+ cells adoptively transferred into scid mice are capable of mediating skin allograft rejection in the absence of any detectable CD8+ cells or significant functional cytolytic activity. The adoptive transfer of CD8+ cells also results in skin allograft rejection in the absence of detectable CD4+ cells. The detection of small numbers of IL-2 secreting cells in these mice may indicate that CD(8+)-mediated allograft rejection in this model is dependent on IL-2-secreting CD8+ cells.     

Rejection of porcine islet xenografts mediated by CD4+ T cells activated through the indirect antigen recognition pathway

We have previously demonstrated that human T cells responding to porcine islets are primarily CD4+ and recognized porcine major histocompatibility complex class I molecules through the indirect pathway of antigen presentation. To determine whether this mechanism is responsible for rejection of adult porcine islets xenografts, porcine islets from adult pigs were transplanted under the kidney capsule of streptozotocin-treated CD4-knockout (KO), CD8-KO, Ig-KO and normal C57BL/6 mice. Islet xenografts were acutely rejected with similar kinetics when transplanted into normal C57BL/6 (MST=17.6 +/- 3.5 days) and Ig-KO (MST=19.0 +/- 1.7 days) mice. Interestingly, islet xenografts were rejected significantly earlier when transplanted into CD8-KO mice as compared with normal C57BL/6 (MST=7.0 +/- 0.01 days, P=2 x 10-4). Histopathological analysis revealed classical acute cellular rejection with severe diffuse interstitial cellular infiltrates in all rejected islet xenografts. In contrast, islet xenografts were not rejected when transplanted into CD4-KO mice (MST >/= 100 days, P=1 x 10-9). Histopathological analysis revealed no cellular infiltrates and intact islet xenografts. CD4+ T cells from both normal C57BL/6 and CD8-KO xenograft recipients showed detectable proliferative responses to porcine islets in the presence but not in the absence of syngeneic antigen-presenting cells. In addition, the anti-islet proliferative responses observed in normal C57BL/6 mice were significantly lower than those observed in CD8-KO mice. IgG anti-porcine antibodies were readily detected in C57BL/6 and CD8-KO xenograft recipients but not in Ig-KO or CD4-KO recipients. These results indicate that indirectly activated CD4+ T cells mediate acute rejection of adult porcine islet xenografts and that xenoreactive CD8+ T cells and antibodies are not necessary in this process.     

Targeting acute allograft rejection by immunotherapy with ex vivo-expanded natural CD4+ CD25+ regulatory T cells

BACKGROUND: Natural CD4CD25 regulatory T (Treg) cells have been implicated in suppressing alloreactivity in vitro and in vivo. We hypothesized that immunotherapy using ex vivo-expanded natural Treg could prevent acute allograft rejection in mice. METHODS: Natural CD4+ CD25+ Treg were freshly purified from naive mice via automated magnetic cell sorter and expanded ex vivo by anti-CD3/CD28 monoclonal antibody (mAb)-coated Dynabeads. Suppression was assayed in vitro by mixed lymphocyte reaction and in vivo by targeting cardiac allograft rejection. Survival of Treg or effector T (Teff) cells after adoptive transfer in vivo was tracked by flow cytometry and all allografts were examined by histology and immunohistochemistry. RESULTS: By day nine in culture, 26.6+/-5.3-fold of expansion was achieved by co-culture of fresh natural Treg with anti-CD3/CD28 mAb-coated Dynabeads and interleukin-2. Ex vivo-expanded Treg exerted stronger suppression than fresh ones towards alloantigens in vitro and prevented CD4 Teff-mediated but only delayed CD4+/CD8+ Teff-mediated heart allograft rejection in Rag-/- mice. Long-term surviving allografts showed no signs of acute or chronic rejection with graft-infiltrating Treg expressing CD25 and FoxP3. Infused Treg persisted and expanded long-term in vivo and trafficked through the peripheral lymphoid tissues. CD25 expression was dynamic in vivo: maintained CD25 expression on Treg was indicative for the preservation of allosuppression, while significantly enhanced CD25 expression on CD4+ effector T cells was most likely associated with T-cell expansion and graft rejection. CONCLUSIONS: Therapeutic use of ex vivo-expanded natural CD4+ CD25+ Treg may be a feasible and nontoxic modality for controlling allograft rejection or perhaps inducing allograft tolerance.     

The role of CD8+ and CD4+ cells in islet allograft rejection

The requirements of CD8+ and CD4+ cells for islet graft rejection in combinations with different histoincompatibilities were investigated by in vivo administration of anti-Lyt-2.2 (CD8) mAb, anti-L3T4 (CD4) mAb, or both to recipient mice. In B10.AQR----B10.A (H-2K-incompatible) and B10.A(5R)----B10.A (H-2K- and IA-incompatible) combinations, administration of either anti-Lyt-2.2 (CD8) or anti-L3T4 (CD4) mAb completely blocked islet graft rejection, indicating that neither CD8+ cells nor CD4+ cells alone were capable of mediating rejection, and that collaboration of CD8+ cells and CD4+ cells was necessary. On the other hand, in the BALB/c----B6 (H-2- and non-H-2-incompatible) combination, administration of anti-Lyt-2.2 (CD8) or anti-L3T4 (CD4) mAb resulted in rejection of most of the grafts, although survival was prolonged significantly, and administration of both anti-Lyt-2.2 (CD8) and anti-L3T4 (CD4) mAb together completely blocked rejection. These results suggested that either CD8+ or CD4+ cells were capable of mediating rejection, but that rejection was maximal in the presence of both T cell subsets. Immunohistochemical analyses showed marked depletion of CD8+ cells and CD4+ cells in grafted islets as well as spleens when anti-Lyt-2.2 (CD8) and anti-L3T4 (CD4) mAb, respectively, were injected.     

Renal allograft rejection in CD4+ T cell-reconstituted athymic nude rats. The origin of CD4+ and CD8+ graft-infiltrating cells

PVG-rnu/rnu nude rats reject a fully allogeneic DA renal allograft after the adoptive transfer of naive CD4+ T cells alone, but rejection is accompanied by the accumulation of many CD8+ leukocytes within the graft. In order to clearly establish the provenance of these CD8+ cells infiltrating rejecting kidney allografts, nude recipients (PVG-RT7a) were injected with CD4+ T cells from the PVG-RT7b congenic strain bearing an allotypic variant of the leukocyte-common antigen. Dual fluorescence and immunohistochemistry demonstrated that approximately 75% of the total infiltrate was host-derived; the donor-derived RT7b population was almost entirely (92-99%) CD4+, CD5+, CD3+, and alpha beta TCR+. At least 97% of the CD8+ cells were of nude origin. There was no evidence of donor-derived CD8+ cells or of a CD4+8+ double-staining population. Unexpectedly, nearly half of the alpha beta TCR+ cells from the grafts were of nude origin.     

The expansion of CD4+CD28- T cells in patients with chronic kidney graft rejection

CD4+CD28- T cells are oligoclonal lymphocytes rarely found in healthy subjects, but are present in high frequencies in patients with inflammatory diseases. Contrary to paradigm, they are functionally active and produce interferon gamma and cytolytic proteins, are cytotoxic in vessels and may contribute to tissue damage. The size of the peripheral blood CD4+CD28- T cell compartments was determined in 20 healthy individuals, 20 patients after renal transplantation with stable graft function, and 20 with chronic graft rejection by two-color FACS analysis. In patients with stable graft function, the median frequency of CD4+CD28- T cells was 3.1% and was significantly higher in comparison to the control group (1.4%) (P <.01).The highest subset CD4+CD28- cells was detected in patients with chronic graft rejection (10.65%). The amount of CD4+CD28- cells was significantly higher in this group in comparison to patients with stable graft function (P <.01). The evaluated number of CD4+CD28- cells in patients after renal transplantation, especially in graft recipients with chronic graft rejection, suggests a role of these cells in chronic graft destruction.     

Rapamycin or tacrolimus alone fails to resist cardiac allograft accelerated rejection mediated by alloreactive CD4+ memory T cells in mice

Donor-reactive memory T (Tm) cells undermine transplanted organs more readily than naive T cells. Rapamycin (RAPA) and tacrolimus (FK-506) are current mainstay immunosuppressants used for preventing acute allograft rejection. Although their efficacy in suppressing naive T cell is established, their suppressing effect on memory T cells is undefined. This study was conducted to investigate the inhibiting capability of RAPA or FK-506 against transferred alloreactive CD4⁺ Tm cells in a mouse cardiac transplant model. We found that these drugs alone prolonged the median survival time (MST) of allograft from 5 days to 9 days in recipient mice with CD4⁺ Tm infusion (P < 0.01), which however was not significantly longer than that (8 days) in untreated recipient mice without CD4⁺ Tm infusion (naive control). Mean histologic rank of rejection activity in section of cardiac allograft on day 5 postgrafting was Grade 4 in the Tm control recipients versus Grade 3A in both of the immunosuppressant treatment recipients with CD4⁺ Tm infusion. RAPA or FK-506 alone failed to completely suppress proliferation and differentiation of the alloreactive CD4⁺ Tm, which was confirmed by in vitro mixed lymphocyte reaction (MLR) and by flow cytometry (FCM) of the splenocytes for detecting CD44^highCD62L⁻ effector/memory as well as CD69⁺/CD25⁺ activation phenotype cells from the respective recipients. Furthermore, the agent alone didn't completely inhibit the activation of CD4⁺ Tm, for serum level of IFN-γ and its gene expression at the cardiac allograft from the immunosuppressant-treated recipients were as still high as the untreated naive control. Thus, RAPA or FK-506 alone couldn't completely suppress the proliferation and activation of the alloantigen-primed CD4⁺ Tm cells responding to the alloantigen, indicating that alloreactive CD4⁺ Tm was insensitive to these immunosuppressants. The characteristics of alloreactive CD4⁺ Tm to resist immunosuppressants and its potency to initiate quick and vigorous rejection despite treatment with the immunosuppressant make it to be a critical barrier to prolongation of allograft survival and induction of transplant tolerance.     

Blockade of indirect recognition mediated by CD4+ T cells leads to prolonged cardiac xenograft survival

Abstract:  The T-cell response to xenografts is induced by direct and indirect recognition of xenoantigens. Although the importance of indirect recognition is well established in vitro, the contribution of this pathway to xenograft rejection in vivo remains to be fully elucidated. We herein investigated the direct contribution of indirect recognition to cardiac xenograft rejection in the rat-to-mouse (PVG.R8-to-C57BL/10) concordant model. Rat xenoantigens invoked a vigorous proliferative response in mouse T cells harvested from naïve or graft recipients at rejection. Indirect recognition predominated the response, as antibodies against mouse class II I-A^b, CD80, or CD86 molecules significantly (45 to 60%) blocked the proliferative response. Importantly, the blockade of indirect recognition in vivo by treating the graft recipients with a monoclonal antibody (mAb) against class II I-A^b molecule on days 0, 1, and 3 post-transplantation resulted in significant ( P  < 0.009) prolongation of cardiac xenograft survival (Mean Survival Time (MST) >94 ± 55 days vs. 7 ± 0.8 days for controls). In contrast, treatment of recipients with a mAb against mouse class I H-2K^b/D^b molecules did not significantly affect graft rejection (MST = 8 ± 1 days). These results demonstrate that indirect recognition mediated by CD4⁺ T cells plays a critical role in the rejection of cardiac grafts in the rat-to-mouse xenogeneic model.     

CD4+ CD25+ regulatory T cells suppressed the indirect xenogeneic immune response mediated by porcine epithelial cell pulsed dendritic cells

Nishimura T, Onda M, Takao S. CD4⁺ CD25⁺ regulatory T cells suppressed the indirect xenogeneic immune response mediated by porcine epithelial cell pulsed dendritic cells. Xenotransplantation 2010; 17: 313–323. © 2010 John Wiley & Sons A/S. Abstract: Background: CD4⁺ CD25⁺ regulatory T cells have been reported to suppress T cell‐mediated xenogeneic immune responses. Although the direct T cell response to xenogeneic cells is important, the indirect xenogeneic immune response mediated by dendritic cells (DCs) is also likely involved in rejection. We have generated an in vitro indirect immune reaction model and evaluated the effect of CD4⁺ CD25⁺ regulatory T cells on this system. Methods: Human DCs were generated from peripheral blood and cultured with X‐ray‐irradiated porcine kidney epithelial cells. Porcine cell‐pulsed DCs were mixed with autologous CD4⁺ T cells, CD4⁺ CD25^? T cells and/or CD4⁺ CD25⁺ T cells. After 7 days of culture, T cell proliferation was measured. Results: The co‐culture of human DCs and X‐ray‐irradiated porcine epithelial cells resulted in observable DC phagocytic activity within 2 days. These porcine cell–pulsed DCs stimulated CD4⁺ T cell proliferation much more potently than unpulsed DCs or porcine cells. This proliferation was blocked by CTLA4‐Ig or an anti‐HLA‐DR antibody. CD4⁺ CD25⁺ regulatory T cells also suppressed CD4⁺ CD25^? T cell proliferation in response to porcine cell‐pulsed DCs. Conclusions: An in vitro model of the indirect xenogeneic immune response was established. Porcine cell‐pulsed DCs stimulated CD4⁺ T cells, and CD4⁺ CD25⁺ regulatory T cells suppressed this response.     

肝移植急性排斥反应者外周血CD4+CD25+Foxp3+调节性T淋巴细胞的变化

目的 探讨良性终末期肝病患者肝移植术后外周血CD4+CD25+叉状头螺旋转录因子(Foxp3)+调节性T淋巴细胞在急性排斥反应期的变化及意义.方法 2004年12月至2008年1月间,符合入选条件的良性终末期肝病患者共55例,按照术后是否发生急性排斥反应分为排斥组(14例)和无排斥组(41例).肝移植术前用流式细胞仪检测患者外周血CD4+CD25+Foxp3+T淋巴细胞占CD4+T淋巴细胞的百分率(简称CD4+CD25+Foxp3+T细胞百分率),出院后1年内每隔3～6个月复查;发生急性排斥反应时,于治疗前和治疗缓解后(3～6个月)复查.比较两组患者外周血CD4+CD25+Foxp3+T细胞百分率的变化,对排斥组发生急性排斥反应时外周血CD4+CD25+Foxr3+T细胞百分率与排斥反应活动指数(RAI的相关性进行统计学分析.结果 肝移植术前,排斥组与无排斥组外周血CD4+CD25+Foxp3+T细胞百分率的差异无统计学意义(P＞0.05).排斥组患者发生急性排斥反应时外周血CD4+CD25+Foxp3+T细胞百分率为(2.23±0.54)%,低于无排斥组的(2.99±0.86)%,差异有统计学意义(P＜0.01).排斥组中,患者发生急性排斥反应时外周血CD4+CD25+Foxp3+T细胞百分率低于未发生急性排斥反应时的(3.67±0.70)%,差异有统计学意义(P＜0.01).排斥组患者发生急性排斥反应时外周血CD4+CD25+Foxp3+T细胞百分率与RAI呈负相关(r=-0.80,P＜0.01).结论 监测肝移植受者外周血CD4+CD25+Foxp3+调节性T淋巴细胞的变化,可辅助诊断急性排斥反应及判断其严重程度.

Abstract：

Objective To investigate the expression of peripheral blood (PB) CD4+ CD25+ Foxp3+ regulatory T cells (Tregs) in patients with benign end-stage liver disease after liver transplantation and the relationship between levels of PB Tregs and acute rejection. Methods A prospective analysis was performed on 55 consecutive patients who underwent liver transplantation.Fourteen out of 55 cases suffered from acute rejection after liver transplantation were defined as rejection group,while the rest patients were classified into no acute rejection group. PB was obtained from liver transplant patients at different time points longitudinally: pre-transplant, post-transplant within one year and acute rejection. The circulating CD4+ CD25+ Foxp3+ Tregs in PB were measured by flow cytometry. Blood samples were drawn during acute rejection, at the same time, liver biopsies were performed. The circulating CD4+ CD25+ Foxp3+ Tregs were compared between two groups.Results There was no difference between two groups in levels of circulating CD4+ CD25+ Foxp3 + Tregs cells pre-transplant. However, the levels of circulating CD4+ CD25+ Foxp3+ Tregs in rejection group were decreased significantly as compared with no-rejection group (2. 23 % ± 0. 54 % vs. 2. 99 % ±0. 86 %,P＜0.01). The frequency of CD4+ CD25+ Foxp3+ T cells was negatively correlated with rejection activity index (RAI) (r = - 0. 80, P＜0. 01 ). Conclusion Monitoring PB CD4+ CD25+ Foxp3+ Tregs levels may be helpful in evaluating the immune state and act as a more sensitive marker for acute rejection diagnosis in the patients following liver transplantation.     

Role of CD4+ and CD8+ T cells in early and late acute rejection of small bowel allograft

BACKGROUND/PURPOSE: Results of small bowel transplantation remain unsatisfactory because of severe immune rejection. The current study aims to elucidate the role of activation of CD4+ and CD8+ T cells in early and late acute rejection of small bowel allograft and, hence, provide the immunologic basis for developing new therapeutic strategies. METHODS: We used an MHC fully mismatched (DA to Lewis) heterotopic rat small bowel transplant model and a unique FK506-based immunosuppressive regimen, which suppresses early acute rejection but does not prevent late acute rejection. Flow cytometric analysis was used to quantitate the number of activated CD4+ and CD8+ T cells in graft and host mesenteric lymph nodes. RESULTS: The survival (mean +/- SD) of intestinal allograft was significantly prolonged, from 6.6 +/- 0.84 days for the untreated group to 40.7 +/- 14.1 days for the FK506-treated group. Activation of CD4+ cells was suppressed significantly in the FK506-treated group on postoperative day 7 compared with the untreated group (29.4% +/- 3.55% v 52.83% +/- 11.9%; P <.01). Activation of CD8+ cells was similarly suppressed (31.5 +/- 10.34% v 48.53 +/- 14.34%; P <.05). Interestingly, at late acute rejection, activated CD4+ and CD8+ T cells remained at almost the same low levels as those on postoperative day 7 in the FK506-treated group. The spleen to body weight ratio was significantly increased in the untreated group (0.53 +/- 0.07), and slightly increased in the FK treated group (0.27 +/- 0.07, on postoperative day 7; 0.24 +/- 0.07 at late acute rejection) compared with the syngeneic group (0.18 +/- 0.02). CONCLUSION: The activation of CD4+ and CD8+ T cells was suppressed effectively by early potent immunosuppressive treatment resulting in prolonged survival of intestinal allograft. At late acute rejection, the CD4+ and CD8+ T cells remained at low-level activation status, in contrast to the surge of CD4+ and CD8+ activation during early acute rejection. This suggests that persistent T cell activation even at low level is sufficient to cause the late acute rejection eventually. A therapeutic strategy targeting these cells is needed for long-term engraftment.     

CD4+ T cells are critical for corneal, but not skin, allograft rejection

BACKGROUND: The relative contribution of CD4+ or CD8+ T cells in allograft rejection remains to be fully characterized. Some reports indicate that there is an absolute requirement for CD4+ T cells in allogeneic rejection, whereas others report that CD4-depleted mice are capable of rejecting certain types of allografts. METHODS: We compared the ability of CD4- knockout (KO), CD8- KO, and normal CD4+/CD8+ mice to reject allogeneic corneal or skin grafts. We also examined delayed-type hypersensitivity and CTL responses to donor alloantigens. RESULTS: Engraftment of C57BL/6 corneas to C.B6-(n5-7) CD4-KO mice resulted in significantly higher rates of acceptance (>85%) than either C.B6-(n5-7) CD8- KO (30%) or normal BALB/c mice (40%). Likewise, mean survival times for B6 skin grafts placed on C.B6-(n5-7) CD4- KO mice (29.2 +/- 3.5 days) were significantly increased over those of normal BALB/c mice (13.2 +/- 1 days), although most CD4- KO mice (70%) eventually reject their grafts. C.B6-(n5-7) CD4- KO mice that reject allogeneic grafts fail to develop a delayed-type hypersensitivity response, but they did demonstrate significantly greater cytotoxic T lymphocyte precursor (CTLp) frequencies than did CD4- KO mice that accepted such grafts or that were not grafted. CONCLUSIONS: This study indicates that mice lacking CD4+ T cells have a significantly impaired ability to reject corneal allografts, but are able, in most cases, to reject allogeneic skin grafts. Thus, in the absence of CD4+ T cells, the likely mechanism for rejection appears to involve the generation of CD8+ CTLs.     

Role of CD4+ and CD8+ T cells in murine skin and heart allograft rejection across different antigenic desparities

The factors that influence the relative contribution of the T cell subsets to allograft rejection remain unclear. We compared skin and heart rejection in CD4 Knockout (KO), and CD8 KO mice across full-, minor-, and class II histocompatibility antigen (HA) mismatches. Skin allografts were rejected by either CD4+ or CD8+ T cells alone at any degree of antigenic mismatch. However, either the absence of CD4+ cells or a lesser degree of HA mismatch resulted in prolongation of graft survival. In contrast, fully allogeneic heart grafts were accepted in CD4 KO recipients, and minor HA mismatched heart grafts were accepted by both CD4 KO and CD8 KO mice. Thus, the T cell subsets required for allograft rejection are determined by the immunogenicity of the tissue transplanted. In the absence of CD8+ T cells, perforin and Fas ligand (FasL) but not granzyme B mRNA were detected in rejecting grafts. Thus, granzyme B is a CD8+ cytotoxic T lymphocyte (CTL)-specific effector molecule.