Alloantigen-specific CD8(+) T cells stimulate endothelial cells to produce the T-cell chemoattractants IP-10 and Mig

Endothelial cells in allograft rejection

In organ transplantation, blood borne cells and macromolecules (e.g., antibodies) of the host immune system are brought into direct contact with the endothelial cell lining of graft vessels. In this location, graft endothelial cells play several roles in allograft rejection, including the initiation of rejection responses by presentation of alloantigen to circulating T cells; the development of inflammation and thrombosis; and as targets of injury and agents of repair.

Endothelial cells in allograft rejection

In organ transplantation, blood borne cells and macromolecules (e.g., antibodies) of the host immune system are brought into direct contact with the endothelial cell lining of graft vessels. In this location, graft endothelial cells play several roles in allograft rejection, including the initiation of rejection responses by presentation of alloantigen to circulating T cells; the development of inflammation and thrombosis; and as targets of injury and agents of repair.

Effect of CXCL-1/KC production in high risk vascularized corneal allografts on T cell recruitment and graft rejection

BACKGROUND

The survival rate of corneal allografts in high-risk vascularized corneal bed recipients is poor, similar to vascularized solid organ allografts. Although the early induction of selective chemokines in solid organs is required for the optimal recruitment of T cells into rejecting allografts, little is known about the role of these chemokines in high risk corneal allografts.

METHODS

Orthotopic corneal allotransplants were performed in low-risk (nonvascularized) and high-risk (vascularized) C57BL/6 (H-2b) recipients using Balb/c (H-2d) donors. Intragraft production of CXC chemokines was measured by Luminex and enzyme-linked immunosorbent assay on corneal transplant extracts at different times after surgery. Rabbit anti-KC serum was used to test its role in high risk corneal allograft survival.

RESULTS

Early upregulation of CXCL1/KC occurs 3 days after transplantation in high risk allograft only. Moreover, the T-cell chemoattractants, CXCL9/Mig and CXCL10/IP10, are produced late (day 10) after surgery and their production correlates with the recruitment of CD4 T cells into the graft. Furthermore, in vivo neutralization of CXCL1/KC with anti-KC sera results in increased graft survival and decreased recruitment of T cells into high-risk allografts.

CONCLUSION

We propose that a high risk vascularized cornea behaves like a vascularized solid organ transplant. The early production of CXCL1/KC is crucial to the induction of T-cell chemoattractants necessary for the recruitment of allospecific CD4 T cells into the graft. In vivo neutralization of CXCL1/KC represents a potential novel therapy that could be used to increase the survival rate of high-risk vascularized corneal allografts.

Organ-Specific Differences in the Function of MCP-1 and CXCR3 During Cardiac and Skin Allograft Rejection

BACKGROUND

Chemokines are well-established to function in the recruitment of leukocytes into allografts in the course of rejection. Moreover, some studies have indicated that there are organ-specific differences in chemokine function, but the mechanism accounting for this difference is not known.

METHODS

Fully major histocompatibility complex-mismatched vascularized cardiac transplants or skin transplants were performed using BALB/c (H-2d), C57BL/6 (H-2b), MCP-1-/- (H-2b) and CXCR3-/- (H-2b) mice as donors or recipients. Also, skin grafts (H-2b) were placed onto SCID mice (H-2d) that received BALB/c splenocytes (H-2d) by adoptive transfer either at the time of transplantation, or after a period of 28 days.

RESULTS

Cardiac allografts in MCP-1-/- recipients survived significantly longer (P<0.0005) than wild-type (WT) controls. However, there was no prolongation of survival when MCP-1-/- grafts were used a donors in WT mice. In contrast, the absence of donor but not recipient MCP-1 prolonged skin allograft survival. WT donor cardiac grafts in CXCR3-/- recipients had a modest prolongation of survival (P<0.0005), whereas CXCR3-/- donor cardiac grafts in WT recipients were rejected similar to controls. Also, while recipient CXCR3 had no effect on the rejection of skin, CXCR3-/- donor skin grafts survived significantly longer than WT controls. This survival advantage was lost when vascularized CXCR3-/- skin grafts were used as donors in the SCID model of rejection.

CONCLUSION

Recipient derived MCP-1 and CXCR3 are functional in the rejection of vascularized, but not nonvascularized, allografts. In contrast, donor-derived MCP-1 and CXCR3 are functional in nonvascularized, but not vascularized grafts.

CXCL9 antagonism further extends prolonged cardiac allograft survival in CCL19/CCL21-deficient mice

CCL19/MIP-3beta and CCL21/SLC are essential for chemotactic recruitment of mature dendritic cells (DC) to T-cell areas of secondary lymphoid tissue. Paucity of lymph node T-cells (plt/plt) mice lack CCL21-serine (ser) and CCL19 expression. We tested plt/plt and wild type (wt) BALB/c (H2d) mice as recipients of heart or skin allografts from C57BL/10J (H2b) donors. Donor DC trafficking to secondary lymphoid tissue was markedly reduced in plt heart but not skin allograft recipients. Heart, but not skin grafts survived significantly longer in plt recipients. Accordingly, T cells from plt heart transplant recipients demonstrated poor anti-donor responses in ex vivo MLR, compared to wt heart or wt and plt skin recipients. Moreover, donor-reactive T cells from plt heart recipients exhibited Th2-skewing in comparison to T cells from wt heart or skin graft recipients. Anti-CXCL9/Mig was administered for 2 weeks post-transplant to determine whether impairment of activated T-cell migration could further prolong cardiac allograft survival in plt recipients. CXCL9-antagonism extended graft survival significantly only in plt mice, likely due, in part, to retention of alloactivated T cells in secondary lymphoid tissue/reduction of graft-infiltrating T cells. Thus, targeting DC and activated T-cell migration concomitantly has additive effects in prolonging heart graft survival with potential for therapeutic application.

Induction of Fractalkine and CX3CR1 Mediated by Host CD8+ T Cells in Allograft Tolerance Induced by Donor Specific Blood Transfusion

BACKGROUND

Donor-specific tolerance to heart allografts in the rat can be achieved by donor-specific blood transfusions (DST) before transplantation. This tolerance induction requires the presence of host CD8 T cells and is characterized by the infiltration of numerous leukocytes.

METHODS

To identify new mediators involved in tolerance induction, gene searching was performed and resulted in the identification of the Fractalkine receptor, CX3CR1, as being highly expressed in tolerated allografts.

RESULTS

We showed that the high CX3CR1 mRNA accumulation found in tolerated allografts was related to the active recruitment of monocytes/macrophages. CX3CR1 transcript accumulation was preceded by an early expression of its ligand, Fractalkine, by graft endothelial cells. Interestingly, depletion of recipient CD8 cells led to a dramatic decrease in both CX3CR1 and Fractalkine mRNA levels. Moreover, in vitro, CD8 T cells from DST-primed animals were found to strongly induce Fractalkine expression in an allogeneic endothelial cell line.

CONCLUSION

This is the first report describing Fractalkine, a chemokine usually described in inflammatory processes, as being expressed in a model of allograft tolerance.

Alloimmune induction of endothelial cell-derived interferon-gamma-inducible chemokines

BACKGROUND

The interaction between host lymphocytes and endothelial cells on the transplanted organ is believed to play an important role in acute and chronic graft rejection. Trafficking and recruitment of lymphocytes to the site of inflammation is known to be controlled by several cytokines and chemokines. It is unclear whether endothelial cells themselves can be a source of inflammatory chemoattractant molecules on alloimmune induction.

METHODS

Using a semiquantitative polymerase chain reaction method, the authors analyzed the expression of chemokine mRNA coding for interferon (IFN)-gamma-induced protein 10 (IP-10) and monokine induced by IFN-gamma (Mig) in a pool of human aortic endothelial cells. Both of these chemokines are known to be induced by IFN-gamma. Endothelial cell-derived chemokine mRNA was assayed at rest, after IFN-gamma activation, and after co-culture with allogeneic peripheral blood mononuclear cells (PBMC) from normal blood donors with and without a monoclonal antibody to IFN-gamma. Finally, protein release into the media was assayed using an enzyme-linked immunosorbent assay to IP-10.

RESULTS

Mig and IP-10 were expressed in human endothelial cells both after IFN-gamma treatment and after PBMC co-culture. Furthermore, the expression of both of these endothelial cell-derived chemokines was dependent on IFN-gamma because PBMC-induced expression was blocked with anti-IFN-gamma. IP-10 levels in the endothelial cell supernatant increased from a baseline of 13.4+/-10.8 pg/mL to 299.5+/-13.4 pg/mL (P<0.0001) with exposure to PBMC and was likewise inhibited by anti-IFN-gamma A-b (33.8+/-17.8 pg/mL).

CONCLUSIONS

Vascular endothelial cells are capable of producing inflammatory chemokines when activated and potentially serve to amplify the allogeneic response.