Intragraft antigen presentation: The contribution of bone-marrow derived, epithelial and endothelial presenting cells

Tubulitis after renal transplantation: demonstration of an association between CD103+ T cells, transforming growth factor beta1 expression and rejection grade

BACKGROUND

Tubulitis is a defining feature for the diagnosis and management of acute renal allograft rejection. Lymphocytes extracted from rejecting renal tissue are known to express the alphaEbeta7-integrin (CD103), a receptor for E-cadherin expressed on epithelial cells. In this study, expression of CD103 was examined in situ in tubulitis associated with acute rejection.

METHODS

Immuno-labeling detected CD8+ and CD103+ lymphocytes and E-cadherin on epithelial cells in cryostat sections from 34 diagnostic biopsy specimens and a limited number of transplant nephrectomies. CD8+ and CD103+ intratubular cells were enumerated as mean numbers per tubular crosssection and median values were compared between rejection grades as were median ratios of CD103+ to CD8+ cells. Active transforming growth factor (TGF) beta1 was quantified in paraffin sections by immunofluorescence and confocal microscopical analysis. A parallel in vitro study quantified CD103+ T cells after allospecific activation with and without exogenous TGFbeta1.

RESULTS

CD8+ T cells were present in tubules and tubular interstitium in acute rejection. CD103+ T cells were restricted exclusively to the tubules. The numbers of intratubular CD8+ and CD103+ cells and the ratio of intratubular CD103+ to CD8+ cells increased significantly with tubulitis score (P values 0.005, 0.009, and 0.02, respectively). TGFbeta1 expression was wide-spread in tubules also increasing significantly with tubulitis score (P=0.034). In chronic rejection, CD103+ T cells and TGFbeta1 were present within both tubules and interstitial cell populations. The in vitro study demonstrated that addition of TGFbeta1 to activated, alloantigen-specific T cells increased the proportion of CD8+ cells that also expressed CD103.

CONCLUSIONS

These data indicate that specific upregulation of the alphaEbeta7-integrin by activated, intratubular T cells in acute renal allograft rejection could be a consequence of exposure to high local concentrations of TGFbeta1. The capacity of CD103+ T cells to bind E-cadherin on tubular epithelial cells may be an important factor in the pathogenesis of specific tissue damage observed in acute renal allograft rejection.

Species differences in the expression of major histocompatibility complex class II antigens on coronary artery endothelium: implications for cell-mediated xenoreactivity

BACKGROUND

There is controversy in the literature as to whether swine coronary endothelium expresses major histocompatibility complex (MHC) class II antigens constitutively.

METHODS

Because this issue has implications for cell-mediated human anti-swine xenogeneic responses, we stained tissue sections from human, pig, rat, and mouse hearts with the anti-class II monoclonal antibody ISCR3, which has a similar specificity and titer when binding to human, porcine, and rodent class II molecules.

RESULTS

Immunoperoxidase staining of human and porcine hearts with ISCR3 resulted in a dense reaction on the coronary endothelium of epicardial arteries, intramuscular arterioles, and capillaries. In contrast, the coronary endothelium of rat and mouse hearts did not stain with ISCR3. When freshly harvested porcine aortic endothelial cells were placed in culture, class II MHC antigen expression was lost within three to four passages.

CONCLUSIONS

Thus, using a single antibody with cross-species reactivities, we demonstrate that swine coronary endothelium, unlike rodent coronary arteries, expresses similar basal amounts of class II MHC antigens to human coronary vessels. The constitutive expression of class II MHC antigens on swine coronary artery endothelium may contribute to host T cell-mediated xenogeneic responses in clinical pig-to-human cardiac xenotransplantation and thus become a target for therapeutic intervention.