We have reported that lung allograft rejection involves an immune response to a native protein in the lung, type V collagen (col(V)), and that col(V)-induced oral tolerance prevented acute and chronic rejection. In support of these findings col(V) fragments were detected in allografts during rejection, but not in normal lungs. The purpose of the current study was to isolate and characterize col(V)-specific allograft-infiltrating T cells and to determine their contribution to the rejection response in vivo. Two col(V)-specific T cell lines, LT1 and LT3, were isolated from F344 (RT1lv1) rat lung allografts during rejection that occurred after transplantation into WKY (RT1l) recipients. Both cell lines, but not normal lung lymphocytes, proliferated in response to col(V). Neither LT1 nor LT3 proliferated in response to alloantigens. LT1 and LT3 were CD4+CD25− and produced IFN-γ in response to col(V). Compared with normal CD4+ T cells, both cell lines expressed a limited V-β TCR repertoire. Each cell strongly expressed V-β 9 and 16, but differed in expression of other V-βs. Adoptive transfer of each cell line did not induce pathology in lungs of normal WKY rats. In contrast, adoptive transfer of LT1, but not LT3, caused marked peribronchiolar and perivascular inflammation in isograft (WKY) lungs and abrogated col(V)-induced oral tolerance to allograft (F344) lungs. Collectively, these data show that lung allograft rejection involves both allo- and autoimmune responses, and graft destruction that occurs during the rejection response may expose allograft-infiltrating T cells to potentially antigenic epitopes in col(V).

Immunity to collagen V [col(V)] contributes to lung 'rejection.' We hypothesized that ischemia reperfusion injury (IRI

Interactions between antigen-presenting cells and T cells can result in T cell activation or suppression. With the use of RNA analysis, high-performance liquid chromatography, mixed leukocyte reactions (MLRs), and animal models, the current study reports that lung interstitial antigen-presenting cells (iAPCs, CDllc+) suppress T cell responses in vitro and in vivo by production of indoleamine 2,3-dioxygenase (IDO), an enzyme that catabolizes tryptophan to its byproduct, kynurenine. IDO mRNA expression was unique to lung iAPCs, as cells similarly isolated from the liver and spleen did not express IDO constitutively, or in response to interferon-gamma. Lung iAPCs suppressed proliferation of allogeneic T cells, correlating with increased kynurenine levels; and blockade of IDO activity with 1-methyl-DL-tryptohan (1-MT) or addition of exogenous tryptophan recovered T cell proliferation in MLRs. In contrast, liver and splenic iAPCs were potent stimulators of T cells in MLRs, and IDO inhibition had no effect on T cell responses. In vivo studies showed that systemic blockade of IDO resulted in spontaneous proliferation in lung T cells and pulmonary inflammation. Finally, overexpressing IDO in lung transplants abrogated acute allograft rejection, a T cell-mediated disease. Collectively these data show that lung iAPCs contribute to local regulation of cellular immune responses by production of IDO.