We have advanced the hypothesis that the primary autolymphoproliferative response of dog T cells in mixed lymphocyte kidney cultures (MLKC) results from their recognition of tissue-specific (kidney-associated) antigen(s) presented in conjunction with class II MHC antigens. Lymphocyte culture—derived supernatants had been found previously to upregulate class П antigen expression on kidney cells and enhance T cell activation. In the present study we have isolated and characterized dog IFN-7, a class П-inducing substance that is secreted in the culture supernatant of activated T lymphocytes. Dog IFN-7 was induced with A-23187 and PMA and purified stepwise using controlled-pore glass, Mono Q anion exchange chromatography, and Superose в-gel filtration on FPLC. The purification resulted in two molecules of 42 Kd and 31 Kd molecular weights. An IgGl monoclonal antibody was engendered to these molecules. With this mAb reagent, in immunochemical experiments, we have developed a sensitive ELISA and a method for purifying dog IFN-7 by affinity chromatography. Species specificity studies indicated that purified dog IFN-7 reacted with a polyclonal rabbit antihuman IFN-7, but not with a mAb to human IFN-7. However, the antidog IFN-7 mAb that was generated also reacted with recombinant human IFN-7. In in vitro biological studies, the purified IFN-7 (two mol. wt. species) upreg-ulated the expression of canine class П MHC molecules on dog tubular epithelial cells and the dog kidney epithelial cell line (MDCK). The antidog IFN-7 mAb blocked T cell proliferative response to kidney cells and, by inference, the interaction between endogenously released IFN-7 in vitro with its cell surface receptor, thus inhibiting the induced upregulation of class II. Interestingly, although antidog IFN-7 markedly blocked the MLKC (10 tig mAb/well), there was no effect on the allogeneic MLC. This observation indicates that the cytokine IFN-7 may be a uniquely key substance amplifying the immune response of T cells to tissue-associated antigens on surrogate antigen-presenting cells that require induced upregulation of class П MHC antigen expression (MLKC), in contrast to reactions in which these antigens are already constitutively expressed on the antigen-presenting cells (mixed lymphocyte culture).
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