IN-SITU EXPRESSION OF CYTOKINES IN HUMAN HEART ALLOGRAFTS

Although allograft rejection, the major complication of human organ tr ansplantation, has been extensively studied little is known about the exact cellular localization of the cytokine expression inside the graf t during rejection. Therefore, we used in situ hybridization and immun ohistochemistry to study local cytokine mRNA and protein expression in human heart allografts, in relation to the phenotypical characteristi cs of the cellular infiltrate, Clear expression of mRNA for interleuki n (IL)-6 IL-8, IL-3, and IL-10 and weak, expression for IL-2, IL-4, IL -5, and tumor necrosis factor (TNF)-alpha was detected in biopsies exh ibiting high rejection grades (grade 3A/B), Also at lower grades of re jection, mRNA for IL-6 and IL-3 was present. Some mRNA for IL-1 beta, TNF-beta, and interferon (IFN)-gamma was detected in only a few biopsi es Using immunohistochemistry, IL-2, IL-3, and IL-10 protein was detec ted in biopsies with high rejection grades, whereas few cells expresse d IL-6, IL-8, and IFN-gamma. In biopsies with lower grades of rejectio n, a weaker expression of these cytokines was observed IL-4 was hardly detected in any of the biopsies The level of IL-12 expression was equ al in all biopsies. Although mRNA expression of several cytokines was expressed at a low level compared with the protein level of those cyto kines, there was a good correlation between localization of cytokine m RNA and protein. Expression of IL-2, IL-4, IL-5, TNF-alpha and IFN-gam ma was mainly detected in lymphocytes. IL-3, IL-6 IL-10, and IL-12 wer e not detected or not only detected in lymphocytes but also in other s tromal elements (eg, macrophages). Macrophage production of IL-3 and I L-12 was confirmed by immunofluorescent double labeliag with CD68. We conclude that cardiac allograft rejection is not simply regulated by T helper cell cytokine production, but other intragraft elements contri bute considerably to this process.