Differential in situ expression of cytokines in renal allograft rejection

The expression of the interleukin 6, tumor necrosis factor alpha, and interferon gamma (IFN-gamma) genes was studied in human renal biopsies from individuals without evidence of kidney disease and from patients undergoing acute renal allograft rejection using a method of in situ hybridization capable of detecting 1-5 copies of a specific cellular messenger RNA in individual cells. IL-6, TNF-alpha, and IFN-gamma RNA transcripts were not detected in any of the sections of normal human kidneys. Elevated levels of IL-6 mRNA but not IFN-gamma were, however, detected in the sections of the renal biopsies from six of eight patients exhibiting acute rejection. A uniform level of expression of IL-6 mRNA was observed in all the cells examined, including glomerular cells, tubular epithelia, smooth muscle cells, and vascular endothelia, as well as the interstitial mononuclear infiltrate. Juxtatabular clusters of TNF-alpha mRNA were detected in the absence of IL-6 mRNA in one patient exhibiting acute rejection. Only a small number of grains (1-5 per high-power field) was detected in the urinary space or in the tubular or vascular lumen following hybridization with the IL-6 or TNF-alpha probes. In contrast, in kidney transplant patients with stable renal function no significant labeling was observed with the IL-6, TNF-alpha, or IFN-gamma probes. A similar level of expression of actin mRNA was observed in all the sections of normal and transplanted kidneys studied, suggesting that the overall level of RNA synthesis was similar in both groups. These results suggest that cytokines such as IL-6 play a role in acute allograft rejection.