Low frequency of infiltrating cells intensely expressing T cell cytokine mRNA in human renal allograft rejection.

Immunosuppressive drugs used in clinical transplantation block cytokine mRNA transcription in vitro, but clinical rejection episodes are common. An understanding of what cytokine message is transcribed would be helpful in determining what contributes to the success of immunosuppression and provide directions for further research aimed at targeting specific cytokines. Previous studies have examined cytokine mRNA in rejecting solid organ biopsies by the reverse transcriptase polymerase chain reaction (RT-PCR) with variable results. We used nonradioactive in situ hybridization with cytokine-specific riboprobes to determine the frequency of cells expressing cytokine mRNA in the allograft infiltrate. Kidney biopsies were obtained from patients receiving protocol biopsies and with clinical evidence of rejection. Fourteen biopsies with a pathologic diagnosis of rejection were studied. Eight showed no cytokine staining, 2 expressed IL-2, and 3 expressed IL-4 and IFN-gamma. The positive cells were present at a low frequency (mean 2, range 1-5 per 10 high-power fields). The proportion of kidney biopsies expressing detectable message for interleukin-2 (IL-2), interleukin-4 (IL-4), and interferon-gamma (IFN-gamma) by in situ hybridization were similar to those reported using RT-PCR. The novel finding is that these cytokines are expressed in a few strongly positive cells in the allograft infiltrate. The vast majority of infiltrating cells are negative. This suggests that either the biopsies were performed when cytokine message was not expressed at a high level or that in human allograft recipients the sustained expression of the cytokines IL-2, IL-4, and IFN-gamma may not be necessary for graft rejection.