Interferon‐γ and Donor MHC Class I Control Alternative Macrophage Activation and Activin Expression in Rejecting Kidney Allografts: A Shift in the Th1‐Th2 Paradigm

Organ allografts deficient in interferon‐γ (Ifng) or major histocompatibility complex (MHC) class I products develop accelerated necrosis when rejection develops, depending on perforin and granzymes. Thus Ifng‐induced donor class I products deliver inhibitory signals to host inflammatory cells. We used microarrays to investigate whether Ifng‐induced donor class I products also control inflammation patterns in mouse kidney allografts. Compared to wild‐type (WT) allografts, many transcripts were increased in both Ifng‐deficient allografts (Ifng‐suppressed transcripts [GSTs]) and class I‐deficient allografts (class I‐suppressed transcripts [CISTs]), with 73% overlap between GSTs and CISTs. Some GSTs and CISTs reflected increased necrosis, including known injury‐induced transcripts. However, many GSTs and CISTs were independent of perforin, granzymes and necrosis, and were associated with alternative macrophage activation (AMA) (e.g. arginase I [Arg1], macrophage elastase [Mmp12] and macrophage mannose receptor 1 [Mrc1]). AMA transcripts were induced despite absence of host interleukin (IL)4 and IL13 receptors. The AMA inducer may be activins, whose genes (inhibin A [InhbA] and inhibin B [InhbB]) were increased in all allografts with AMA. We conclude that in allograft rejection, Ifng acts via donor Ifng receptors (Ifngr) to induce donor class Ia and Ib products, which engage host inflammatory cells to limit perforin‐granzyme‐mediated damage and prevent AMA associated with inhibition of activin expression. Thus, Ifng may control T helper type 2 (Th2) cell inflammation by induction of class I products.