Fibrosis-memory is mediated by IL-3-producing T cells and drives progression of fibrosis.

Repetitive injuries are an important trigger of progressive fibrosis. To study if repetitive injuries induce an accelerated profibrotic process, also called "fibrosis-memory," we established an experimental system with two consecutive, clearly separated insults in a model of renal fibrosis with reversible and irreversible unilateral ureteral obstruction. We found that a preceding fibrotic event of one kidney markedly enhanced subsequent development of fibrosis in the contralateral kidney. Aggravation of fibrosis during the second insult was dependent on memory CD4+ T cells. T cell depletion abrogated the fibrosis-memory effect, while adoptive transfer of memory T cells from fibrotic mice enhanced fibrosis in the recipients. Moreover, IL-3 production by memory CD4+ T cells was essential for aggravation of fibrosis in memory situations. In patients with systemic sclerosis, IL-3 expression by T cells was markedly increased, especially after a long disease duration accompanied by involvement of internal organs. In summary, our data identify IL-3-mediated fibrosis-memory as an important driver of progressive fibrosis.