To determine whether CD8+ T cells interact with CD4+ T cells to exert their effect during fibrosis, CD4+ T cells were depleted in CD8 KO mice or CD8+ T cell–reconstituted CD8 KO mice by using a monoclonal CD4 Ab to examine fibrotic areas and fibrosis-related protein levels in UUO kidneys [13]. The gene discussed is CD8A; the disease is fibrosis.