CCR2 and pulmonary fibrosis: CCR2 is also highly expressed on cells of the mononuclear phagocyte lineage including monocyte, macrophage and dendritic cell populations, however, and reduced lung fibrosis in response to bleomycin in CCR2 knockout animals correlated with a substantial reduction in these cells as well as inflammatory cytokines in the bronchoalveolar lavage fluid [31,32]; it is therefore not clear whether the observed effect in CCR2-deficient animals is attributable to fibrocytes or other cell populations.