Recruitment of CCR2⁺ cells to the lung after allogeneic BMT. Animals received BM transplants as in Figure 1. CCR2 mRNA was determined after BMT by RNase protection assay. (A) CCR2 mRNA expression in the lungs of allogeneic recipients (▪) was elevated by week 2 and continued to rise over time through week 6 compared with syngeneic controls (□). Data are presented as mean ± SEM and are from 3 to 6 animals per group. (B) CCR2 protein expression is increased on monocytes and macrophages recruited to the alveolar space after allogeneic BMT. (C) F4/80⁺ macrophages in the BALF show a phenotype previously described for newly recruited monocytes to the alveolar space (F4/80⁺/CD11b⁺).^44,45  Thin line indicates isotype control; open histogram, syngeneic; and shaded histogram, allogeneic.