Functional CCR7 is selectively expressed by bone marrow progenitors. (A) The indicated populations were sorted from WT mice and cDNA was prepared. Real-time PCR was then used to quantify the relative levels of CCR7 transcripts. Shown is the mean ± SEM for 3 independent experiments. (B) Bone marrow (BM) from wild-type (WT) and CCR7^−/− mice were analyzed by flow cytometry for CCR7 expression on the indicated populations. Numbers represent the percentage of WT cells in the indicated gate. (C) For chemotaxis assays, WT BM cells were added to transwells with the indicated chemokines in the bottom and/or top wells. After a 2-hour incubation, the migrated cells were collected and quantified by flow cytometry. Shown is the mean ± SEM for data pooled from 3 experiments. *P < .05 for the indicated condition compared with the no-chemokine control condition. (D) BM from WT mice was analyzed for the coexpression of CCR7 and CCR9. Shown are cells previously gated as LMPPs (left panel) and CLPs (right panel). The gates showing CCR7⁻CCR9⁺, CCR7⁺CCR9⁺, and CCR7⁺CCR9⁻ subpopulations were placed according to CCR7^−/− and CCR9^−/− controls (data not shown). (E) WT and CCR9^−/− BM were analyzed by flow cytometry for CCR7 and CCR9 coexpression. The gray histogram in the third column represents the CCR7^−/− control.