Bone marrow metalloproteinases and neutrophil elastase are induced normally in CXCR4^−/− chimeras. Bone marrow chimeras (n = 2-4 each group) reconstituted with wild-type (CXCR4^+/+) or CXCR4^−/− fetal liver cells were treated with G-CSF or left untreated (ctrl) and bone marrow plasma was isolated. Metalloproteinase (A) and neutrophil elastase (B) activity in the bone marrow plasma was estimated by measuring cleavage of labeled substrate and normalizing for protein content. Data represent mean ± SEM; *P < .05; **P < .01.