VCAM-1 is expressed in proliferating myeloid cells in vitro from BM or PB, but not in proliferating lymphoid cells. Mononuclear cells from the bone marrow or peripheral blood, or cells isolated from the spleen of VCAM-1^f/f or VCAM-1^Δ/Δ mice were cultured for up to 7 days as described in “Materials and methods.” Total RNA was isolated and reverse transcribed using oligo-dT primer. PCR was performed using long VCAM-1 isoform-specific primers (7D), GPI-linked VCAM-1 isoform-specific primers (GPI), and actin-specific primers as internal controls. Note that cultured PB cells express VCAM-1 mRNA only after 3 to 6 days in culture with cytokines, but not before, whereas BM cells express VCAM-1 both before and after culture (BM^f/f day 0 and day 7). Of interest, cells from the spleen show expression of the 7 domain (full-length) form of VCAM-1 before culture, likely attributed to myeloid cells in spleen, but not after culture under lymphoid conditions. Lymphoid cells proliferating under the stimulus of IL-7 and IL-2 display only the GPI-anchored form.