Regulation of CXCR4 expression by γ-IFN. Freshly isolated BMMNC in serum-free media were either left alone or treated with a variety of proinflammatory cytokines as indicated for 36 hours. Expression of CXCR4 was monitored by FACS analysis after the treatment period. The negative isotype control is overlaid on each histogram. A representative experiment is shown of three independent repeats with similar results. M1 represents the positive population; the percentage of positive cells is indicated within each histogram.