CMRF-44 positive blood DC can be detected before culture. (A) Mature lineage positive mononuclear cells were removed by magnetic immunodepletion. The resulting lineage negative cells were labeled before (0 hours) and after 12 hours culture. A lineage negative, CMRF-44 positive subpopulation is noted. The differential expression of the activation antigens recognized by CMRF-44, HB15a (CD83), and anti-HLA-DR antibodies allow the identification of distinct stages of early DC development (see text). The rectangle indicates the CMRF44⁺/CD83⁻ stage of DC differentiation . (B) Time course labeling of cultured lineage negative cells gated on CMRF-44 positive cells showing the differential expression of the CMRF-44 and CD83 antigens. No CD83⁺/CMRF-44⁻ cells were detected at any time point. Quadrants are placed according to isotype-matched negative controls such that <95% of events are excluded from the right-hand quadrants. Results are from one of three similar experiments.