CD200 and B-cell chronic lymphocytic leukemia: To explore whether the elevation of sCD200 in the supernatant of PMA treated CLL cells was a function of inducible ectodomain shedding which followed a similar pattern, CLL cells from a different cohort of patients (n = 6) were monitored by FACS for CD200 expression on the cell surface 24h after PMA stimulation (Fig 3; see also S1a–S1c Fig), and by Western blotting and ELISA using membrane extracts harvested from the same cells (Fig 4a and 4b).