Flow cytometry analysis of cell surface markers. a) Wildtype U937 cells, pMTH1-U937 and asCD11b-U937 were compared with respect to the expression of the CD11b antigen in both, steady-state culture and following a 72 h exposure to 5nM TPA. An IgG1 subclass staining serves as a control which was not altered in the different populations. b) Untreated pMTH1-U937 (pMTH1) and untreated asCD11b-U937 (asCD11b) cells were cultured in either uncoated or 2% (w/v) agarose-precoated cell culture dishes. Following 72 h of incubation with 5nM TPA, respectively, the cells were harvested and flow cytometry analysis was performed in the different populations with the β2-integrin subunit antibodies CD11a, CD11c and CD18 as well as with the monocytic differentiation markers CD14 and F4-80. The relative fluorescence intensity represents the fold induction which has been normalized separately for the appropriate control cell population. Data represent the mean ± s.d. of three measurements.