Proliferation of factor-independent FDC-P1 cells infected with novel constitutive hβc mutants. (A) Proliferation assay of FDC-P1 cells, infected with the indicated hβc mutants, which had been selected before assay for growth in the absence of factor. Also shown are uninfected cells (uninf) that were washed and assayed in medium with (+) and without (−) mGM-CSF. Cells (103) were plated in triplicate and cell proliferation was measured at 72 hours as described in Materials and Methods. The mean and standard error of each triplicate is shown. (B) Flow cytometric analysis of constitutive hβc mutant expression on the factor-independent FDC-P1 cells depicted in (A). Cells were stained by standard indirect immunofluorescence; dashed lines represent cells stained with an irrelevant control antibody and solid lines indicate staining with an anti-hβc antibody. Cell number and fluorescence are in arbitrary units; the latter is plotted on a logarithmic scale. Also shown are analyses of uninfected FDC-P1 cells. Note that data for only the novel mutants isolated in this study are shown.
