Enhancement of growth of polyclonal populations of R6-X M-Ras G22V by IL-4. Polyclonal populations of R6-X M-Ras G22V (closed symbols) or of parental cells (open symbols) were plated at 500 cells per well in 96-well plates in medium alone (▴, ▵) or medium supplemented with decreasing amounts of synthetic IL-3 starting at 2 μg/mL (•, ○) or recombinant IL-4 (10 ng/mL) (▪, □). Cell numbers were assessed at day 6 by uptake of MTT. Results are shown as optical densities (OD) of triplicate cultures ± SEM.