Proliferative responses of BaF3/PAR-2 cells to α- (A) or β-tryptases (B). BaF3/PAR-2 cells were plated as outlined in the legend to Fig 1 and incubated with variable amounts of α- or β-tryptases (in the absence of WEHI supplement) for 48 hours before functional evaluation (1 U/L tryptase is equivalent to ∼30 pmol/L). No proliferative responses were evident using mock-transfected BaF3 cells. Likewise, mock-transfected COS-1 supernatants or extracts diluted 1:1 vol/vol with BaF3/PAR-2 cells failed to show any proliferation (not shown). Results represent the mean ± SEM of four wells from a representative set of experiments.