Effect of dexamethasone erythroid output and Epo sensitivity of normal and DBA cultures. Dexamethasone enhances erythroid output of normal and DBA cultures and increases Epo sensitivity. (A) Total number of hemoglobinized (DAF⁺) cells (mean ± SEM) generated after 7 days in phase 2 of culture in different concentrations of Epo (normal, n = 5; DBA, n = 4), normalized to the number of nonadherent cells plated at start of phase 2. (B,C) Representative individual Epo log-dose response curves for normal (B) and DBA (C) cultures, with (•) and without (○) dexamethasone (note the different y-axis scales for normal and DBA cultures). Note the failure of higher concentrations of Epo to enhance erythroid output in the DBA culture. (D) Standardized Epo log-dose response curves for normal and DBA cultures with dexamethasone. Response expressed as percentage (mean ± SEM) of DAF⁺ cells at standard Epo (2 U/mL) for individual cultures shown in panel A, to correct for difference in amplitude of erythroid output between normal and DBA cultures. All cultures are serum-free liquid culture with IL-3/SCF with or without 10^-7 M dexamethasone in both phases, plus 0 to 10 U/mL Epo in phase 2.