CNTO 530, epoetin-alfa, and darbepoietin-alfa dose-dependent effects on red cell production. (A) In dose-response studies, the capacity of CNTO 530 to stimulate red cell production in wild-type C57BL/6 mice was analyzed and was compared with dose responses for epoetin-alfa (EPO) and darbepoietin-alfa. CNTO 530 and darbepoietin-alfa were as single intraperitoneal injections, whereas epoetin-alfa (EPO) was injected at 1 and 24 hours (as indicated by ). Doses are as microgram or unit (U, EPO) per mouse gram-weight. Hematocrits are mean values ± SE (n = 5). (B) Time-course analysis of CNTO 530–induced red cell and reticulocyte production: Mice were injected with CNTO 530, epoetin-alfa (EPO), or darbepoietin-alfa at near maximal doses (0.15 μg/mouse gram-weight, 1.5 U/mouse gram-weight, and 0.012 μg/mouse gram-weight, respectively). Responses in hematocrits and reticulocytes then were determined on days 4, 8, 12, 16, and 24, and are graphed as mean values ± SE (n = 4).