Strain specific EPO expression analysis in homozygous B-hEPO mice by ELISA. Serum were isolated from wild-type C57BL/6 mice (+/+) and homozygous B-hEPO mice (H/H) and analyzed by ELISA with species-specific EPO ELISA kit. Mouse EPO was detectable in wild-type mice (A). Human EPO was exclusively detectable in homozygous B-hEPO mice but not in wild-type mice (B).