Mature mouse mast cells express mouse CD34 but not transgenic human CD34. (A) BMMC cultures were established from wild-type (wt) and hCD34tg bone marrow and assessed for expression of mouse and human CD34 and for c-kit and FcϵRI as markers of mast-lineage cells by flow cytometry. Blue lines indicate wild-type BMMCs; green lines, hCD34tg BMMCs; red lines, secondary antibody alone; and orange lines, human CD34 staining of KG1a cells. (B) Reverse-transcription-polymerase chain reaction (RT-PCR) analysis of BMMCs and KG1a cells for expression of mouse and human CD34 mRNA. Two bands in mouse CD34 lanes correspond to the expected size of the 2 naturally occurring splice variants of mouse CD34 detected by the murine primers.