Expression of CD99. (A) Expression of CD99 on the HBMEC line, on human CD14⁺ mobilized peripheral blood (mPB) monocytes, and on mPB CD34⁺ cells (n = 14), on bone marrow CD34⁺ cells (BM, n = 5) and cord blood CD34⁺ cells (CB, n = 4). Error bars represent SEM. The detection of the 2 isoforms, T1 (the full-length form) and T2 (the truncated form), shows the relatively low level of the T2 isoform in mPB CD34⁺ progenitors when compared with mPB CD14⁺ monocytes (a representative illustration of gel electrophoresis of RQ-PCR products for CD14⁺ and CD34⁺ cells immunoselected from the same apheresis sample). (B) Representative flow cytometric detection of CD34 and CD99 expression on immunoselected CD34⁺ progenitors obtained from an adult patient undergoing apheresis.