Characterization of PECAM-1 expression on leukocyte tumor cell lines. The human leukocyte cell lines HEL, Dami, and Raji were examined for PECAM-1 expression. (A) Flow cytometric analysis of PECAM-1 expression. Cells were stained with either normal rabbit IgG or the human PECAM-1–specific polyclonal rabbit IgG, SEW16. Detection was accomplished by staining with a dichlorotriazinyl amino fluorescein-conjugated goat antirabbit IgG. As shown, HEL and Dami cells, express PECAM-1 on their surface, whereas Raji cells are negative. (B) Western blot analysis of PECAM-1 expression in HEL, Dami, and Raji cells was performed using SEW16. Detection was accomplished using alkaline phosphatase-conjugated goat antirabbit secondary antibody. Note that Raji cells do not contain even an intracellular pool of detectable PECAM-1. (C) RT-PCR analysis of PECAM-1 mRNA levels. mRNA was isolated from HEL, Dami, and Raji cells and subjected to RT-PCR using primers spanning a 400-bp region of PECAM-1 that include exons 2 and 3. These primers would yield a PCR product of greater than 12-kb product if amplification were to occur from genomic DNA. As shown, both HEL and Dami cells express PECAM-1 mRNA, whereas Raji cells are negative.