Expression of ABCA1 in SS-parental lymphocytes increased Ca²⁺-stimulated PS exposure on the cell surface. (A) Verification of the elevated level of ABCA1 mRNA in the transduced and G418-selected cell line by RT-PCR. Agarose gel electrophoresis of the PCR products using primers for ABCA1 or ABL and following templates: cDNAs obtained by reverse transcription of total RNA prepared from control EBV-transformed B cells (WT), from the stable SS-ABCA1⁺ cell line, or from the parental EBV transformed SS B cells (SS-parental). The last lane shows a negative control using total RNA prepared from the SS-ABCA1⁺ cells (-RT control) as template for the PCR. (B) Flow cytometry analysis of A23187-induced annexin V*488 binding for control wild-type (WT; top), ABCA1-expressing SS (SS-ABCA1⁺; middle) or SS-parental cells (bottom). Representative experiments show annexin V–Alexa Fluor 488 binding in the absence of A23187 at t₀ (dotted lines), or annexin V–Alexa Fluor 488 binding induced by A23187 for 3 minutes (thin solid lines) or 10 minutes (bold solid lines). Ca²⁺-dependent PS exposure of SS-ABCA1⁺ cells was significantly increased compared to the SS-parental cell line.