Calcium ionophore-stimulated PS exposure in murine B cells is ABCA1 independent. Lymphocytes from ABCA1-deficient mice and age-matched controls from the same colony were labeled with anti-CD19^APC and anti-CD19^PERCP antibodies, respectively, mixed and preincubated with AV^FITC or MC540. Histograms show (A) the percentage of CD19⁺ B cells having exposed PS (indicated by binding of AV) following stimulation with 5 μM calcimycin (arrow), or (B) MC540 uptake by CD19⁺ B cells following stimulation with 2.5 μM calcimycin (arrow). ABCA1^-/-, red line; parental, blue line.