Effects of in vitro incubation in normolipidemic serum on reticulocytes from phlebotomized wild-type mice and erythrocytes from

SR-BI^−/−/apoE^−/−mice. Erythrocytes from wild-type mice with phlebotomy-induced reticulocytosis (panels A-B) and fromSR-BI^−/−/apoE^−/−mice (panels C,E) were incubated in vitro in medium containing 20% normolipidemic fetal calf serum for 0 hours (panels A,C) or 72 hours (panels B,E); the cells were then analyzed by transmission electron microscopy. The red asterisks show membrane-enclosed, cytoplasmic vesicles that appeared to be undergoing expulsion from theSR-BI^−/−/apoE^−/−erythrocytes (panel E). Arrows denote cell-free vesicles found in the incubation medium (panel E). Arrowheads show structures in reticulocytes from phlebotomized wild-type mice that appear similar to the cytoplasmic vesicles seen inSR-BI^−/−/apoE^−/−erythrocytes (panels A-B). Panels D and F show flow cytometry analysis of RNA content (thiazole-orange staining) versus forward scatter of the cells (FSC) forSR-BI^−/−/apoE^−/−samples at 0 hours (panel D) and 72 hours (panel F).