Immunocytochemical study of a Ca(2+)-ATPase enzyme in the human megakaryocytic lineage.

We report the presence of a Ca(2+)-ATPase in human megakaryocytes (MK) using an immunofluorescence technique on bone marrow smears and especially on normal MK progenitors in culture. This finding is based on the comparative staining of MK with 1) a well-characterized antibody raised against purified rabbit skeletal sarcoplasmic reticulum Ca(2+)-ATPase, 2) antibody P2 raised against the glycoprotein IIb-IIIa complex as a marker of megakaryocytic lineage, and 3) anti-glycophorin A as a marker of erythroid lineage. On bone marrow smears, all cells recognized by P2 were also labeled with the anti-Ca(2+)-ATPase antibody. In culture, a maximum number of MK colonies was observed at day 11. From days 2-4, some MK precursors appeared stained both with the anti-Ca(2+)-ATPase and P2 antibodies; other cells were reactive with both anti-Ca(2+)-ATPase and anti-glycophorin A antibodies. From day 5 of culture, cells were either simultaneously stained with P2 and anti-Ca(2+)-ATPase antibodies or with anti-glycophorin A antibody, but not with the anti-Ca(2+)-ATPase antibody. Besides this first evidence of an early expression of a Ca(2+)-ATPase in MK, this work provides a useful tool for identification of MK by immunofluorescence.