EXPRESSION AND VISUALIZATION DURING CELL-CYCLE PROGRESSION OF ALKALINE-PHOSPHATASE IN B-LYMPHOCYTES FROM C3H HEJ MICE/

The expression of alkaline phosphatase (APase) activity by purified B cells from lipopolysaccharide (LPS)-hyporesponsive C3H/HeJ mice was de termined. Optimal APase activity was expressed after costimulation wit h interleukin-5 and dextran sulfate (DXS), whereas LPS, which is highl y effective on B lymphocytes from normal mice, was unable to induce en zyme expression, even in the presence of DXS. The simultaneous determi nation by flow cytometry of both cellular APase, by using a fluorescen t azo dye technique, and DNA content showed that APase was highly expr essed by about one-tenth of cells in G1 phase, whereas it was present in more than 50% of cells in S and G2/M phases. The enzyme, as visuali zed by confocal microscopy after cell sorting on the basis of DNA cont ent, was found to be, localized mainly in vesicular structures distrib uted throughout the cytoplasm in G1 cells. It was distributed in patch es and essentially localized at the cell periphery in S cells, whereas clear capping of activity was observed in G2/M cells.