Signal transduction in lymphocytic and myeloid cells via CD24, a new member of phosphoinositol-anchored membrane molecules.

The CD24 Ag is present on human B cells from the earliest stages of B lineage development and is lost on terminal B cell maturation to plasma cells. This Ag is also expressed on mature forms of granulocytes. We studied the effects of CD24 mAb on the function of both lymphocytic and myeloid cell types. We found a clear-cut increase in free cytoplasmic calcium when tonsil B cells or mononuclear cells from B cell chronic lymphatic leukemia patients were preincubated with CD24 mAb and further stimulated with goat F(ab')2 anti-mouse Ig antibodies. The same experimental setting with granulocytes instead of B lymphocytes led to the triggering of hydrogen peroxide production in these cells. CD24 Ag is expressed at higher levels on activated granulocytes and is anchored to the plasma membrane by a phosphoinositol linkage. In conclusion we provide evidence that the CD24 Ag are functional molecules in cells of different lineage, playing a signal transducing role in cell function.