The relationship of CD5 B lymphocytes to macrophages: Insights from normal biphenotypic B/macrophage cells

For decades, numerous investigators have reported derivation of macrophage-like cells from CD5 pre-B cell lymphomas. Recently, it has become clear that biphenotypic CD5 B/macrophage cells are not a spurious result of malignancy. Indeed, the existence of normal biphenotypic cells with CD5 B lymphocyte and macrophage characteristics has been demonstrated in the mouse. This review considers normal B/macrophage cell function in an evolutionary context where a primitive, flexible cell type could perform dual roles in adaptive and innate immunity.