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.