In normal human peripheral blood, there is a population of large lymphocytes with slightly eccentric nuclei and abundant pale-blue cytoplasm containing many azurophilic granules. These lymphocytes have been termed large granular lymphocytes (LGLs). It is now clear that almost all natural-killer and antibody-dependent cell-mediated cytotoxic activity resides in this population of cells.1,2 Despite their morphologic similarity, immunologic analysis has shown striking heterogeneity in their surface antigens.3,4 Almost all of these cells bear surface receptors for the Fc fragment of IgG, but some express antigens generally found on T-lymphocytes. Others show surface antigens carried by myelomonocytic cells. This may indicate the presence of multiple distinct subpopulations of cells or a single population of cells expressing different surface antigens at different stages of maturation or functional activity.5 Whether LGLs are derived from the T cell or the myelomonocytic lineage is still not clear.
There have been an increasing number