Lymphocytosis of Large Granular Lymphocytes

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 termedlarge 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.¹,²Despite their morphologic similarity, immunologic analysis has shown striking heterogeneity in their surface antigens.³,⁴Almost 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.⁵Whether LGLs are derived from the T cell or the myelomonocytic lineage is still not clear. There have been an increasing number