Naturally cytotoxic tonsillar lymphocytes: A manifestation of heterogeneity among human NK cells

Lymphocytes isolated from human tonsils are capable of lysing cells of the natural killer (NK)-susceptibile line K562. Although weak compared with that of autochthonous peripheral lymphocytes, cytotoxicity is invariably manifest at high effector-to-target ratios. Like peripheral NK cells, tonsillar cytotoxic lymphocytes possess a low buoyant density, which makes possible their partial enrichment from non-cytotoxic cells by centrifugation on discontinuous Percoll gradients. However, examination of cytotoxic fractions indicates that, unlike blood lymphocyte-mediated cytotoxicity, effector function is not associated with the presence of large granular lymphocytes. Furthermore, a functional distinction from classical NK cells is apparent since, although tonsillar cytotoxicity is significantly enhanced after exposure to supernatants from polyclonally activated allogeneic tonsils, pretreatment with lymphoblastoid (Namalva) interferon (IFN-α) at doses shown to potentiate maximally the cytotoxicity of peripheral blood lymphocytes fails to influence reactivity. These data provide preliminary evidence for the existence of, at least limited, heterogeneity among human NK cells.