Immuno-electron microscopic characterization of large granular lymphocytes (natural killer cells) from rat liver.

The immunocytochemical characteristics of large granular lymphocytes (LGL), isolated from the liver sinusoids of euthymic and athymic (nude) rats, were investigated in electron microscopy by the immunoperoxidase technique. The LGL were found positive for MRC OX-8 (natural killer cells and cytotoxic/suppressor T cells) and negative for MRC OX-19 (pan-T marker) in both rat strains. The LGL were heterogeneous in the expression of the natural killer cell marker asialo-GM1 which was found on 56% of the LGL from euthymic and on 71% of the LGL from athymic rats. LGL were easily distinguished from the other cells in the preparations, "conventional" lymphocytes and monocytes, thanks to their highly characteristic ultrastructural features, in particular by the presence of specific electron-dense cytoplasmic granules and rod-cored vesicles. These features have been described formerly for the so-called "pit cells" and are more reliable than the classical LGL characteristics at the light microscopic level, i.e. the presence of azurophilic granules. Our results give further support for the existence of an important population of natural killer cells in the liver sinusoids.