Complement Receptor Distinguishes between Two Subsets of Large Granular Lymphocytes with Different Natural Killer Activity and Cytochemical and Ultrastructural Features

Abstract

Human peripheral blood large granular lymphocytes (LGL)—that is, cells with intracytoplasmic azurophilic (electron-dense) granules, with a positiviiy for the cytochemical localization of certain acid hydrolascs, and with avid surface receptors for the Fc portion of IgG—have been purified on Percoll density gradients. Approximately 30% of these cells expressed receptors for the third complement component (C3R). They were separated into C3R-positive and C3R-negative cells. C3R⁻ cells had a significantly greater natural killer (NK) activity against K562 target cells than C3R⁺ cells. This difference was unrelated to the presence in the C3R+ cells of a contaminant cell type incapable of NK activity, since cytochcmical and ultrastructural analysis revealed that C3R⁺ and CR⁻ fractions contained comparable LGL numbers. Agarose cytotoxicity assays at the single-cell level demonstrated that C3R ⁺ LGL contained a large number of cells that bound to but did not lyse the target. The remaining fully cytotoxic C3R⁺ LGL had, however, the same killing and recycling properties as the cells from the OR fraction. Electron microscopy and cytochcmical studies showed that C3R⁺cells had fewer electron-dense granules than C3R cells and stained more faintly for the localization of α-naphtyl acetate eslerase. In contrast to C3R cells. C3R⁺ LGL displayed morphological features suggesting that an active process of granule formation was taking place. Taken together, the data indicate that C3R⁺ cells represent a discrete subset or a maturationsl stage of LGL.