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

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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.

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