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Limiting dilution analysis of the frequency of human T cells and large granular lymphocytes proliferating in response to interleukin 2. II. Regulatory role of interferon on proliferative and cytotoxic precursors.

Limiting dilution analysis has shown that large granular lymphocytes (LGL) and small T cells undergo proliferation in response to lectin-free IL 2. The latter is critically dependent on prior stimulation with lectin. Depending on conditions, alpha or beta interferons (IFN) were found to have either of two opposing effects on the frequency of proliferating cells. Pretreatment of responder cells with IFN resulted in dose-dependent augmentation of proliferative progenitors such that at 500 IU/ml, a fivefold increase of progenitor frequency was apparent. Under such conditions, approximately 5% of LGL could be expanded, and at least a proportion of the cultured cells killed the NK-sensitive K562 cell line. Similar results were apparent with T cell responders: whatever the initial frequency of proliferation (dependent on the PHA dose), augmentation was obtained with IFN pretreatment, although no killing of K562 was induced. In contrast, when IFN was present throughout the 7-day assay period, proliferative frequencies were reduced. This inhibitory effect was mediated through the presence of irradiated T cells in the feeder populations. With purified monocytes as feeder cells, little reduction was seen, whereas addition of T cells resulted in a 19-fold inhibition. Separation of OKT4+ and OKT8+ subsets demonstrated that both were essential for optimum induction of suppression. These data indicate that IFN has a powerful immunodulatory role on both NK and T cell proliferation, and that it may function both by induction of IL 2 receptors and activation of suppressive T cells. The interaction between different soluble mediators provides a complex immunoregulatory circuit in vitro.