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Generation of T cell blasts with NK-like activity in human MLC: Cellular precursors, IL 2 responsiveness, and phenotype expression

Abstract:

Human MLC were separated after 5 to 7 days of culture by Percoll density gradient centrifugation into blasts and small-medium lymphocyte fractions and then were tested for specific cytotoxic alloreactivity, as well as for NK-like activity. The specific alloreactivity was confined to the blast-enriched fraction, whereas the NK-like activity was mediated by both the blasts and the small-medium lymphocyte fraction. The NK-like activity of the blast and of the small-medium lymphocyte fractions differ in the following respects. 1) Cellular precursors: MLC responding cells lacking Fc (7S) receptor-bearing cells at the initiation of the culture did not develop NK-like activity in the small-medium lymphocyte fraction, but on the contrary, they showed strong NK-like activity in the blast fraction. 2) IL 2 responsiveness: External supplementation of MLC cultures with supernatants containing IL 2 induced a strong augmentation of the NK-like activity of the blast fraction, but did not significantly change the cytotoxic activity of the small-medium lymphocyte fraction. The phenotype of the blast cells exerting NK-like and specific alloreactivity was analyzed after their expansion for 6 to 9 days with IL 2 Sup. The blast fraction was comprised almost exclusively of T cells (93% OKT3) with presence of both OKT4 (57%) and OKT8 (34%) subsets. The specific alloreactivity was completely abrogated by treatment with OKT8 and complement (C), whereas the NK-like activity was not diminshed by treatment with either OKT4 or OKT8 and C. Our results indicate that in the MLC there is generation of T cell blasts with NK-like activity that have different cellular precursors and IL 2 responsiveness than the MLC effector cells with NK activity present in the small-medium lymphocyte fraction.