Open Collections

Abstract

The maturation of cytotoxic T lymphocyte (CTL) effectors from CTL precursors (CTLp) requires specific signals mediated through cellular interactions and soluble factors. The most studied factor is T cell growth factor (TCGF) which is also termed interleukin-2 (IL-2). This lymphokine is produced by T helper cells (TH) and induces activated CTLp to proliferate and differentiate. However, in the absence of mitogen or antigen stimulation, IL-2 alone cannot induce CTL (except in the case of very high cell density). A factor is described that is found in the supernatant of 4-β-phorbol-12-myristate-13-acetate (PMA)-induced EL4 cells that can polyclonally activate CTL in the presence of IL-2. This factor elutes at 27 kilodaltons (KDa) on a G-100 column, and its target cell includes T cells of the Thyl⁺ Lyt2⁺ L3T4⁻ phenotype. The factor increases the frequency of IL-2 receptor expressing cells within a population, thereby increasing the response to IL-2. It is suggested that this factor acts through an alternative pathway of CTL activation which is independent of specific stimulation by antigen.