A macrophage-derived factor different from interleukin 1 and able to induce interferon-γ and lymphoproliferation in resting T lymphocytes

A novel monokine different from interleukin 1 (IL-1) is secreted from human or murine macrophages stimulated with galactose oxidase, a well-characterized enzyme able to induce marked polyclonal activation of lymphocytes. This monokine, preliminarly termed macrophage-derived blastogenic factor (MBF), stimulates resting T lymphocytes to produce interferon (IFN)-γ and to proliferate. The apparent MW of MBF ranges between 29,000 and 35,000, although some active fractions show smaller MW ranging from 2000 to 7000, as demonstrated by gel filtration. The biological relationship between MBF and IL-1 was examined and it was found that MBF (1) is able to induce IFN-γ production and proliferation by T lymphocytes in the absence of other inducers, (2) is not able to activate PHA-stimulated C₃H mouse thymocytes, (3) is not able to induce production of IFN-β by fibroblast cultures, (4) is resistant to proteolytic enzymes, and (5) is not neutralized by antibodies to IL-1. MBF was released in the macrophage supernatants in two waves after the oxidation process, namely, after 15 min and 2.5 hr, and each wave was capable of inducing lymphocyte activation at dilutions up to 1:32. Because the oxidation of galactose residues on cell surface structures is considered a general feature of lymphocyte activation whatever the inducer, it seems that MBF may be a mediator involved in mitogenic activation of T cells leading to IFN-γ production and proliferation.