Secretion of a macrophage‐activating factor distinct from interferon‐γ by human T cell clones

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Abstract
Supernatants from clones of human T lymphocytes that were responding to a purified Mycobacterium tuberculosis antigen were able to activate macrophages and macrophage-like myeloma cells (U937) to release increased amounts of the microbicidal agent hydrogen peroxide. The activity was not neutralized by monoclonal antibody against interferon-gamma (IFN-γ), was greater than could be accounted for by the IFN-γ activity in the supernatants, and was separated from IFN-γ by high performance liquid chromatography. It is evident that IFN-γ is not the only macrophage activator released by T lymphocytes responding to microbial antigen, and may not even be the main one to enhance antimicrobial activity in infections such as tuberculosis.