la-positive T lymphocytes are the producer cells of interferon gamma.
The production of gamma-interferon (IFN gamma) in human peripheral blood T lymphocytes was induced by stimulation with PHA. For identification of the producer cell of IFN gamma, double fluorescence studies were undertaken and titers of interferon were determined in preparatively separated T-cell subpopulations reactive with one of the monoclonal antibodies OKT3, OKT4, OKT8, and OKIal . Production of IFN gamma was found in OKT3+, OKT4+, and OKT8+ cells. However, IFN gamma production occurred only in T cells also reactive with the monoclonal antibody OKIal . Addition of macrophages had no substantial effect on interferon titers in these subpopulations. It is suggested that the T cell subset producing IFN gamma is characterized by its reactivity with the monoclonal antibodies OKT3, OKT4 or OKT8, and OKIal .