${alpha}2-macroglobulin$ $({alpha}2-M)$ has been shown to have a variety of activities. One of those activities is the suppression of immune response. Characterization of the immunosuppressive factor secreted by a T cell hybridoma showed that ${alpha}2-M$ was produced and secreted from the T cell hybridoma. ${alpha}2-M$ was produced abundantly from the T cell hybridoma when cultured as ascites. The isolation and identification of the ${alpha}2-M$ were studied using affinity chromatography and N-terminal amino acid sequencing. The extended observations were that the ${alpha}2-M$ produced by the T cell hybridoma suppresses mixed lymphocyte reaction.