A possible mechanism of immunoregulation produced by alpha 2-macroglobulin.

Most of the plasma suppressive activity was associated with alpha 2M in both normal subjects and cancer patients. alpha 2M binding to physiological levels of proteases was associated with an increase in the ability to suppress lymphocyte reactivity in the TEEM test. alpha 2M binding to proteases released a peptide that was a component of the alpha 2M; this peptide suppressed lymphocyte reactivity to mitogenic, antigenic, and allogenic stimuli in the TEEM test and in the lymphocyte transformation assay. Physically and biologically similar peptides have been found in the plasma of cancer patients and patients with thermal burns, uremia, and acute pancreatitis.