A mouse plasma substance carrying beta2-microglobulin activity and lacking in H-2 alloantigenic activity.

A mouse plasma substance carrying beta-2-microglobulin activity and lacking in H-2 alloantigenic activity was separated from the blood plasma of A/J strain female mice. The plasma substance had a molecular size of about 300,000-400,000 daltons and an electrophoretic mobility of alpha-globulin. The plasma substance was split by papain digestion to a fragment of about 50,000-60,000 daltons that still carried beta2-microglobulin activity. The papain-split plasma substance was devoid of H-2 alloantigenic activities and Thy-1 and TL alloantigenic activities as well, but yet had a two-component structure that was similar to papain-solubilized H-2 molecules. It contained a 37,000-dalton component linked non-covalently to an 11,00-dalton component, i.e. mouse beta2-microglobulin. This plasma substance appears to be different from Ss protein or Slp protein, both found in mouse serum.