Characterization of Ia antigens in mouse serum

Sera obtained from normal B10.BR mice were shown to inhibit selectively a specific anti-Ia alloantiserum. Partial purification of the Ia antigenic activity was accomplished by isolation of the high density lipoproteins from these sera by fractional precipitation with sodium phosphotungstate and MgCL2. Both H-2.23 and Iak antigens present in this high density lipoprotein fraction were completely adsorbed by rabbit anit-rat beta2-microglobulin immunoadsorbents, whereas specific anti-H-2.23 immunoadsorbents removed only the H-2 activity. These data deomnstrate that Ia antigens, like H-2 antigens in the sera of B10.BR mice are associated with high density lipoproteins and further suggest that both H-2 and Ia antigens are associated with a beta2-microglobulin-like molecule.