Detection of a serum class I molecule in rat with anti-rat liver beta-2-microglobulin

Rat serum was fractionated on a column of Sephacryl-300 and tested with a rabbit anti-rat beta-2-microglobulin (B2m) antiserum. This antiserum was directed against B2m purified from rat liver, and its specificity was confirmed by immunoprecipitation procedures. The antiserum recognized three peaks in the fractionated rat serum: a 200- to 300-kd (kilodalton) fraction, a 40- to 70-kd component, and the free 12-kd B2m. Indirect immunoprecipitation from the 200- to 300-kd fraction led to the identification of a 43-kd polypeptide associated with B2m. A xenoantiserum against RT1 class I antigen also precipitated a similar polypeptide from the same fraction, but this molecule differed in size and antigenic specificity from the one precipitated by anti-rat B2m.