Biochemical and immunologic heterogeneity of Ia glycoproteins isolated from a chronic lymphocytic leukemia

Ia glycoproteins have been isolated from human chronic lymphocytic leukemic cells (CLL) by Lens culinaris chromatography and by filtration on ACA-34 Ultrogel. Ia antigenic activity, measured by inhibition of the cellular radioimmunoassay, was separated by gel filtration into 2 fractions, peak I and peak II. Monoclonal antibodies, produced against peak II glycoproteins, appear to recognize different antigenic determinants of Ia molecules. Monoclonal antibody 18a4 reacted with Ia molecules of peaks I and II, whereas monoclonal antibodies 18c2 and 18d5 reacted almost exclusively with peak II molecules both in the cellular radioimmunoassay and by immunoprecipitation. In addition to antigenic differences, minor variations in the apparent m.w. of the Ia polypeptide chains were observed between peaks I and II. These results indicate the existence of antigenically distinct subsets of Ia molecules that are separable by gel filtration.