Decreased expression of Ii-derived p25 and of P67/69 in hairy leukemic cells.

Hairy leukemic cells had altered expressions of accessory proteins (Ii, Ip, p70, p25) which associated intracellularly with class II MHC molecules. Immunoprecipitates from [35S]methionine, pulse-chase labeled leukemic cells, B-lymphoblastoid cells, and Burkitt's lymphoma cells were examined after 2-dimensional, polyacrylamide gel electrophoresis. The class II MHC-associated Ii chain was present in all three cell types, but the Ii-derived p25 protein was not found in HCL cells. Ip, the sialic acid-derivatized form of Ii, was well expressed in BLCL and Raji cells, but weakly in HCL cells. P70 was strongly expressed in BLCL and Raji cells, but negligibly in HCL cells. These alterations might reflect deficient mechanisms for antigen processing and presentation by these leukemic cells.