REQUIREMENT FOR PROTEIN-SYNTHESIS IN ANTIGEN-PROCESSING BY B-CELLS

The role de novo protein synthesis plays in Ag processing by B cells w as investigated. Cycloheximide (CHX) inhibited Ag processing in normal and transformed B cells. B lymphoblastoid cells required a 2-6 hr lon ger CHX pretreatment period than splenic B cells to inhibit Ag process ing function. Immunoprecipitation experiments demonstrated that the ha lf-life of class II/invariant chain (Ii) complexes was similar in norm al and transformed B cells. B lymphoblastoid cells differed from splen ic B cells in that a significant fraction of total class II-associated p31 Ii was modified with sialic acid (Ip). The kinetics of loss of cl ass II-associated Ip in CHX-treated cells correlated with loss of Ag p rocessing function. In addition, the half-life of a subpopulation of c lass II molecules that are unstable in sodium dodecyl sulfate at room temperature was greater in transformed cells. Our results suggest that B lymphoblastoid cells, but not splenic B cells, contain a long-lived pool of class II/Ii complexes that can bind and present peptides gene rated in endosomal compartments for a significant time period after ce ssation of protein synthesis. (C) 1994 Academic Press, Inc.