THE SPECIFICITY AND EFFICIENCY OF ENDOGENOUS PEPTIDES IN THE INDUCTION OF HLA CLASS-I ALPHA-CHAIN REFOLDING

The specificity and efficiency of endogenous peptides in the HLA class I binding have been investigated by the use of a simple procedure that is based on the serological detection of the folding of HLA class I alpha-chains that is induced by the binding to specific peptides in the presence of beta-2 microglobulin. HLA class I proteins were solubilized with a nonionic detergent from cultured HLA homozygous B lymphoblastoid cells and dissociated by alkaline denaturation. The resulting unfolded alpha-chains were isolated by gel filtration at a neutral pH. The unfolded alpha-chains showed a high refolding capacity and specificity when tested in the presence of an excess beta-2 microglobulin against endogenous peptides extracted by alkaline or acid treatment from cultured B lymphoblastoid cells of various HLA class I phenotypes. Cells of identical or overlapping HLA phenotypes clearly showed shared peptides, whereas such peptide sharing was rarely, if at all, seen between cells of non-overlapping HLA phenotypes. The efficiency of endogenous peptides in the induction of refolding was high; at an estimated concentration of 0.2-mu-m or less, a strong refolding effect was observed.