Peptide-conformed β2m-free class I heavy chains are intermediates in generation of soluble HLA by the membrane-bound metalloproteinase

Molecular mechanisms of soluble HLA-release by a membrane-bound metalloproteinase (MPase) are nor defined, We have investigated the possibility that certain beta(2),-microglobulin (beta(2)m)-free heavy chains (HC) retain peptide-induced conformations before and after the cleavage by using mutant HLA-A2.242K HC with reduced affinity for beta(2)m We show that dissociation of HC/beta(2)m complexes on the surface of C1R lymphoblastoid cells generates both conformed and non-conformed beta(2)m-free HC recognized by conformation-dependent antibodies. Conformed HC, having bound the HLA-AZ-specific peptide HTLV-1 tax 11-19, can retain their proper conformations after dissociation of beta(2)m Further, conformed and non-conformed surface beta(2)m-free HC are cleaved by the MPase, and some released HC preserve their conformations, Exogenous beta(2)m binds only to conformed HC, and protects them from cleavage as effectively as the MPase inhibitor BB-2116. We propose that soluble HLA-release requires generation of peptide-conformed beta(2)m-free HC intermediates on the cell surface, which are then cleaved by the MPase and in solution map reassociate with beta(2)m. Given the role of soluble HLA in the indirect allorecognition, the activity of this MPase may be important in transplant rejection. (C) American Society for Histocompatibility and Immunogenetics, 1999. Published by Elsevier Science Inc.