Molecular mechanisms of soluble HLA-release by a membrane-bound metalloproteinase (MPase) are not defined. We have investigated the possibility that certain β2-microglobulin (β2m)-free heavy chains (HC) retain peptide-induced conformations before and after the cleavage by using mutant HLA-A2.242K HC with reduced affinity for β2m. We show that dissociation of HC/β2m complexes on the surface of C1R lymphoblastoid cells generates both conformed and non-conformed β2m-free HC recognized by conformation-dependent antibodies. Conformed HC, having bound the HLA-A2- specific peptide HTLV-1 tax 11-19, can retain their proper conformations after dissociation of β2m. Further, conformed and non-conformed surface β2m-free HC are cleaved by the MPase, and some released HC preserve their conformations. Exogenous β2m 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 β2m-free HC intermediates on the cell surface, which are then cleaved by the MPase and in solution may reassociate with β2m. Given the role of soluble HLA in the indirect allorecognition, the activity of this MPase may be important in transplant rejection.
All Science Journal Classification (ASJC) codes
- Immunology and Allergy
- Soluble HLA