title: Receptor-mediated antigen delivery into macrophages. Complexing antigen to alpha 2-macroglobulin enhances presentation to T cells.
abstract: Macrophages secrete alpha 2-macroglobulin (alpha 2M), a protein that may facilitate early Ag handling. alpha 2M is able to entrap and form covalent linkages with diverse proteins during a transient proteinase-activated state. The resulting complexes are rapidly endocytosed after binding to high affinity receptors. Such a system could be capable of efficiently delivering a multitude of proteins to macrophages. We have used T hybridoma clones that respond only to hen egg lysozyme, in a MHC-restricted manner, to probe the effect of complex formation on Ag uptake and processing by murine macrophages. Radiolabeled lysozyme was internalized more rapidly and to a greater extent when bound to alpha 2M than when unbound. Macrophages pulsed with lysozyme-alpha 2M-elastase complexes required 200 to 250 times less Ag than those pulsed with free lysozyme to achieve effective presentation to T cells. Adding equimolar amounts of alpha 2M-elastase complexes, or of alpha 2M-methylamine, to free lysozyme had no effect on basal lysozyme presentation. Receptor-recognized forms of alpha 2M, but not lysozyme or BSA, competed effectively for both uptake and presentation of lysozyme-alpha 2M-elastase complexes. These results indicate that proteinase-activated alpha 2M can enhance Ag processing by carrying Ag into macrophages through a receptor-mediated process.
authors.affiliation: Department of Pathology, Duke University Medical Center, Durham, NC 27710.
authors.forename: C T
authors.initials: CT
authors.lastname: Chu
authors.forename: S V
authors.initials: SV
authors.lastname: Pizzo
mesh_terms: D000818:Animals; D000938:Antigen-Presenting Cells / Q000378:metabolism*; D005260:Female; D006825:Hybridomas / Q000276:immunology / Q000378:metabolism; D008264:Macrophages / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D008808:Mice, Inbred CBA; D009113:Muramidase / Q000276:immunology / Q000378:metabolism; D011485:Protein Binding / Q000276:immunology; D011946:Receptors, Antigen / Q000378:metabolism*; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism*; D000511:alpha-Macroglobulins / Q000276:immunology / Q000378:metabolism*
chemical_list: D011946:Receptors, Antigen; D000511:alpha-Macroglobulins; D009113:Muramidase