title: C1q and mannose binding lectin engagement of cell surface calreticulin and CD91 initiates macropinocytosis and uptake of apoptotic cells.
abstract: Removal of apoptotic cells is essential for maintenance of tissue homeostasis, organogenesis, remodeling, development, and maintenance of the immune system, protection against neoplasia, and resolution of inflammation. The mechanisms of this removal involve recognition of the apoptotic cell surface and initiation of phagocytic uptake into a variety of cell types. Here we provide evidence that C1q and mannose binding lectin (MBL), a member of the collectin family of proteins, bind to apoptotic cells and stimulate ingestion of these by ligation on the phagocyte surface of the multifunctional protein, calreticulin (also known as the cC1qR), which in turn is bound to the endocytic receptor protein CD91, also known as the alpha-2-macroglobulin receptor. Use of these proteins provides another example of apoptotic cell clearance mediated by pattern recognition molecules of the innate immune system. Ingestion of the apoptotic cells through calreticulin/CD91 stimulation is further shown to involve the process of macropinocytosis, implicated as a primitive and relatively nonselective uptake mechanism for C1q- and MBL-enhanced engulfment of whole, intact apoptotic cells, as well as cell debris and foreign organisms to which these molecules may bind.
authors.affiliation: Department of Pediatrics, National Jewish Medical and Research Center, Denver, CO 80206, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Ogden
authors.forename: A
authors.initials: A
authors.lastname: deCathelineau
authors.forename: P R
authors.initials: PR
authors.lastname: Hoffmann
authors.forename: D
authors.initials: D
authors.lastname: Bratton
authors.forename: B
authors.initials: B
authors.lastname: Ghebrehiwet
authors.forename: V A
authors.initials: VA
authors.lastname: Fadok
authors.forename: P M
authors.initials: PM
authors.lastname: Henson
mesh_terms: D017209:Apoptosis / Q000276:immunology*; D002135:Calcium-Binding Proteins / Q000276:immunology*; D037282:Calreticulin; D002352:Carrier Proteins / Q000276:immunology*; D002478:Cells, Cultured; D003094:Collagen / Q000276:immunology; D037222:Collectins; D015922:Complement C1q / Q000276:immunology*; D006801:Humans; D019169:Jurkat Cells; D037102:Lectins / Q000276:immunology*; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008264:Macrophages / Q000276:immunology*; D009000:Monocytes / Q000166:cytology; D010587:Phagocytosis / Q000276:immunology; D010873:Pinocytosis / Q000276:immunology*; D011971:Receptors, Immunologic / Q000276:immunology*; D012261:Ribonucleoproteins / Q000276:immunology*; D015398:Signal Transduction / Q000276:immunology
chemical_list: D002135:Calcium-Binding Proteins; D037282:Calreticulin; D002352:Carrier Proteins; D037222:Collectins; D037102:Lectins; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D011971:Receptors, Immunologic; D012261:Ribonucleoproteins; D015922:Complement C1q; D003094:Collagen