title: Difference in the clustering of complement receptor type 1 (CR1) on polymorphonuclear leukocytes and erythrocytes: effect on immune adherence.
abstract: Complement receptor type 1 (CR1) mediates the adherence of complement-reacted immune complexes (IC) to various blood cells. On the erythrocyte, CR1 are clustered, a distribution which favors efficient multivalent binding of C3b-coated IC. IC can also bind to CR1 expressed on polymorphonuclear (PMN) leukocytes. To evaluate the respective importance of these two cell types in immune adherence reactions, functional analysis of IC binding, as well as morphological studies of CR1 distribution at their surface were undertaken. At equal cell concentrations, resting PMN leukocytes bound the same percentage of IC as erythrocytes, despite expressing four times more CR1 at their surface. At equal CR1 concentrations, IC binding to resting or formyl-methionyl-leucyl-phenylalanine (fMLP)-stimulated PMN leukocytes was always lower than to erythrocytes. The morphological counterpart of these differences was studied by label-fracture immunoelectron microscopy. On erythrocytes, almost 50% of the CR1 were distributed in clusters of greater than or equal to 3 units, while less than 15% were grouped in such clusters on the surface of PMN leukocytes. Activation of PMN leukocytes by fMLP increased the surface density of CR1, but the proportion of clustered CR1 remained unchanged. These observations suggest that the low responsiveness of PMN leukocytes towards C3b-coated IC may be due to the unaggregated state of CR1. In the circulation, erythrocytes might function as a "buffer" for PMN leukocytes, which would otherwise engage too swiftly in reactions with IC.
authors: Department of Medicine, Centre Médical Universitaire, Geneva, Switzerland.
authors: J P
authors: JP
authors: Paccaud
authors: J L
authors: JL
authors: Carpentier
authors: J A
authors: JA
authors: Schifferli
mesh_terms: D000936:Antigen-Antibody Complex / Q000378:metabolism*; D000943:Antigens, Differentiation / Q000378:metabolism; D002462:Cell Membrane / Q000648:ultrastructure; D003176:Complement C3 / Q000378:metabolism; D004912:Erythrocytes / Q000276:immunology* / Q000648:ultrastructure; D005614:Freeze Fracturing; D006801:Humans; D007158:Immunologic Techniques; D066298:In Vitro Techniques; D008854:Microscopy, Electron; D009504:Neutrophils / Q000276:immunology* / Q000648:ultrastructure; D009895:Opsonin Proteins; D011940:Receptor Aggregation; D011951:Receptors, Complement / Q000378:metabolism*; D017463:Receptors, Complement 3b; D011961:Receptors, Fc / Q000378:metabolism; D017452:Receptors, IgG
chemical_list: D000936:Antigen-Antibody Complex; D000943:Antigens, Differentiation; D003176:Complement C3; D009895:Opsonin Proteins; D011951:Receptors, Complement; D017463:Receptors, Complement 3b; D011961:Receptors, Fc; D017452:Receptors, IgG