Characterization of the murine homolog of C1qRP: identical cellular expression pattern, chromosomal location and functional activity of the human and murine C1qRP (original) (raw)
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Identification of human CD93 as the phagocytic C1q receptor (C1qRp) by expression cloning
2000
CD93 is a 120 kDa O-sialoglycopro- tein that within the hematopoietic system is selec- tively expressed on cells of the myeloid lineage. So far, its primary structure and function were un- known. We used retroviral-expression cloning to isolate the CD93 cDNA. Sequence analysis re- vealed that CD93 is identical to a protein on hu- man phagocytes termed C1q receptor (C1qRp).
The Classical and Regulatory Functions of C1q in Immunity and Autoimmunity
Cellular & Molecular Immunology, 2008
A classical function of C1q is to bind immune complexes and initiate complement activation producing membrane lytic complexes, opsonins and anaphylatoxins. This classical pathway of complement activation is also elicited when C1q binds some other ligands. Besides complement activation, C1q also regulates cell differentiation, adhesion, migration, activation and survival. C1q deficiency is associated with autoimmunity as well as increased susceptibility to infections. In this article, we discuss the basic properties of C1q, its expression, and classical and regulatory functions. Cellular & Molecular Immunology. 2008;5(1):9-21.
2001
C1qR P is a type I cell surface glycoprotein that has been shown to enhance ingestion of suboptimally opsonized targets by phagocytes in vitro. In this study, we developed and characterized polyclonal antibodies to study the tissue distribution of this receptor targeted to either the N-or C-terminal portion of the molecule. C1qR P was detected in vascular endothelial cells and in a subset of pyramidal neurons in the brain, as well as neutrophils, but it was absent in most tissue macrophages.
Human T cells express specific binding sites for C1q. Role in T cell activation and proliferation
The Journal of Immunology
Although the receptor that binds to the collagen-like domain of human C1q (C1qR) is expressed on a wide variety of cell types, the presence or absence of this receptor on human T lymphocytes has been debatable. The current studies were undertaken to re-examine whether human T cells possess specific binding sites for C1q by using a combination of techniques, including radioligand binding studies, flow cytometric analysis, and epifluorescence imaging techniques. Radioligand binding studies indicate that both peripheral T cells and the cultured T cell line, MOLT4, bind 125I-labeled C1q in a specific and apparently saturable manner, reaching equilibrium within 30 min at 37 degrees C under conditions of subphysiologic (90 mM NaCl) ionic strength. Western blot analysis with anti-C1qR of membrane proteins derived from Raji and MOLT4 cells showed an apparent single band of approximately 60 kDa under nonreducing conditions. Furthermore, when peripheral blood T cells were stimulated with 12,-...
New insight into the autoimmunogenicity of the complement protein C1q
Molecular Immunology, 2011
C1q along with its physiological role in maintenance of homeostasis and normal function of the immune system is involved in pathological conditions associated with repetitive generation of anti-C1q autoantibodies. The time and events that cause their first appearance are still unknown. We addressed this issue by analyzing the immunogenicity of C1q in two target groups-one of non-diseased humans and the other of lupus nephritis (LN) patients whose autoimmune disorder is associated with high titers of anti-C1q autoantibodies. The non-diseased humans were represented by pregnant women because the sex hormones are thought to be involved in triggering autoimmune pathologies by their ability to tip the balance of female adaptive immune response to production of antibodies.
The Journal of experimental medicine, 1984
We have shown previously that an activity which is capable of precipitating purified C1q and inhibiting some of the C1q-dependent biologic reactions could be solubilized from the membranes of both normal human peripheral B lymphocytes and a B cell-derived lymphoblastoid cell line (Raji), both of which are known to possess receptors for human C1q. In this report we present evidence that this membrane-associated C1q inhibitor is a chondroitinase-insensitive macromolecule and is the receptor for human C1q. The receptor was solubilized from membranes of Raji cells with Nonidet P-40 and purified to homogeneity using C1q-Sepharose 4B affinity chromatography. Equilibrium density gradient centrifugation analysis revealed that the complex could be resolved into a protein-rich, low density fraction and a carbohydrate-rich, high density fraction. The large hydrodynamic size, coupled with the high buoyant density, suggests that a proteoglycan is a constituent of the complex and indicates that t...