This protein recognizes C4b and C3b fragments that condense with cell-surface hydroxyl or amino groups when nascent C4b and C3b are locally generated during C4 and c3 activation. Interaction of daf with cell-associated C4b and C3b polypeptides interferes with their ability to catalyze the conversion of C2 and factor B to enzymatically active C2a and Bb and thereby prevents the formation of C4b2a and C3bBb, the amplification convertases of the complement cascade.
Using an anti-receptor mAb that blocks the attachment of echovirus 7 and related viruses (echoviruses 13, 21, 29 and 33), we have isolated a complementary DNA clone that encodes the human decay-accelerating factor (CD55). Mouse cells transfected with the CD55 clone bind echovirus 7, and this binding is blocked by the anti-receptor mAb. The method used (CELICS) allows rapid and direct cloning of genes encoding cell surface receptors. It is based on episomal replication and high efficiency expression of complementary DNA clones in the vector pCDM8 in COS or WOP cells, in conjunction with a sensitive immuno-focal screen that uses antibody probes linked to beta-galactosidase. Receptor positive cells were identified by a colour change and isolated individually using a micromanipulator. DNA extracted from a small number of cells was then cloned directly in Escherichia coli.
Any process involved in the activation of any of the steps of the classical pathway of the complement cascade which allows for the direct killing of microbes, the disposal of immune complexes, and the regulation of other immune processes.
The present study investigated possible receptor-like characteristics of glycosylphosphatidylinositol (GPI)-linked antigens on human monocytes and granulocytes by measuring cytoplasmic calcium fluxes and the oxidative burst in cells following cross-linking of GPI-linked antigens. Cross-linking of cell-bound anti-CD14, -CDw52 and -CD55 induced cytoplasmic calcium fluxes and oxidative bursts in unprimed human monocytes similar to those observed following Fc gamma R cross-linking. In granulocytes primed with 200 mM N-formyl-Met-Leu-Phe (FMLP), cross-linking of cell-bound anti-CD16, -CD24, -CD59 and -CD67 led to calcium fluxes and activation of the oxidative burst. The oxidative bursts mediated by GPI-linked antigens were stronger than those induced by 200 nM FMLP, even though FMLP induced a larger increase in cytoplasmic calcium concentration. The responses were likely to be independent of Fc gamma R interactions as F(ab')2 fragments of IgG or IgM antibodies were used in the experiments. Activating effects of monoclonal antibody to GPI-linked antigens were not observed in cells from patients with paroxysmal nocturnal hemoglobinuria, which are deficient in GPI-linked antigens. In addition, treatment with GPI-specific phospholipase C led to inhibition of cell activation through GPI-linked antigens but not through transmembrane receptors. Cross-linking of a number of non-GPI-linked antigens (CD11a, CD18, CD31, CD35, CD43, and CD45) neither induced calcium fluxes, nor activated the oxidative burst. The results indicate that most, if not all, GPI-linked surface glycoproteins on myeloid cells are capable of mediating cell activation and suggest that the GPI anchor is a structure facilitating signal transduction.
A phase of elevated metabolic activity, during which oxygen consumption increases; this leads to the production, by an NADH dependent system, of hydrogen peroxide (H2O2), superoxide anions and hydroxyl radicals.
The present study investigated possible receptor-like characteristics of glycosylphosphatidylinositol (GPI)-linked antigens on human monocytes and granulocytes by measuring cytoplasmic calcium fluxes and the oxidative burst in cells following cross-linking of GPI-linked antigens. Cross-linking of cell-bound anti-CD14, -CDw52 and -CD55 induced cytoplasmic calcium fluxes and oxidative bursts in unprimed human monocytes similar to those observed following Fc gamma R cross-linking. In granulocytes primed with 200 mM N-formyl-Met-Leu-Phe (FMLP), cross-linking of cell-bound anti-CD16, -CD24, -CD59 and -CD67 led to calcium fluxes and activation of the oxidative burst. The oxidative bursts mediated by GPI-linked antigens were stronger than those induced by 200 nM FMLP, even though FMLP induced a larger increase in cytoplasmic calcium concentration. The responses were likely to be independent of Fc gamma R interactions as F(ab')2 fragments of IgG or IgM antibodies were used in the experiments. Activating effects of monoclonal antibody to GPI-linked antigens were not observed in cells from patients with paroxysmal nocturnal hemoglobinuria, which are deficient in GPI-linked antigens. In addition, treatment with GPI-specific phospholipase C led to inhibition of cell activation through GPI-linked antigens but not through transmembrane receptors. Cross-linking of a number of non-GPI-linked antigens (CD11a, CD18, CD31, CD35, CD43, and CD45) neither induced calcium fluxes, nor activated the oxidative burst. The results indicate that most, if not all, GPI-linked surface glycoproteins on myeloid cells are capable of mediating cell activation and suggest that the GPI anchor is a structure facilitating signal transduction.
Any process that results in a change in state or activity of a cell or an organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a peptide hormone stimulus. A peptide hormone is any of a class of peptides that are secreted into the blood stream and have endocrine functions in living animals.
Pathway which activates the proteins of the complement system, a group of blood proteins of the globulin class involved in the lysis of foreign cells after they have been coated with antibody, and which also promote the removal of antibody-coated foreign particles by phagocytic cells. The pathway proceeds by a cascade reaction of successive binding and proteolytic cleavage of complement components. This pathway can be activated by either IgG or IgM binding to an antigen.
Protein involved in immunity, any immune system process that functions in the response of an organism to a potential internal or invasive threat. The vertebrate immune system is formed by the innate immune system (composed of phagocytes, complement, antimicrobial peptides, etc) and by the adaptive immune system which consists of T- and B- lymphocytes.
Protein involved in innate immunity, an inborn defense mechanism used by organisms to defend themselves against invasion by pathogens (bacteria, fungi, viruses, etc.). Initially discovered in insects which are devoid of an adaptive immune system and rely only on innate immune reactions for their defense, this immediate response accomplishes many activities including recognition and effector functions. Recognition is mediated by broad specificity, pattern recognition, receptors which recognize many related molecular structures (e.g. polysaccharides, polynucleotides) present in microorganisms but not found in the host. The innate responses include the release of antimicrobial peptides, production of cytokines, acute- phase proteins, complement. Although many different innate immune mechanisms are deployed for host defence, a unifying theme of innate immunity is the use of germline-encoded pattern recognition receptors for pathogens or damaged self components, such as the Toll-like receptors, nucleotide-binding domain leucine-rich repeat (LRR)- containing receptors, retinoic acid-inducible gene I-like RNA helicases and C-type lectin receptors.
Protein belonging to the set of cell surface antigens found chiefly, but not solely, on blood cells. More than fifteen different blood group systems are recognised in humans. In most cases the antigenic determinant resides in the carbohydrate chains of membrane glycoproteins or glycolipids.
Cell surface protein used by a virus as an attachment and entry receptor. In some cases, binding to a cellular receptor is not sufficient for infection: an additional cell surface molecule, or coreceptor, is required for entry. Some viruses are able to use different receptors depending on the target cell type.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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