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Functional properties of heterogeneous human asialo-C4 and its isotypes C4A and C4B. 1992

D R Schultz, and P I Arnold
Department of Medicine, University of Miami School of Medicine, Florida.

The fourth component of human complement (C4) is encoded at two separate but closely linked loci within the MHC on the short arm of chromosome 6. Thus, there are two types of C4 protein in most individual and pooled normal human sera (NHS): C4A and C4B. Incubation of individual sera, pooled NHS, or purified heterogeneous C4 (C4A/C4B) with bacterial sialidase at 37 degrees C increased C-mediated hemolysis of antibody-sensitized sheep erythrocytes 1.54- to 1.93-fold. Comparative studies of Tmax of human C2, using asialo-C4 or buffer-treated C4 on EAC1gp and extrapolation to time 0 indicated a z value 4-fold higher with asialo-C4. This indicated that more hemolytically active C42 complexes are available with sialidase-treated C4 compared to untreated C4. There was no appreciable difference in the % 125I-C4 bound to EAC1gp (sialidase- or buffer-treated). Sera from two different blood donors with C4A3 phenotype (C4BQ0), two different donors with C4B1 phenotype (C4AQ0), and serum from an individual heterozygous deficient at both C4A3 and C4B1 regions (A3, AQ0; B1, BQ0) were investigated. The C4 allotypes, purified from these sera, were treated with sialidase; the C4A3 was enhanced in hemolytic assays by sialidase-treatment (1.52- to 2.3-fold), whereas the C4B1 allotype was not enhanced. Fluorometric determinations revealed that approximately the same percentage of sialic acid was released from sialidase-treated C4A3 and C4B1. Therefore, the increase in hemolytic titer observed after treatment of NHS or purified heterogeneous C4 with sialidase is a property of C4A3 but not a property of C4B1.

UI MeSH Term Description Entries
D009439 Neuraminidase An enzyme that catalyzes the hydrolysis of alpha-2,3, alpha-2,6-, and alpha-2,8-glycosidic linkages (at a decreasing rate, respectively) of terminal sialic residues in oligosaccharides, glycoproteins, glycolipids, colominic acid, and synthetic substrate. (From Enzyme Nomenclature, 1992) Sialidase,Exo-alpha-Sialidase,N-Acylneuraminate Glycohydrolases,Oligosaccharide Sialidase,Exo alpha Sialidase,Glycohydrolases, N-Acylneuraminate,N Acylneuraminate Glycohydrolases,Sialidase, Oligosaccharide
D002021 Buffers A chemical system that functions to control the levels of specific ions in solution. When the level of hydrogen ion in solution is controlled the system is called a pH buffer. Buffer
D003175 Complement C2 A component of the CLASSICAL COMPLEMENT PATHWAY. C2 is cleaved by activated COMPLEMENT C1S into COMPLEMENT C2B and COMPLEMENT C2A. C2a, the COOH-terminal fragment containing a SERINE PROTEASE, combines with COMPLEMENT C4B to form C4b2a (CLASSICAL PATHWAY C3 CONVERTASE) and subsequent C4b2a3b (CLASSICAL PATHWAY C5 CONVERTASE). C2 Complement,Complement 2,Complement Component 2,C2, Complement,Complement, C2,Component 2, Complement
D003181 Complement C4 A glycoprotein that is important in the activation of CLASSICAL COMPLEMENT PATHWAY. C4 is cleaved by the activated COMPLEMENT C1S into COMPLEMENT C4A and COMPLEMENT C4B. C4 Complement,C4 Complement Component,Complement 4,Complement C4, Precursor,Complement Component 4,Pro-C4,Pro-complement 4,C4, Complement,Complement Component, C4,Complement, C4,Component 4, Complement,Component, C4 Complement,Pro C4,Pro complement 4
D004306 Dose-Response Relationship, Immunologic A specific immune response elicited by a specific dose of an immunologically active substance or cell in an organism, tissue, or cell. Immunologic Dose-Response Relationship,Relationship, Immunologic Dose-Response,Dose Response Relationship, Immunologic,Dose-Response Relationships, Immunologic,Immunologic Dose Response Relationship,Immunologic Dose-Response Relationships,Relationship, Immunologic Dose Response,Relationships, Immunologic Dose-Response
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D001212 Asialoglycoproteins Endogenous glycoproteins from which SIALIC ACID has been removed by the action of sialidases. They bind tightly to the ASIALOGLYCOPROTEIN RECEPTOR which is located on hepatocyte plasma membranes. After internalization by adsorptive ENDOCYTOSIS they are delivered to LYSOSOMES for degradation. Therefore receptor-mediated clearance of asialoglycoproteins is an important aspect of the turnover of plasma glycoproteins. They are elevated in serum of patients with HEPATIC CIRRHOSIS or HEPATITIS. Asialoglycoprotein,Desialylated Glycoproteins,Glycoproteins, Desialylated
D015934 Complement C4a The smaller fragment formed when complement C4 is cleaved by COMPLEMENT C1S. It is an anaphylatoxin that causes symptoms of immediate hypersensitivity (HYPERSENSITIVITY, IMMEDIATE) but its activity is weaker than that of COMPLEMENT C3A or COMPLEMENT C5A. C4a Complement,Complement 4a,Complement Component 4a,C4a, Complement,Complement, C4a,Component 4a, Complement
D015935 Complement C4b The large fragment formed when COMPLEMENT C4 is cleaved by COMPLEMENT C1S. The membrane-bound C4b binds COMPLEMENT C2A, a SERINE PROTEASE, to form C4b2a (CLASSICAL PATHWAY C3 CONVERTASE) and subsequent C4b2a3b (CLASSICAL PATHWAY C5 CONVERTASE). C4b Complement,Complement 4b,Complement Component 4b,C4b, Complement,Complement, C4b,Component 4b, Complement

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