title: Polymorphism of the complement components in human pathology.
abstract: The complement system is an important part of non clonal or innate immunity that collaborates with acquired immunity to kill pathogens and to facilitate the clearance of immune complexes. The complement is made up of 20 distinct plasma proteins and 9 different membrane proteins. Three components, factor B, C2 and C4 (with 2 isotypes), are coded by polymorphic HLA-linked genes and are sometimes referred to as class III antigens, inherited as compact units called complotypes. The C4 genes are the most polymorphic, including a common null allele (Q0) at both the C4A and C4B loci. Other polymorphic complement factors (not linked to HLA) are C3 (2 common alleles), C6 and C7 (closely linked, with 3 and 2 alleles, respectively). A certain degree of polymorphism has also been described for complement receptors and membrane control proteins. No differences in functional activity are usually detected among different alleles. Immune-mediated diseases are associated with C4Q0, in particular: systemic lupus erythematosus and discoid-systemic lupus erythematosus, insulin-dependent diabetes mellitus, liver cirrhosis, celiac disease and IgA/IgG4 deficiency. Even if optimal HLA markers do become available, genetic counselling is usually not the ultimate goal for dealing with most of the HLA-associated common diseases, although their study could help to better delineate disease pathogenesis.
authors.affiliation: Cattedra di Immunologia, Università degli Studi di Palermo.
authors.forename: M
authors.initials: M
authors.lastname: Brai
authors.forename: P
authors.initials: P
authors.lastname: Accardo
authors.forename: D
authors.initials: D
authors.lastname: Bellavia
mesh_terms: D000312:Adrenal Hyperplasia, Congenital / Q000235:genetics / Q000276:immunology; D000368:Aged; D000369:Aged, 80 and over; D000483:Alleles; D002648:Child; D003175:Complement C2 / Q000172:deficiency; D003176:Complement C3 / Q000235:genetics; D003181:Complement C4 / Q000235:genetics; D003165:Complement System Proteins / Q000235:genetics*; D003922:Diabetes Mellitus, Type 1 / Q000235:genetics / Q000276:immunology; D005260:Female; D008040:Genetic Linkage; D005819:Genetic Markers; D006801:Humans; D017098:IgA Deficiency / Q000235:genetics; D017099:IgG Deficiency / Q000235:genetics; D008180:Lupus Erythematosus, Systemic / Q000235:genetics / Q000276:immunology; D008285:Major Histocompatibility Complex / Q000235:genetics / Q000276:immunology; D008297:Male; D008875:Middle Aged; D011110:Polymorphism, Genetic; D011951:Receptors, Complement / Q000235:genetics
chemical_list: D003175:Complement C2; D003176:Complement C3; D003181:Complement C4; D005819:Genetic Markers; D011951:Receptors, Complement; D003165:Complement System Proteins