Reference Typing Report for Complement Component C4

Abstract

During the 7th Complement Genetics Workshop, Mainz, Germany, May 1998, a complement component C4 typing exercise took place with the aim of applying present technologies to the definition of reference C4 alleles/phenotypes and the recognition of nonexpressed (Q0) C4 alleles within expressed haplotypes. Eleven samples were submitted from 3 laboratories and tested by 14 participating laboratories with basic protein-typing technologies; in addition, each laboratory contributed data from local expertise. The samples were introduced to the reference typing for one or more characteristic allotype or for partial or total nonexpression of one isotype. The blinded samples were centrally evaluated and the results discussed among the participants at a plenum meeting. From the results, the samples could be classified into a group of common, easy to diagnose pheno-/allotypes, less common but still unanimously recognised variants, and a third group with difficult pheno-/allotypes. Within the latter group, the allotypes were either new (C4A ‘92’; C4B ‘93’) and/or showed partial or total reversed antigenicity and unusual Rodgers/Chido (Rg/Ch) PCR subtypes (C4A ‘92’; C4A 12; C4B ‘35’; C4B ‘13’). Semiquantitative C4-α-chain estimates of relative isotype levels correlated well with the number of alleles seen at each locus by agarose gel electrophoresis, and were superior to other isotype quantitation methods. From the evaluation of the reference typing it was concluded that the recognition of rare, aberrant or hybrid C4 alleles with partial or total reversed Rg/Ch antigenicity or monoclonal reactivity is still difficult in most instances; besides isotype-dependent lysis, relative migration values, immunoblots with Rg- and Ch-specific monoclonal antibodies, Rg/Ch PCR typing, side-by-side comparison with already described allotypes will ultimately be required. The recognition of nonexpressed alleles within C4A and C4B expressed phenotypes remains the major obstacle in C4 genetic typing. Finally, a conclusive interpretation of DNA typing results will be achieved only in the context of complete allotyping results at the protein level, and at present cannot replace conventional protein allotyping.

Sensitive and Specific Real-Time Polymerase Chain Reaction Assays to Accurately Determine Copy Number Variations (CNVs) of Human Complement C4A, C4B, C4-Long, C4-Short, and RCCX Modules: Elucidation of C4 CNVs in 50 Consanguineous Subjects with Defined HLA Genotypes

“…The results illustrate CNV as a mechanism for generating the genetic diversity of an important immune effector protein. As we and others had shown previously, the phenotypic outcome for the sophisticated genotypic diversity of complement C4 is a wide range of plasma or serum C4 proteins among different subjects and two isotypes (C4A and C4B) with multiple protein variants (allotypes) that can have different physiologic functions (8,14,19,(55)(56)(57)(58)(59)(60).…”

Defining Targets for Complement Components C4b and C3b on the Pathogenic Neisseriae

“…Individuals generally have between two and eight C4 genes (diploid chromosome), with each locus encoding either a C4A or C4B molecule (5,79). In addition more than 41 C4 variants can be detected by differences in electrophoretic mobility (42). Partial C4 isoform deficiencies are relatively common, with the prevalence of complete C4A or C4B VOL.…”

Diversity in Intrinsic Strengths of the Human Complement System: Serum C4 Protein Concentrations Correlate withC4Gene Size and Polygenic Variations, Hemolytic Activities, and Body Mass Index

“…Human complement component C4 represents a new paradigm of complex, inborn immune diversity (3). Phenotypically, there are acidic C4A and basic C4B proteins with multiple polymorphic variants in each class (4). The plasma or serum protein levels of total C4 vary between 100 and 1000 mg/L among different individuals, as do the relative quantities of C4A and C4B proteins.…”