C4 Reference Typing Report

Abstract

Human C4 is most polymorphic at the protein level, distinction between allotypes of the C4A and C4B proteins resting on electrophoretic migration patterns and difference in hemolytic activity. The aim of the C4 reference typing has been the definition of reference variants, the assignment of rare variants, and the investigation of duplicated, deleted, or non-expressed and hybrid genes. Samples from 136 individuals, predominantly with known segregation, from 16 laboratories were investigated by standard electrophoretic techniques, for their relative hemolytic activity, reactivity with monoclonal antibodies and Rg/Ch reagents, a-, and ß-chain types, relative electrophoretic migration distance, as well as the C4/21-OH-TaqI RFLPs. The results were evaluated in three groups; they consisted in the definition of the eight most common C4 alleles, and the ten Rg/Ch standard phenotypes in group I. In group II twelve C4A and fourteen C4B duplications among 96 complotypes, as well as eighteen deleted/non-expressed C4A and twenty-two C4B alleles, and hybrid alleles were seen by correlation of lytic activity, electrophoretic mobility, and monoclonal and/or Rg/Ch reactivity. Group III consisted of the newly defined allotypes A 8, A 7, A 58, A 55, A 45, B 45, B 35, and B 22, furthermore of alleles subdividing the A 1/A 91, and the B 13/ B 12/B 11 regions. The reference typing has allowed reclassification of the majority of described C4 allotypes and resulted in a revision of the C4 nomenclature.

Genetic basis of human complement C4A deficiency. Detection of a point mutation leading to nonexpression.

“…12 individuals with homozygous C4A deficiency were selected. All individuals had been haplotyped for MHC class I, II, and III gene products in family studies by our laboratory as well as by other collaborating laboratories (6,15,16) according to the following methods: HLA-A, -B, and -C, and -DR antigens were assigned by the microlymphocytotoxicity assay ( 17); C4 typing was carried out by high voltage agarose gel electrophoresis in a discontinuous buffer system after desialation ofthe samples with neuraminidase, followed by immunofixation or hemolytic overlay (18); C4QO alleles were confirmed by C4 a-chain typing using SDS-PAGE (19); restriction fragment length polymorphism analysis was carried out by Southern blot with TaqI-digested genomic DNA and hybridization to C4-and CYP2 1-specific probes as described ( 14). (15).…”

“…At the protein level C4 is highly polymorphic, with > 40 variants including null alleles (C4QO) at both loci (6). Null alleles are defined by the absence of C4 protein in plasma and are present in the normal population at frequencies of 0.1-0.3 (7).…”

Modular Variations of the Human Major Histocompatibility Complex Class III Genes for Serine/Threonine Kinase RP, Complement Component C4, Steroid 21-Hydroxylase CYP21, and Tenascin TNX (the RCCX Module)

“…More than 10 structural genes with important functions have been discovered between DR and RCCX (37). 2 Recombinant chromosomes with the essential structural genes deleted would be lethal. Therefore, the apparent productive recombination frequencies between certain MHC haplotypes would be less than expected.…”

“…1). More than 34 allotypes for C4A and C4B have been demonstrated by agarose gel electrophoresis, based on gross differences in electric charge (2). Similar to the protein, the complement C4 genes are unusually complex with frequent variations in gene size and gene number.…”

“…The TNXB gene is 68.2 kb in size, consists of 45 exons and encodes a protein of 4289 amino acids (38). 2 The derived amino acid sequence of TNXB reveals a heptad, 18.5 epidermal growth factor repeats, 32 fibronectin type III repeats, and a fibrinogen domain. The overall structure of TNXB shows a striking similarity to extracellular matrix proteins tenascin/cytostatin (TN-C) and restrictin (TN-R) (39 -41).…”