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Molecular Analysis of Complement Component C4 Gene Copy Number

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Immunogenetics

Part of the book series: Methods in Molecular Biology ((MIMB,volume 882))

Abstract

Classical, alternative, or lectin pathways may activate the complement system cascade. The classical pathway includes the C4 protein and functions in the prevention of immune complex precipitation and in clearance of immune complexes.

Two isotypes of C4—C4A and C4B—are coded by genes located at two loci within the major histocompatibility complex (MHC) on chromosome 6. While these isotypes share over 99% amino acid sequence homology, five nucleotide differences located in exon 26 are responsible for major structural and functional differences between the C4 isotypes.

C4A and C4B are highly polymorphic with over 40 alleles, gene duplications, and “null alleles”. C4 genes may be short (14.6 kb) or long (21 kb), due to the absence or presence of an endogenous retroviral sequence—HERV-K(C4)—in intron 9, respectively. The C4 gene copy number (GCN) can vary from 1–3 per haplotype or 2–6 per diploid genome. The variation in GCN leads to a range of C4 plasma protein concentrations among healthy subjects. In subjects with equal numbers of C4 genes, subjects with short genes have C4 plasma levels relatively higher than subjects with long genes.

Variation of the C4 GCN, the gene size (long or short) and the C4 isotypes (C4A and C4B) may also lead to susceptibility to autoimmune disease. Therefore, in subjects with autoimmune disease, a low serum C4 level may be due to ongoing disease activity associated with complement activation and consumption or it may be due to genetic factors. Distinguishing between these will have clinical implications.

Exact determination of GCN can be difficult, at least in part due to the high degree of homology between C4A and C4B and a variety of techniques has been described. This chapter describes a quantitative TaqMan real-time PCR (qPCR) copy number assay, based on our laboratory experience using this assay.

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Author information

Authors and Affiliations

  1. Department of Clinical Immunology, PathWest Laboratory Medicine, Royal Perth Hospital, Perth, WA, Australia

    Alison S. L. Castley

  2. Department of Clinical Immunology, PathWest Laboratory Medicine, Royal Perth and Fremantle Hospitals, Perth, WA, Australia

    O. Patricia Martinez

  3. School of Pathology and Laboratory Medicine (PaLM), University of Western Australia, Nedlands, WA, Australia

    O. Patricia Martinez

Authors
  1. Alison S. L. Castley
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  2. O. Patricia Martinez
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Corresponding author

Correspondence to O. Patricia Martinez .

Editor information

Editors and Affiliations

  1. PathWest Laboratory Medicine, Department of Clinical Immunology, Royal Perth Hospital, Wellington Street, Perth, 6000, Australia

    Frank T. Christiansen

  2. Australian Red Cross Blood Service, National Transplant Services, The Royal Melbourne Hospital, 150-154 Batman Street, Melbourne VIC, 3000, Australia

    Brian D. Tait

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Castley, A.S.L., Martinez, O.P. (2012). Molecular Analysis of Complement Component C4 Gene Copy Number. In: Christiansen, F., Tait, B. (eds) Immunogenetics. Methods in Molecular Biology, vol 882. Humana Press, Totowa, NJ. https://doi.org/10.1007/978-1-61779-842-9_9

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  • DOI: https://doi.org/10.1007/978-1-61779-842-9_9

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  • Publisher Name: Humana Press, Totowa, NJ

  • Print ISBN: 978-1-61779-841-2

  • Online ISBN: 978-1-61779-842-9

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