Complement C4 is mapped to human chromosome 6p21.33. It exists in two isoforms as c4A and c4B. C4 is a 200 kDa protein belonging to α2 macroglobulin (α2M) family. It undergoes posttranslational modification like sulfation and glycosylation and finally proteolysis to become a mature protein.

Complement C4 from human serum has been used in mannose binding lectin (MBL) complex assay of serum samples and in MBL-associated serine proteases based C4 activation assay of plasma samples.

Complement C4 serves a primary role in the classical and lectin pathways of the complement system and provides protection against bacterial pathogens. C4 polymorphisms have been used in research to study their associations with the hemolytic and antibacterial ability of the classical pathway.

There are strong indications that complement C4 deficiency is correlated with induction of systemic lupus erythematosus (SLE) and other autoimmune diseases.

Variation in the copy number of the complement C4 gene alters the complement c4A and c4B levels in age-related macular degeneration (AMD) and increases risk of developing schizophrenia.

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View more information on the complement pathway at www.sigma-aldrich.com/enzymeexplorer

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