Complement - Factor H / Factor I

Immunology

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Description

Factor H is a 150kD glycoprotein which circulates in the human plasma. It plays a central regulatory role within the alternative complement pathway acting to inhibit the assembly and activation of C3 convertase. The presence of factor H is a prerequisite in the blocking of spontanious activation of the alternative pathway. In the absence of factor H there is continous activation of the alternative pathway, depletion of C3 and an increase in the terminal membrane attack complex (MAC) [1]. Factor I deficiency also leads to continous activation of the alternative pathway and depletion of C3 [3]. The critical role of factor H defects in the development of MPGN type II is shown by the fact that C3 depletion does not cause MPGN type II. Homozygous factor H deficiency and factor I deficiency are associated with the recurrent haemolytic-uraemic syndrome (HUS) [1,4]. Factor H deficiency has also been associated with the retinal condition, age-related macular degeneration [2].

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Indications

Factor H deficiency has been associated with the hypocomplementaemia and glomerular C3 deposition seen in membranoproliferative glomerulonephritis (MPGN type II). Hemolytic uremic syndrome (HUS) and Age-related macular degeneration (ARMD).

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Sample Type

2mL Serum (5mL red tube). Separate from the blood clot within 6 hours of venesection.
Requests from outside Sheffield: transport at ambient temperature via Royal Mail or Courier.

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Reference Range

Factor H: 345 - 590 mg/L. Factor I: 38 - 58 mg/L. Manufacturer derived.

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Turnaround Time

Within 2 weeks

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Testing Frequency

As required (send away test)

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References

PRU Handbook of Clinical Immunochemistry. 9th Edition. 2007. [Ref 1]
Jozsi M and Zipfel PF. Factor H family proteins and human diseases. Trends in Imm. 2008. 29:380-387. [Ref 2]
Tsiftsoglou SA, et al. Human complement factor I glycosylation: Structural and functional characterisation of the N-linked oligosaccharides. Biochem Biophys acta - Proteins and proteomics. 2006. 764(11):1757-1766. [Ref 3]
Noris M and Remuzzi G. Hemolytic uremic syndrome, J. Am. Soc. Nephrol. 2005. 16:1035-1050. [Ref 4].

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See Also

C3
AP50
CH50
C3NEF
C3d

Please note: the above information is subject to change and we endeavour to keep this website up to date wherever necessary.