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L.V. Johnson, P.T. Johnson, M.J. Radeke, K.E. Betts, D.H. Anderson; Elevated Choroidal Levels of C–Reactive Protein in Individuals Homozygous for the AMD Risk–Conferring Polymorphism (Y402H) of Complement Factor H . Invest. Ophthalmol. Vis. Sci. 2006;47(13):865.
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© ARVO (1962-2015); The Authors (2016-present)
A T––>C substitution at nucleotide 1277 in exon 9 of the Complement Factor H gene (CFH) is associated with a significantly increased risk of AMD. Reported odds ratios for AMD are 2.4–4.6 for carriers of at least one copy of the C allele, and 3.3–7.4 for CC homozygotes. The T––>C substitution in the CFH gene results in a tyrosine ––>histidine change at position 402 (Y402H) in the CFH protein. We assessed the relationship between the risk–conferring CFH isoform (HH), the ocular distributions of CFH, CFH–binding proteins, and components of complement activation at the RPE–choroid interface.
Human donor eyes were genotyped at CFH nucleotide 1277 by PCR–based SNP analysis. RPE/choroid tissue from extramacular locations of YY and HH homozygotes were examined immunohistochemically using antibodies against CFH, terminal pathway complement components, and two CFH–binding proteins [C3b and C–reactive protein (CRP)]. Western blot analysis was conducted on extracts of RPE/choroid tissue using a similar panel of antibodies.
In individuals homozygous for the at risk (HH) or protective (YY) CFH alleles, immunoreactivity patterns for CFH, C5, and C3b were similar in the choroidal stroma, in drusen, and in other sub–RPE deposits. No significant differences in tissue distribution or staining intensity were detected at extramacular locations. CRP immunoreactivity, however, was significantly more intense in the choroidal stroma of individuals homozygous for the risk–conferring allele. When conditions were optimized for immunofluorecence detection of CRP in HH homozygotes, CRP was barely detectable in the choroids of YY individuals. Western blotting confirmed this observation, demonstrating >4–fold higher levels of CRP in RPE/choroid of those possessing the at risk CFH haplotype.
Individuals homozygous for the risk–conferring AMD allele in the CFH gene exhibit increased levels of CRP deposition within the choroid but no significant differences in the density or distribution of CFH, C5, or C3b. Since the CRP binding site of the CFH protein lies in the domain containing the Y402H polymorphism, the risk–conferring CFH allele may affect the CRP–binding properties of CFH and influence the deposition of CRP within the choroidal stroma.
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