Fine mapping of the MHC Class III region demonstrates association of AIF1 and rheumatoid arthritis.
OBJECTIVE
The heritability of RA has been estimated to be approximately 55%, of which the MHC contributes about one-third. HLA-DRB1 alleles are strongly associated with RA, but it is likely that significant non-DRB1 MHC genetic susceptibility factors are involved. Previously, we identified two three-marker haplotypes in a 106-kb region in the MHC class III region immediately centromeric to TNF, which are strongly associated with RA on HLA-DRB1*0404 haplotypes. In the present study, we aimed to refine these associations further using a combination of genotyping and gene expression studies.


METHODS
Thirty-nine nucleotide polymorphisms (SNPs) were genotyped in 95 DRB1*0404 carrying unrelated RA cases, 125 DRB1*0404-carrying healthy controls and 87 parent-case trio RA families in which the affected child carried HLA-DRB1*04. Quantitative RT-PCR was used to assess the expression of the positional candidate MHC class III genes APOM, BAT2, BAT3, BAT4, BAT5, AIF1, C6orf47, CSNK2beta and LY6G5C, and the housekeeper genes, hypoxanthine-guanine phosphoribosyltransferase (HPRT) and beta(2)-microglobulin (B2M) in 31 RA cases and 21 ethnically, age- and sex-matched healthy controls. Synovial membrane specimens from RA, PsA and OA cases were stained by an indirect immunoperoxidase technique using a mouse-anti-human AIF1 monoclonal antibody.


RESULTS
Association was observed between RA and single markers or two marker haplotypes involving AIF1, BAT3 and CSNK. AIF1 was also significantly overexpressed in RA mononuclear cells (1.5- to 1.9-fold difference, P = 0.02 vs HPRT, P = 0.002 vs B2M). AIF1 protein was clearly expressed by synovial macrophages in all the inflammatory synovial samples in contrast to the non-inflammatory OA samples.


CONCLUSIONS
The results of the genotyping and expression studies presented here suggest a role for AIF1 in both the aetiology and pathogenesis of RA.
Diamantina Institute of Cancer, Immunology and Metabolic Medicine, Princess Alexandra Hospital, Ipswich Road, Woolloongabba, Queensland 4102, Australia.
S M J
SM
Harney
C
C
Vilariño-Güell
I E
IE
Adamopoulos
A-M
AM
Sims
R W
RW
Lawrence
L R
LR
Cardon
J L
JL
Newton
C
C
Meisel
J J
JJ
Pointon
C
C
Darke
N
N
Athanasou
B P
BP
Wordsworth
M A
MA
Brown
D001172:Arthritis, Rheumatoid / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002135:Calcium-Binding Proteins; D016022:Case-Control Studies; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D020022:Genetic Predisposition to Disease; D005838:Genotype; D006684:HLA-DR Antigens / Q000235:genetics; D059811:HLA-DRB1 Chains; D006801:Humans; D007124:Immunoenzyme Techniques; D015810:Linkage Disequilibrium; D008285:Major Histocompatibility Complex / Q000235:genetics; D008840:Microfilament Proteins; D010003:Osteoarthritis / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D020641:Polymorphism, Single Nucleotide; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D013583:Synovial Membrane / Q000378:metabolism / Q000473:pathology
C112986:AIF1 protein, human; D002135:Calcium-Binding Proteins; D004268:DNA-Binding Proteins; D006684:HLA-DR Antigens; D059811:HLA-DRB1 Chains; D008840:Microfilament Proteins