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Rheumatoid arthritis susceptibility and interleukin 10: a study of two ethnically diverse populations.

INTRODUCTION
IL-10 is an immunoregulatory cytokine which may modulate disease expression in rheumatoid arthritis (RA). The IL-10 gene is highly polymorphic with a number of single nucleotide polymorphisms in the promoter region and two microsatellite loci, IL10.R and IL10.G, 4 kb and 1.1 kb 5' of the transcription initiation site. It has been reported that allele 2 of the IL10.R microsatellite (IL10.R2) is associated with increased IL-10 secretion and IL10.R3 with reduced secretion. Subsequently, over-representation of IL10.R2 and under-representation of IL10.R3 in three independent RA groups has been reported. The aim of the current study is to determine whether there is an association between the IL10.R2 allele and RA in two ethnically distinct populations.


METHODS
IL10.R genotypes were determined by semi-automated DNA sequencing technology in 186 UK Caucasians and 138 South Africans of Zulu or Sotho origin, fulfilling the 1987 American College of Rheumatology (ACR) criteria for RA. The Caucasian patients had relatively severe disease and comprised 75 patients with RA vasculitis, 22 with Felty's syndrome and 89 who had undergone a joint replacement (hip or knee) within 15 years of the onset of disease. Allele frequencies were compared with 296 Caucasians and/or 73 South Africans.


RESULTS
The frequency of the IL10.R2 allele was significantly greater in the South Africans (RA and controls) than in the Caucasians (0.78 vs 0.66, P=1 x 10(-6)), while the frequency of IL10.R3 was less common (0.16 vs 0.3, P=1 x 10(-8)). No differences were observed in either IL10.R2 or IL10.R3 frequencies between patients and controls in either population.


CONCLUSIONS
We were unable to confirm any association between IL10.R alleles and RA in this study. However, significant differences were demonstrated in the frequency of IL10.R2 and IL10.R3 between the two ethnic groups. The relatively high frequency of IL10.R2 in the South African population (0.78) would have reduced the power to detect an association with RA.