Association of IL-6 gene alleles with systemic lupus erythematosus (SLE) and with elevated IL-6 expression

To evaluate the association of alleles of regions having regulatory potential in the IL-6 gene, with SLE, the AT-rich minisatellite in the 3' flanking region and the 5' promoter-enhancer of the IL-6 gene were genotyped by PCR- and RFLP-based methods. The AT-rich minisatellite allele distribution pattern was significantly different in SLE (n = 146) as compared to 139 controls (chi(7)(2) = 48.97, P = 0.001, Caucasians; and chi(7)(2) =19.93, P = 0.006 African-Americans). In either race, short allele sizes less than or equal to 792 bp) were seen exclusively in SLE patients (P = 0.001), whereas the 828-bp allele was overrepresented in controls (P = 0.015 and 0.002). In contrast, there was no preferential association of SLE with G/C alleles in the 5' region of the IL-6 gene. Furthermore, our results suggest that the 3' minisatellite alleles have biological significance: (1) B lymphoblastoid cells of patients having one or two SLE-associated alleles secreted IL-6 in 3- to 4-fold higher levels than non-allelic cells (P < 0.05); (2) higher percentages (approximately 4-fold) of IL-6 positive monocytes were observed in individuals having SLE-associated IL-6 alleles; (3) in lupus patients having SLE-associated minisatellite alleles, IL-6 mRNA stability was significantly enhanced.