Interleukin 10 secretion in relation to human IL-10 locus haplotypes

Abstract

Stimulation of human blood cultures with bacterial lipopolysaccharide (LPS) shows large inter-individual variation in interleukin 10 (IL-10) secretion, which has been shown to have a genetic component of over 70%. Alleles at two microsatellite loci in the 4 kb immediately upstream of the human IL-10 transcription initiation site in 132 individuals from 56 Dutch families were defined and assigned as haplotypes. LPS-induced IL-10 secretion was measured by ELISA and related to the IL-10 promoter haplotypes present in 78 unrelated individuals obtained from these families. Analysis showed that LPS-induced IL-10 secretion from unrelated individuals varied with IL-10 promoter haplotypes (P = 0.024; Kruskal-Wallis test). Two observations were made in relation to secreted IL-10 levels and promoter haplotypes; first, those haplotypes containing the allele IL10.R3 were associated with lower IL-10 secretion than haplotypes containing any other IL10.R allele. Second, the haplotype IL10.R2/IL10.G14 was associated with highest IL-10 secretion overall, whereas the haplotype IL10.R3/IL10.G7 was associated with lowest IL-10 secretion. These data demonstrate that the ability to secrete IL-10 can vary in man according to the genetic composition of the IL-10 locus.

Figure 1

Frequency of IL-10 haplotypes. The number of times each haplotype was observed was expressed as a percentage of the total number of haplotypes (n = 156).

Figure 2

(A) IL-10 secretion in relation to IL-10 locus haplotype. IL-10 secretion was determined following LPS stimulation of whole blood cultures as described in the text. IL-10 haplotypes were also so determined and considered against the levels of secreted IL-10. The medians and semi-interquartile ranges of IL-10 secretion are shown for each haplotype, which was observed four or more times. Levels of IL-10 secretion in these groups were examined simultaneously by the Kruskal-Wallis test of variance analysis; the given P value (P = 0.024) shows that the IL-10 secretion varied significantly between the haplotypes. The indicated haplotypes (∗∗) had the largest positive (R2.G14) or negative (R3.G7) variation from the overall median, as indicated by their z value. (B) Haplotypes associated with high or low IL-10 secretion. The haplotypes indicated from the Kruskal-Wallis analysis were compared with other haplotypes in respect to associated IL-10 secretion. In panel 1, the R2.G14 haplotype is shown to be associated with significantly higher IL-10 secretion than all other haplotypes (P = 0.027) and is strongly suggested to be associated with higher IL-10 secretion than all other IL10.R2-containing haplotypes (P = 0.065). In panel 2, the R3.G7 haplotype is shown to be associated with significantly lower IL-10 secretion than all other haplotypes (P = 0.006) and all other R3-containing haplotypes (P = 0.021). Data are the medians and semi-interquartile ranges. Asterisks indicate statistical significance.

Figure 3

IL10.R3-containing genotypes are associated with lower IL-10 secretion. Genotypes containing various IL10.R alleles were compared in respect of their association with IL-10 secretion, independently of the IL10.G allele present. In panel 1, all available genotypes at IL10.R were compared simultaneously by the Kruskal-Wallis test of variance analysis. This test showed that the IL-10 secretion varied between the groups, with a strong trend to significance (P = 0.04) and that the IL10.R3-homozygous genotypes (∗∗) varied most from the overall median (z = −1.96). In panel 2, IL10.R3-containing genotypes are shown to be associated with significantly lower IL-10 secretion than all other IL10.R-containing genotypes (∗∗; P = 0.011). Data are the medians and semi-interquartile ranges. This analysis included five additional unrelated individuals for whom IL10.R genotypes were known, but unambiguous haplotypes were unavailable.