Stimulation of human blood cultures with bacterial lipopolysaccharide (LPS) shows large interindividual 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.

Interleukin-10 (IL-10) is an important regulatory cytokine whose involvement extends into diverse areas of the human immune system. Recent characterization of the promoter and 5' flanking regions has demonstrated the presence of positive and negative regulatory segments in the promoter. In addition, the characterization of two dinucleotide repeat elements immediately upstream of the gene has shown that there is considerable polymorphism directly associated with the human IL10 gene. In the present report, we describe the mapping of the human IL10 gene to a discrete area of chromosome 1, the definition of a potential cytokine-responsive segment 3 - 4 kilobases upstream of the transcription initiation site, and the identification of two new point mutations in the immediate promoter region with their distribution in a panel of 75 unrelated healthy individuals. These data should further the understanding of how the IL10 gene is controlled in humans and how its function may vary between individuals.

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Interferon lambda-1 (IFN-l1/IL-29) is a member of the Type-III interferon family, which contains three ligands: IFN-l1, 2 and 3. These three ligands use the same unique heterodimeric receptor composed of CRF2-12 (IFN-l-R1/IL-28Ra) and CRF2-4 (IL10-R-b) chains. Like their close relatives, the Type-I interferons, IFN-l1, 2 and 3, promote the phosphorylation of STAT1 and STAT2, induce the ISRE3 complex, elevate OAS and MxA expression and exhibit antiviral activity in vitro. Their use of the IL10-R-b chain and their ability to phosphorylate STAT3, STAT4 and STAT5 suggested that they may also exhibit immunomodulatory activity; their antiviral action led us to hypothesize that this activity might be directed toward the Th1/Th2 system. Here, we have demonstrated that IFN-l1 altered the activity of Th cells in three separate experimental systems: (i) mitogen stimulation, (ii) mixed-lymphocyte reaction (MLR) and (iii) stimulation of naive T cells by monocyte-derived dendritic cells (mDC). In Con-A stimulation assays, the inclusion of IFN-l1 consistently led to markedly diminished levels of secreted interleukin (IL-13) with occasional coincident, modest elevation of secreted IFN-g. IL-13 secretion was 100-fold more sensitive to IFN-l1 than was IFN-g secretion. These observations were also made in the allogeneic two-way MLR. IFN-l1 was able to alter cytokine-mediated Th biasing and when naive T cells were exposed to allogeneic mDC that had been matured in the presence of IFN-l1, secreted IL-13 was again markedly and consistently reduced, whereas secreted IFN-g was largely unaltered. These functions were independent of IL-10. Our data support a hitherto unsuspected role for IFN-l1 in modulating the development of Th1 and Th2 cells, with an apparent emphasis on the diminution of IL-13 secretion.