The influence of genetic variation on innate immune activation in an environment with high infectious pressure.

Interleukin-10 (IL-10) production is under tight genetic control in populations living in affluent environments. However, little is known about the role of IL10 genetics on cytokine production in populations living in environments with high infectious pressure. We have previously reported that, in a rural Ghanaian population, the most common IL10 haplotype associates with a pro-inflammatory response. Here, we aim to replicate these findings in an independent sample of the same population 2 years later. IL-10 and tumour necrosis factor-α (TNF-α) protein concentrations were determined in whole-blood samples ex vivo stimulated with lipopolysaccharide and zymosan in 2006 (n=615) and 2008 (n=647). The association between IL10 single nucleotide polymorphisms and Z-scores of IL-10 and TNF-α levels was analysed in each population subset. The most common IL10 haplotype was associated with a significantly lower IL-10 production and nonsignificantly increased TNF-α levels. The correlation between repeated cytokine assays, based on 111 individuals with measurements in both 2006 and 2008, was r=0.53 (P<0.001) for IL-10 and r=0.36 (P<0.001) for TNF-α. The replication of our previously found effect of variation in the IL10 gene on IL-10 production and the correlation between repeated cytokine stimulation assays provide evidence that IL10 genetics have an important role in regulating the host response under high infectious pressure.

The effect of common genetic variation in 11ß-hydroxysteroid dehydrogenase type 1 on hypothalamic-pituitary-adrenal axis activity and incident depression.

BACKGROUND: Accumulating evidence suggests that hyperactivity of the hypothalamic-pituitary-adrenal axis (HPA axis) is involved in depression. 11ß-Hydroxysteroid dehydrogenase type 1 (11ß-HSD1) converts inert cortisone to active cortisol and is implicated in HPA axis regulation in animal studies. The aim of our study was to identify polymorphisms in 11ß-HSD1 gene (HSD11B1) with consistent associations with increased HPA axis activity and relate those polymorphisms to depression. METHODS: Twelve single-nucleotide polymorphisms (SNPs), including 11 tagging SNPs, were selected using the HapMap database and genotyped in 4228 participants of the population-based Rotterdam Study. The outcome measures were salivary cortisol levels after awakening, 30 min later, at 1700 h, at bedtime, and plasma levels of androstenedione (in women only). SNPs that were significantly associated with cortisol as well as androstenedione levels were also related to incident depression. RESULTS: rs11119328 was associated with higher cortisol saliva samples collected at bedtime as well as higher androstenedione levels (P value after correction for multiple testing: 0.01 and 0.04, respectively). Carriers of this polymorphism had an increased risk of an incident depression (hazard ratio 1.28, 95% confidence interval 1.03-1.59). Two other SNPs, which were in high linkage disequilibrium with rs11119328, were related to higher cortisol levels but not with androstenedione levels. CONCLUSIONS: We identified one SNP, which was associated with increased salivary cortisol levels at nadir as well as higher androstenedione levels. Moreover, this SNP was also associated with a higher risk of an incident depression. This suggests that 11ß-HSD1 is implicated in human HPA axis regulation and susceptibility to depression.

Performance of the whole-blood stimulation assay for assessing innate immune activation under field conditions.

Innate propensity of immune activation is reflected in production of pro- and anti-inflammatory cytokines upon stimulation of Toll-like receptors (TLR) in whole-blood stimulation assays. The validity of the whole-blood stimulation assay under field conditions has not been evaluated extensively. Here, we have determined correlation of individually repeated whole-blood stimulation assays in a field-study in Ghana and compared it with that of two Dutch populations performed under optimal conditions. We also examined cytokine production to various TLR-agonists in order to create an assay that would mimic general innate immune responses. Under field conditions repeated assessments of lipopolysaccharide-induced Tumor Necrosis Factor-alpha (TNFalpha) production were poorly correlated (r=0.15, p=0.087). Correlation was relatively high for production of Interleukin-10 (IL10) (r=0.48, p<0.001) and comparable to that observed in the Dutch population under optimal conditions. Combined stimulation with lipopolysaccharide and zymosan resulted in cytokine production profiles that were similar to that attained after stimulation with a mixed culture of bacteria. Here, we conclude that variation of a whole-blood assay performed in field setting is large in general but that production of IL10 seems to better reflect an innate pro- or anti-inflammatory tendency whereas production of TNFalpha may predominantly reflect recent immunological challenges. Furthermore, simultaneous stimulation of several Toll-like receptors may mimic general innate immune activation.

C. elegans DAF-12, Nuclear Hormone Receptors and human longevity and disease at old age.

In Caenorhabditis elegans, DAF-12 appears to be a decisive checkpoint for many life history traits including longevity. The daf-12 gene encodes a Nuclear Hormone Receptor (NHR) and is member of a superfamily that is abundantly represented throughout the animal kingdom, including humans. It is, however, unclear which of the human receptor representatives are most similar to DAF-12, and what their role is in determining human longevity and disease at old age. Using a sequence similarity search, we identified human NHRs similar to C. elegans DAF-12 and found that, based on sequence similarity, Liver X Receptor A and B are most similar to C. elegans DAF-12, followed by the Pregnane X Receptor, Vitamin D Receptor, Constitutive Andosteron Receptor and the Farnesoid X Receptor. Their biological functions include, amongst others, detoxification and immunomodulation. Both are processes that are involved in protecting the body from harmful environmental influences. Furthermore, the DAF-12 signalling systems seem to be functionally conserved and all six human NHRs have cholesterol derived compounds as their ligands. We conclude that the DAF-12 signalling system seems to be evolutionary conserved and that NHRs in man are critical for body homeostasis and survival. Genomic variations in these NHRs or their target genes are prime candidates for the regulation of human lifespan and disease at old age.