TNF-α production, suggesting a genetic component of approximately 75% and 60%, respectively.18 Interpersonal differences in the regulation of IL-10 and TNF-α production may be critical with respect to the final outcome of an inflammatory response, that is within physiological limits or pathological ones.18 Several polymorphisms located close to or within the IL-10 and TNF-α genes have been shown to be associated with transcription levels. The best-documented of these polymorphisms are the IL-10 gene promoter polymorphisms -1082 G to A, 716,1923 and a G to A transition at position 308 in the promoter region of TNF-α.11, 13, 24, 25 In the presence of allele -1082A, stimulation of lymphocytes with concanavalin A resulted in lower IL-10 production than in allele -1082A negative cells.14, 21 Also, the effects of this allelic promoter region difference (relative to the transcription start site) on IL-10 gene activation have been confirmed in reporter gene assays.20 Concerning TNF-α, there are also data relating the rare -308A allele to a higher transcriptional activity than the common -308G allele,11, 13, 24, 25 although a lack of such an association has also been reported in non-white populations depending on the HLA ancestral haplotype carrying this SNP.12, 24 However, the functional relevance of these SNPs has been shown by their involvement in determining susceptibility to immune-inflammatory diseases (for IL-10 -1082G to A14, 20, 26-35 for TNF-α11,13,24,25,36-42). Genotypic and allelic frequencies were evaluated by gene count. The data were tested for the goodness of fit between the observed and expected genotype values (χ2 test) and their fit to Hardy-Weinberg equilibrium. χ2 tests (3x2 tables or 2x2 tables) were performed to calculate significantly different genotype or allele distributions between centenarians and controls.

RESULTS

Table 1 shows the frequency of homozygous and heterozygous genotypes for 1082 G to A IL-10 SNP and for 308 G to A TNF-α in our sample of Italian centenarian men and sex-matched controls. The number of centenarians homozygous for the 1082G genotype was significantly increased in this cohort of centenarian men in comparison with younger control subjects (p=0.019). Accordingly, the SNP distribution between centenarians and controls was significantly different, with the 1082G allele increased in centenarians (0.69 vs. 0.56, p=0.01 by χ2 test). As already reported,7 no significant differences were observed in women between centenarians and controls (1082G, 0.62 vs. 0.59, p=NS by χ2 test). The genotypic frequencies of the TNF-α promoter SNP of centenarian and control men were not statistically different.

Table 2

Functional IL-10/TNF-α genotypes
TNF-α -308A carrier (A/A, A/G) TNF-α -308G/G IL-10
-1082A carrier (A/A, A/G) Low IL-10, high TNF-α Low IL-10, low TNF-α IL-10
-1082G/G High IL-10, high TNF-α High IL-10, low TNF-α

IL-10 -1082A carriers are classified as low IL-10 producers; IL-10 -1082GG homozygotes are classified as high IL-10 producers; TNF-α -308A carriers are classified as high TNF producers; TNF-α -308GG homozygotes are classified as low TNF producers. For references, see text.

(QLK6-CT-1999-02031). Professor C Franceschi was funded by MIUR, Rome (ex 40%), Ministry of Health projects (1998 and 2001 Chronic diseases prevention in ageing: the model of centenarians and Biological and genetic markers of successful and unsuccessful ageing). LC is a PhD student in Pathobiology.

The isolated assessment of cytokine genotypes may be misleading without considering other interacting cytokines. In vivo control of TNF-α synthesis is complex and downregulated by anti-inflammatory cytokines, including IL-10.12, 13 The potential biological importance of this finding was highlighted by a recent study showing a strong association between the combined low IL-10/high TNF-α genotype and early graft rejection in heart transplant recipients.14 OtherLimitations: Since this study was conducted with Italian centenarians, it is unclear whether the findings can be extended to other ethnic populations. Notably, in a Finnish population, IL-10 and TNF-a promoter allele and haplotype frequencies were not different between nonagenarians and controls.47 Moreover, no significant association between cytokine polymorphisms and longevity has been found in the Sardinian population.48 Overall, these findings suggest that cytokine/longevity associations might have a population-specific component, affected by the population-specific gene pool as well as by gene-environment interaction. Another limitation of the study was the lack of data regarding plasma levels of IL-10 and TNF-a. However, the functional relevance of the studied polymorphisms is well known (see above). Besides, some may argue that a Bonferroni-type adjustment should be performed to correct for testing multiple polymorphisms. If this correction is carried out, none of the polymorphisms would have been significantly associated. However, this correction is too stringent and has the potential to ignore important observations49 and, in any case, for studies on centenarians, increasing the number of cases is very challenging. Nonetheless, inflammatory markers predict disability and mortality in elderly cohorts, and a persistent inflammatory state has been proposed to be involved in the causal pathway of certain age-related chronic conditions.1 3 50 Therefore, it is intriguing that possession of an anti-inflammatory genotype is significantly increased in male centenarians.