01 (95% CI 0.70–1.44; P=0.97), respectively, compared with the 1513 A and −762 T alleles. Polymorphisms at the 1513 locus had a statistically significant association with P2X7 variants

and tuberculosis susceptibility, while the −762 locus allele variants were not significantly associated with P2X7 variants and tuberculosis susceptibility. Tuberculosis is a major cause of morbidity and mortality worldwide, especially in Asia and Africa. Genetic variability, combined with environmental factors, are expected to contribute to the risk of developing active tuberculosis (Cooke & Hill, 2001). Human P2X7, which encodes the P2X7 receptor, has been cloned and mapped to human chromosome 12q24 and linked to tuberculosis susceptibility (Buell et al., 1998). The MEK inhibitor P2X7 receptor is a ligand-gated cation channel that is highly expressed on human and murine macrophages (Nicke

et al., 1998; Gu et al., 2001). The activation of P2X7 by adenosine Compound Library chemical structure triphosphate (ATP) causes the immediate opening of a cation-selective channel, allowing the influx of Ca2+ and Na+ and the efflux of K+. This initiates a number of downstream signaling events, including caspase activation, resulting in apoptosis and phospholipase D (PLD) activation, which promotes phagosome–lysosome fusion, resulting in mycobacteria death (Humphreys et al., 2000; Kusner & Barton, 2001; Coutinho-Silva et al., 2003). P2X7 is highly polymorphic and several single nucleotide polymorphisms (SNPs) that

lead to loss of receptor function have been described (Fernando et al., 2005; Shemon et al., 2006). The most common is the 1513AC polymorphism, resulting in a glutamic acid to alanine substitution at position 496. This substitution results in the expression of a nonfunctional P2X7 receptor in macrophages from subjects homozygous for the 1513 C allele and patients heterozygous at this locus have impaired P2X7 receptor function. Additionally, the −762TC SNP Adenosine triphosphate in the P2X7 promoter region has been shown to be protective against tuberculosis in a Gambian population (Li et al., 2002). However, there is no evidence that the −762 C allele has functional consequences for gene expression. Several studies have looked at associations between the P2X7 gene 1513 and −762 loci allele variants and susceptibility to tuberculosis; however, these analyses have yielded mixed results depending on the population studied, in part due to the lack of adequate statistical power, selection bias or population diversity. Because a metaanalysis may overcome some of these methodological difficulties, a systematic review of the literature using metaanalysis was carried out as a means of providing a quantitative estimate on the association between P2X7 polymorphisms and susceptibility tuberculosis. To the best of our knowledge, no metaanalysis of the literature exploring the relationship between P2X7 gene polymorphisms and susceptibility to tuberculosis has been carried out to date.