In this pooled investigation of TLR gene polymorphisms in three case–control studies of NHL, we found consistent evidence that variation in the TLR10–TLR1–TLR6 region is associated with disease risk. Global tests of association across all genotyped variants in this region were statistically significant. In particular, two SNPs within the region, rs10008492 and rs4833103, were significantly associated with NHL; these SNP associations were observed in all the three studies and did not appreciably differ by histologic subtype. We did not observe clear evidence of association with variation in TLR2, although the variant rs3804100 was significantly associated with MZL. No associations with TLR4 variants were observed.
are located in a gene cluster spanning 57 kb on chromosome 4p14. TLR-1 and -6 are important elements of TLR-2 signaling; these polypeptides, which bind tri-acyl and di-acyl lipoproteins, respectively, interact with TLR-2 to create heterodimer receptors capable of recognizing a broad spectrum of pathogen ligands (2
). The ligand and function of TLR-10 are not known, although this receptor has been shown to be expressed in normal and malignant B lymphocytes (8
). There is evidence that genetic variation in the TLR10
region may influence risk of inflammatory diseases; associations with asthma (10
) and aspergillosis following allogeneic stem cell transplantation (28
) have been reported. Associations with TLR10
variants were also observed in a large case–control study of prostate cancer (12
), although a subsequent study of this region reported null findings (29
The functional relevance of the tag SNPs rs10008492, located 8.5 kb telomeric of TLR10
, and rs4833103, located 9.1 kb centromeric of TLR1
and 12.9 kb telomeric of TLR6
, has not been investigated. If our observed associations are real, it is probably that these two variants do not directly influence NHL susceptibility but rather are markers for one or more underlying causal variants. Given the strong LD throughout the TLR10
region (), it is difficult to infer a specific effect of any one of these genes from these SNP findings. It is worth noting though that, within the HapMap CEU sample, both variants exhibit LD with the non-synonymous TLR1
SNP I602S, which has been shown to exhibit reduced activity toward tri-acyl lipoproteins in two studies (30
). It is possible that I602S and/or other functionally relevant TLR1
variants such as P315L (32
) directly influence NHL risk. However, we cannot rule out TLR10
as susceptibility loci; indeed, a rare non-synonymous TLR6
SNP was significantly associated with NHL risk in a recent case–control analysis (9
). Additional investigations involving a fine-mapping approach to TLR10
will be important for identifying the underlying causal variants in this region.
We did not observe clear evidence of association between TLR2
variants and risk of all NHL; the likelihood ratio test was statistically significant, but findings from other analyses were null or equivocal. The TLR2
region tag SNPs rs11935252 and rs7695605 were associated with NHL at a moderate level of statistical significance; however, as both variants actually reside within the neighboring gene RNF175
, involved in metal ion binding, it is unclear what gene effect would be responsible for those associations (if real). We did observe a strong association with MZL risk for the variant rs3804100, both overall and within two of the three studies. No TLR2
variants were associated with other NHL subtypes. Nieters et al.
) reported a statistically significant association with FL for the TLR2
−16933T>A (rs4696480) variant. This SNP was not genotyped in our study, although we note that it resides within a LD block shared by three SNPs included in our study (rs6835636, rs4696187 and rs13150331) in the HapMap CEU sample.
haplotypes including rs3804100 have been previously associated with risk of type 1 diabetes and severity of genital herpes simplex virus type 2 infection (33
). If our observed association with rs3804100 is real, it is most probably that this SNP, which is synonymous (S450S), is a marker for another causal variant. Several non-synonymous SNPs within the TLR2
exon have been identified, including the putatively functional variant Arg753Gln (rs5743708) (35
), although most are rare. An association between TLR2
and MZL is biologically plausible given the strong evidence linking specific infectious organisms to the pathogenesis of MZL, MALT lymphoma in particular (38
), and the importance of TLR-2 in recognizing these organisms. There is convincing evidence that H.pylori
infection is a causal factor for gastric MALT lymphoma, the most common type of extranodal MZL (39
). Other infectious organisms have also been linked to MALT lymphomas at other anatomic sites, including Borrelia burgdorferi
), Chlamydia psittaci
), Campylobacter jejuni
) and the hepatitis C virus (45
). Interestingly, TLR-2 has been shown to play an important role in mediating immune responses to H.pylori
) and hepatitis C virus (50
Genetic variation in TLR4
was not associated with NHL risk in our study. There is conflicting evidence from smaller studies regarding an association of the TLR4
polymorphism Asp299Gly (rs4986790) with NHL; this variant was associated with increased risk of MALT lymphoma in one study (6
) and with decreased risk of MALT lymphoma (7
) and DLBCL (5
) in two others. Our findings for this SNP were consistently null, both overall and for specific subtypes.
Strengths of this pooled analysis include its large size and the population-based design of the three participating case–control studies. It is unlikely that our findings are the result of bias due to population stratification, as race was adjusted for in regression modeling, and analyses restricted to non-Hispanic Caucasians yielded virtually identical findings. Given that we investigated several variants across the three gene regions for both all NHL and different subtypes, we must consider the possibility that our observed associations are false-positive findings. The consistency of our key findings across the three participating studies suggests that they are not due to chance; however, these results require replication in other studies before meaningful inferences regarding causation are drawn.
In conclusion, this pooled investigation of TLR gene variants across the three case–control studies of NHL provides strong evidence that variation in the TLR10
region is associated with risk and suggests that TLR2
variants may influence susceptibility to MZL. Additional studies are needed to replicate these findings and, more generally, to explore further the relevance of TLR pathways to the pathogenesis of NHL. Pooled investigations within the InterLymph Consortium (51
) will be especially informative in this regard.