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| Study | Country | Included study no. | Study search date | Included patients no. | Searched databases | Gene site | Analyzed gene model | Publication bias assessment | Conclusion |
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| Cai et al. [20] | China | 10 Studies from 8 articles for -607 A/C; 9 studies from 6 articles for -137 C/G | January 2013 | 2,662 Cases and 2,168 controls for -607 A/C; 1,331 cases and 1,468 controls for -137 C/G | PubMed, EMBASE, Spring-link, Web of Science, Wanfang (Chinese), and CNKI | -607 A/C, -137 C/G | Allele model, codominant model, dominant model, recessive model | Begg’s funnel plot and Egger’s test, no publication bias | IL-18 (-607 A/C) polymorphism may be associated with RA risk |
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| Chen et al. [21] | China | 7 Studies for -607 A/C; 5 studies for -137 C/G | April 2012 | 1,958 Cases and 1,707 controls for -607 A/C; 333 cases and 541 controls for -137 C/G | PubMed, EMBASE, Web of Science, CNKI, CBMD, and Wanfang (Chinese) | -607 A/C, -137 C/G | Allele model, dominant model, recessive model | Modified Egger’s linear regression test, no publication bias | IL-18 (-607 A/C) polymorphism may confer susceptibility to RA in Chinese population, but not all Asians |
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| Ji and Lee [22] | South Korea | 7 Studies for -607 A/C; 5 studies for -137 C/G; 2 studies for -920 T/C | October 2012 | 2,944 Cases and 2,377 controls for -607 A/C; 1,319 cases and 1,211 controls for -137 C/G; 1,873 cases and 1,092 controls for -920 T/C | MEDLINE, PubMed | -607 A/C, -137 C/G, -920 T/C | Allele model, dominant model, recessive model, homozygote model | Begg’s funnel plots and Egger’s test, with publication bias for -607 A/C in all comparison models, without publication bias for -137 C/G in all comparison models | No significant association was found between two IL-18 (-607 A/C, -137 C/G) polymorphism and RA susceptibility in all subjects; IL-18 (-920 T/C) polymorphism is associated with RA susceptibility |
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| Li et al. [23] | China | 14 Studies from 13 articles for -607 A/C; 11 studies from 10 articles for -137 C/G; 2 studies for -920 T/C; 1 study for -105 C/A | May 1, 2015 | 3,728 Cases and 3,213 controls for -607 A/C; 1,982 cases 1,947 controls for -137 C/G; 1,873 cases 1,091 controls for -920 T/C; 201 cases 218 controls for -105 C/A | PubMed, Ovid, Cochrane Library, EMBASE, and China Knowledge Resource Integrated Database | -607 A/C, -137 C/G, -920 T/C, -105 C/A | Homozygote model, heterozygote model, dominant model, recessive model, additive model | Funnel plots and the Begg test, no publication bias | The -607 A/C, -920 T/C, and -105 A/C polymorphisms in IL-18 were significantly associated with increased RA risk. However, the -137 C/G polymorphism was not associated with RA risk under any genetic model |
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| Pan et al. [24] | China | 4 Studies from 3 articles | May 2010 | 756 Cases and 756 controls | MEDLINE and PubMed | -607 A/C | Recessive model, dominant model, allele model | Begg’s funnel plot and Egger’s test, no publication bias | Not enough evidence to indicate the association of IL-18 gene promoter -607 A/C polymorphism and the development of RA |
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| Song et al. [25] | Korea | 7 Studies for -607 A/C; 7 studies from 6 articles for -137 C/G | January 2013 | 2,894 Cases and 2,361 controls for -607 C/A; 1,596 cases and 1,478 controls for -137 C/G | MEDLINE and EMBASE | -607 A/C, -137 C/G | Allelic model, recessive model, dominant model, homozygote model | Funnel plots, no publication bias | IL-18 (-607 A/C and -137 C/G) polymorphisms are not associated with RA |
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| Wen et al. [26] | China | 5 Studies | Not reported | 1,224 Cases and 1,368 controls | PubMed, EMBASE, and Cochrane library databases | -137 C/G | Dominant model, recessive model, additive model | Funnel plot and Egger’s regression test, no publication bias | IL-18 (-137 C/G) was a risk factor for RA, especially for RA in Europeans |
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