IL-10 Polymorphisms and Tuberculosis Susceptibility: An Updated Meta-Analysis.

PURPOSE: The association of interleukin-10 (IL-10) polymorphisms (-1082G/A, -819C/T, -592A/C) and interleukin-6 (IL-6) poly-morphisms (-174G/C) with tuberculosis (TB) risk has been widely reported. However, the results are controversial. To clarify the role of these polymorphisms in TB, we performed a meta-analysis of all available and relevant published studies.
MATERIALS AND METHODS: Based on comprehensive searches of the PubMed, Medline, Embase, Web of Science, Elsevier Science Direct and Cochrane Library database, we identified outcome data from all articles estimating the association between IL-10 and IL-6 polymorphisms and TB risk.
RESULTS: The results indicated significant association of the allele model, heterozygous model and dominant model of IL-6 -174G/C polymorphism with decreased risk of TB. In the stratified analysis by ethnicity, significantly increased risk was observed for IL-10 -1082G/A polymorphism in Europeans under recessive model, for IL-10 -819C/T polymorphism in Asians under heterozygous model and dominant model and IL-10 -592A/C polymorphism in Asians under Allele model, homozygous model and recessive model. Moreover, significantly decreased risk of TB was associated with Asians for IL-6 -174C/G polymorphism in allele model, heterozygous model and dominant model. We also performed the analyses by sample types in IL-10 -1082G/A polymorphism, and observed significantly increased TB risk in mixed group under homozygous model.
CONCLUSION: The results suggested that the IL-10 -1082G/A polymorphism is associated with increased TB risk in Europeans, while IL-10 -819C/T and IL-10 -592A/C polymorphisms in Asians. However, IL-6 -174G/C polymorphism might be a genetic risk factor that decreases TB susceptibility in Asians.

INTRODUCTION

Tuberculosis (TB) is one of the important leading causes of death in humans, and it remains a serious public health obstacle in the developing countries. It is estimated that 1.4 million people annually die due to this treatable disease and 9 million incident cases of TB are estimated globally.1 According to the report, Mycobacterium tuberculosis (MTB) infect about one-third of population; however, only approximately one-tenth of those infected will ever develop active TB, which indicate that MTB infection is the result of the interplay between host genetic susceptibility and environmental factors.2

Interleukin-10 (IL-10) is a multifunctional regulatory cytokine of inflammatory responses. Increasing numbers of studies3 have demonstrated that IL-10 acts as a general inhibitor of proliferative and cytokine responses of both T helper (Th) 1 and Th2 cells in vitro and in vivo. IL-10 plays an anti-inflammatory action by suppressing the production of cytokines such as IL-1α, IL-1β, IL-6, IL-8, IL-12, and tumor necrosis factor-alpha in activated macrophage and interferon gamma in T cells. The IL-10 gene is located on chromosome 1 (1q31-1q32) with five exons. The promoter region of IL-10 gene has been found to be highly polymorphic and its many polymorphisms have been identified.4 In the past few years, the impact of three common polymorphisms in the promoter of IL-10 gene -592A/C, -1082 G/A, and -819C/T on susceptibility to TB have been reported, and results suggested that these polymorphisms contribute to the risk of TB by affecting IL-10 transcription level, but the findings are controversial.

The human interleukin-6 (IL-6) gene is located at 7p21-24 locus with an upstream promoter containing 303 bp. IL-6 is a pleiotropic cytokine, secreted as a T-cell derived factor by a variety of cell types including lymphocytes, monocytes, and endothelial cells. It has endocrine as well as paracrine and autocrine actions implicated in several physiologic and pathologic processes including immunity and inflammation, activation of fibroblasts, mast cells, endothelial cells, monocytes, and keratinocytes.5 Furthermore, the genetic polymorphism in the IL-6 promoter (-174G/C) that influences its transcription rate might play a crucial role in host immunity and susceptibility to TB.6

A relatively large number of studies found the association between IL-10 and IL-6 polymorphisms and TB risk, however, the results have been inconsistent and inconclusive due to limited sample sizes and different study populations. Therefore, we performed this meta-analysis on all eligible case-control studies to estimate the effect of polymorphisms in the IL-10 and IL-6 genes on the risk of TB.

MATERIALS AND METHODS

Identification of relevant studies

Relevant publications were identified with a literature search using terms "IL-10" or "Interleukin-10" or "IL-6" or "Interleukin-6" and "tuberculosis" or "TB" or "TB infection" or "TB disease" and "polymorphism" or "genotype" or "variant" in the PubMed, Medline, Embase, Web of Science, Elsevier Science Direct and Cochrane Library database (the last search update was 1 February 2014), and the search was limited to English-language journals. Additional studies were identified by a manual search of the references of original studies. The following criteria were used for inclusion in the analysis: 1) a case-control or cohort design was used and 2) studies contained available genotype frequencies. The major reasons for exclusion of studies were: no usable data were reported.

Data extraction and quality assessment

Two investigators independently extracted data and jointly reached a consensus on all of the studies researched. The following data were collected from each study: first author's name, publication year, original country, ethnicity, number of cases and controls, genotype frequencies for cases and controls, Hardy-Weinberg equilibrium (HWE) of controls and Newcastle-Ottawa Scale (NOS).7 Star symbol was used to denote the quality, based on 3 aspects of the study: selection, comparability, and exposure. Studies with a score of 7 stars or greater were considered to be of high quality.

Statistical analysis

The risks [odds ratios (ORs), and 95% confidence intervals (95% CIs)] of TB associated with IL-10 and IL-6 polymorphisms were estimated for each study based on extracted genotype data. The statistical significance of the pooled OR was determined using the Z-test. Heterogeneity assumption was examined by the Cochran's Q-test. If Q-test indicated p<0.10, thus indicating a lack of heterogeneity among studies, then the fixed effect model was used (the Mantel-Haenszel method).8 Otherwise, the random-effects model (the DerSimonian and Laird method)9 was performed. Sensitivity analysis was mainly performed to assess the stability of the results, namely, a single study in the meta-analysis was deleted to reflect the influence of the individual data set on the pooled OR. Asymmetry funnel plots were inspected to assess potential publication bias. The Egger's linear regression test was also used to assess publication bias statistically. All the above statistical analyses were performed by using the software Stata Version 12.0 (Stata Corporation, College Station, TX, USA) and p values were two-tailed.

RESULTS

Literature search and characteristics of eligible studies

The flow chart that displays the study selection process is shown in Fig. 1. The search of the selected databases retrieved 30 potentially relevant articles, including 7800 cases and 8793 controls, according to inclusion and exclusion criteria. There are 26 case-control studies concerning IL-10 -1082G/A polymorphism,610111213141516171819202122232425262729303132333435 15 case-control studies for IL-10 -819C/T polymorphism,61014161720212224252829303236 16 case-control studies for IL-10 -592A/C polymorphism,6101415161720212425262930323336 and 7 case-control studies about IL-6 -174G/C polymorphism. 6161721253738 Among the 30 eligible studies, 14 of them were of Asians,611151819212223283031353738 6 studies were of Europeans,121316202534 6 studies were of Africans,101424272936 and 4 studies were of Americans.17263233 The NOS scores ranged from 7 to 9, indicating that the methodological quality was generally good. The detailed characteristics of the eligible studies included in this meta-analysis are shown in Table 1, and the genotype and allele distributions of all four polymorphisms are shown in Table 2. The genotype distributions among the controls of all studies were consistent with the HWE except for eight studies for the IL-10 -1082G/A,611132325272934 one study for the IL-10 -819C/T,36 three studies for the IL-10 -592A/C,143336 and two studies for the IL-6 -174G/C (Table 1).616

Fig. 1

Flow diagram for study selection.

Table 1

Baseline Characteristics of the 30 Eligible Studies Included in This Meta-Analysis

Study	Yr	Male patients (%)	Mean age (yrs)		Sample types	Sample size		SNP studied	Clinical diagnoses performed	Control source	Sample tested	Genotyping method	NOS score	P-HWE for controls
			Cases	Controls		Cases	Control
IL-10
Bellamy, et al.10	1998	67.4	34.7±13.2	30.3±7.5	PTB	401	408	-1082G/A, -819C/T, -592A/C	Acidfast, bacilli (AFB)	HB	Blood	PCR-slot-blotting	7	0.824
Delgado, et al.11	2002	37.3	42.2±14.1	37.5±12.9	PTB	356	106	-1082G/A	Sputum smear, medical history, physical examination	HB	Blood	RFLP-PCR	9	<0.001
López-Maderuelo, et al.12	2003	NR	NR	NR	PTB	113	100	-1082G/A	Culture, radiologic diagnosed	HB	Blood	ARMS-PCR	8	0.949
Scola, et al.13	2003	NR	35-60	NR	PTB	45	114	-1082G/A	Clinical history, radiologic diagnosed	PB	Blood	ARMS-PCR	7	<0.001
Fitness, et al.14	2004	NR	NR	NR	PTB	210	705	-1082G/A, -819C/T, -592A/C	Culture, smear, history	HB	Blood	ARMS-PCR	7	0.524
Shin, et al.15	2005	NR	46.9 (18-86)	56.1 (50-81)	PTB	450	851	-1082G/A, -592A/C	AFB	HB	Blood	Single-base extension methods	8	0.168
Amirzargar, et al.6	2006	NR	NR	NR	PTB	41	123	-1082G/A, -819C/T, -592A/C	AFB, chest X-ray (CXR)	HB	Blood	PCR-SSP	8	<0.001
Oral, et al.16	2006	NR	NR	NR	PTB, EPTB	81	50	-1082G/A, -819C/T, -592A/C	Staining of sputum smears, culture, biopsy, radiography	HB	Blood	PCR-SSP	9	0.06
Henao, et al.17	2006	57.9	15-70	17-55	PTB, EPTB	190	135	-1082G/A, -819C/T, -592A/C	Ziehl-Nielssen staining of sputum smears, culture, biopsy, CXR, clinical history	HB	Blood	PCR-SSP	9	0.94
Oh, et al.18	2007	68.9	17-88	45.8 (18-81)	PTB	145	117	-1082G/A	Staining of sputum smears, culture, radiography	HB	Blood	ARMS-PCR	8	0.612
Prabhu Anand, et al.19	2007	56.8	35.5±12.3	29.7±9.5	PTB	132	143	-1082G/A	Staining of sputum smears, culture, radiography	HB	Blood	PCR-RFLP	8	0.123
Ates, et al.20	2008	62	47.84±12.6	54.1±7.2	PTB, EPTB	128	80	-1082G/A, -819C/T, -592A/C	Radiographic, clinical presentation, smears, culture	HB	Blood	ARMS-PCR	9	0.978
Selvaraj, et al.21	2008	71.7	Male: 35.3±10.5, female: 29.2±10.3	Male: 32±8.1, female: 27.1±8.6	PTB	155	183	-1082G/A, -819C/T,	Radiographic, clinical presentation, smears, culture	PB	Blood	PCR-RFLP	7	0.204
Wu, et al.22	2008	NR	NR	NR	PTB	61	122	-1082G/A, -819C/T, -592A/C	Radiographic, clinical presentation, smears, culture	HB	Blood	PCR-RFLP	7	0.379
Ansari, et al.23	2009	NR	NR	NR	PTB	188	188	-1082G/A	Microscopy, culture, histology, imaging	PB	Blood	ARMS-PCR	8	<0.001
Thye, et al.24	2009	NR	NR	NR	PTB	2010	2346	-1082G/A, -819C/T, -592A/C	Smears, culture	PB	Blood	FRET	8	0.542
Trajkov, et al.25	2009	NR	20-59	NR	PTB	75	299	-1082G/A, -819C/T, -592A/C	WHO based	PB	Blood	PCR-SSP	7	<0.001
Taype, et al.26	2010	97.6	29.01±11.42	32.56±9.39	PTB, EPTB	626	513	-1082G/A, -592A/C	Smears, culture, biopsy, clinical	HB	Blood	Taqman PCR	9	0.142
IL-10
Mosaad, et al.27	2010	67.3	0.5 (0.025-1.5)	NR (0.047-1.5)	PTB, EPTB	110	118	-1082G/A	Smear, culture	HB	Blood	ARMS-PCR	9	<0.001
Ma, et al.28	2010	27.8	34.75±16.67	38.17±17.39	PTB	543	544	-819C/T	Radiographic, smears, culture	HB	Blood	ARMS-PCR	9	0.491
Ben-Selma, et al.29	2011	51.9	PTB: 44, EPTB: 39	35	PTB, EPTB	131	95	-1082G/A, -819C/T, -592A/C	Sputum smear, CXR, radiologic, histologic grounds	HB	Blood	PCR-RFLP	9	<0.05
Liang, et al.30	2011	NR	NR	NR	PTB, EPTB	235	78	-1082G/A, -819C/T, -592A/C	Radiographic, biopsy, clinical presentation, smears, culture	HB	Blood	SNaPshot assay	9	0.589
Ramaseri Sunder, et al.31	2012	NR	NR	NR	PTB, EPTB	104	102	-1082G/A	Sputum smear, CXR, biopsy, Fine Needle Aspiration Cytology (FNAC)	HB	Blood	ARMS-PCR	8	0.057
Spinassé, et al.32	2012	NR	NR	NR	PTB	221	271	-1082G/A, -819C/T, -592A/C	Culture	HB	Blood	Sequencing	7	0.189
García-Elorriaga, et al.33	2013	38.9	38-65	26-41	PTB	77	60	-1082G/A, -592A/C	WHO based	HB	Blood	Taqman PCR	7	0.728
Ulger, et al.34	2013	84.5	32.57±15.94	29.40±11.56	PTB, EPTB	84	110	-1082G/A	Smear, culture	HB	Blood	PCR-RFLP	8	<0.001
Meenakshi, et al.35	2013	50	27.4±13.9	30±10.7	PTB	100	100	-1082G/A	Radiographic, sputum culture, AFB, histocytological examination	HB	Blood	ARMS-PCR	8	0.058
Mhmoud, et al.36	2013	69.6	36.9 (15-89)	31.2 (17-85)	PTB	191	206	-819C/T, -592A/C	Culture, smear	HB	Blood	PCR-RFLP	8	<0.001
IL-6
Oral, et al.16	2006	NR	NR	NR	PTB, EPTB	81	49	-174G/C	Staining of sputum smears, culture, biopsy, radiography	HB	Blood	PCR-SSP	9	<0.05
Henao, et al.17	2006	57.9	15-70	17-55	PTB, EPTB	190	135	-174G/C	Ziehl-Nielssen staining of sputum smears, culture, biopsy, CXR, clinical history	HB	Blood	PCR-SSP	9	0.689
Amirzargar, et al.6	2006	NR	NR	NR	PTB	40	119	-174G/C	AFB, CXR	HB	Blood	PCR-SSP	8	<0.05
Selvaraj, et al.21	2008	71.7	Male: 35.3±10.5, female: 29.2±10.3	Male: 32±8.1, female: 27.1±8.6	PTB	160	183	-174G/C	Radiographic, clinical presentation, smears, culture	PB	Blood	PCR-RFLP	7	0.419
Trajkov, et al.25	2009	NR	20-59	NR	PTB	75	301	-174G/C	WHO based	PB	Blood	PCR-SSP	7	0.492
Ansari, et al.37	2011	NR	Minimal/moderate disease: 32.4±15.9; advanced disease: 27±17.0	28.3±12.1	PTB	97	166	-174G/C	Radiographic, smears, culture	PB	Blood	ARMS-PCR	8	0.567
Zhang, et al.38	2012	62	38.64±18.44	36.92±16.52	PTB	495	358	-174G/C	Radiographic, smears, culture	HB	Blood	Mass spectrometry	8	0.979

NR, not report; PTB, pulmonary tuberculosis; EPTB, extra-pulmonary tuberculosis; SNP, single nucleotide polymorphism; PB, population-based controls; HB, hospital-based controls; PCR, polymerase chain reaction; SSP, sequence-specific primers; ARMS, amplification refractory mutation system; RFLP, restriction fragment length polymorphism; NOS, newcastle-ottawa scale; C, confirmed to HWE; HWE, Hardy-Weinberg equilibrium.

Table 2

Genotype and Allele Distributions of IL-10 and IL-6 Polymorphisms in Cases and Controls

Polymorphisms	Study	Country	Ethnicity	Case			Control			Case		Control
				GG	AG	AA	GG	AG	AA	G	A	G	A
IL-10-1082G/A	Bellamy, et al.10	Gambia	African	51	185	165	45	184	179	287	515	274	542
	Delgado, et al.11	Cambodia	Asian	11	259	86	3	64	39	281	431	70	142
	López-Maderuelo, et al.12	Spain	European	33	47	33	29	50	21	113	113	108	92
	Scola, et al.13	Italy	European	17	22	6	24	77	13	56	34	125	103
	Fitness, et al.14	Malawi	African	23	78	69	87	251	203	124	216	425	657
	Shin, et al.15	Korea	Asian	2	53	394	9	124	718	57	841	142	1560
	Amirzargar, et al.6	Iran	Asian	2	31	7	5	79	18	35	45	89	115
	Oral, et al.16	Turkey	European	10	41	30	5	13	32	61	101	23	77
	Henao, et al.17	Colombia	American	32	92	66	26	66	43	156	224	118	152
	Oh, et al.18	Korea	Asian	4	43	98	19	53	45	51	239	91	143
	Prabhu, et al.19	India	Asian	3	55	74	6	61	73	61	203	73	207
	Ates, et al.20	Turkey	European	26	65	37	6	32	42	117	139	44	116
	Selvaraj, et al.21	India	Asian	5	42	102	6	69	108	52	246	81	285
	Wu, et al.22	China	Asian	1	12	48	0	18	104	14	108	18	226
	Ansari, et al.23	Pakistan	Asian	27	132	29	20	136	32	186	190	176	200
	Thye, et al.24	Ghana	African	117	631	793	160	783	1025	865	2217	1103	2833
	Trajkov, et al.25	Macedonia	European	10	48	17	17	212	70	68	82	246	352
	Taype, et al.26	Peru	American	22	187	414	10	153	347	231	1015	173	847
	Mosaad, et al.27	Egypt	African	16	92	2	22	88	8	124	96	132	104
	Ben-Selma, et al.29	Tunisian	African	21	65	45	9	26	60	168.8	155	44	146
	Liang, et al.30	China	Asian	0	28	207	0	9	69	28	442	9	147
	Ramaseri Sunder, et al.31	India	Asian	3	25	76	2	43	57	31	177	47	157
	Spinassé, et al.32	Brazil	American	24	100	97	31	107	133	148	294	169	373
	García-Elorriaga, et al.33	Mexico	American	54	20	3	31	25	4	128	26	87	33
	Ulger, et al.34	Turkey	European	0	84	0	1	104	5	84	84	106	114
	Meenakshi, et al.35	India	Asian	4	81	15	16	59	25	89	111	91	109

IL-10, interleukin 10; IL-6, interleukin 6.

Quantitative synthesis

The summary of the meta-analysis for IL-10 -1082G/A, -819C/T, -592A/C, and IL-6 -174G/C polymorphisms and tuberculosis susceptibility is shown in Table 3.

Table 3

Determination of the Genetic Effects of IL-10 and IL-6 Polymorphisms on TB and Subgroup Analysis

	Allele model		Homozygous model		Heterozygous model		Dominant model		Recessive model
	Effect model OR (95% Cl)	p value	Effect model OR (95% Cl)	p value	Effect model OR (95% Cl)	p value	Effect model OR (95% Cl)	p value	Effect model OR (95% Cl)	p value
IL-10-1082G/A	G allele vs. A allele		GG vs. AA		AG vs. AA		GG+AG vs. AA		GG vs. AG+AA
Ethnicity
Overall	1.05(0.93,1.19)	0.423	1.15(0.87,1.51)	0.320	1.08(0.90,1.29)	0.393	1.09(0.91,1.31)	0.335	1.09(0.87,1.38)	0.448
European	1.34(1.00,1.80)	0.054	1.88(0.93,3.80)	0.079	1.35(0.70,2.63)	0.369	1.49(0.79,2.79)	0.215	F1.69(1.19, 2.39)	0.003
American	F1.10(0.95,1.27)	0.201	F1.16(0.81,1.67)	0.421	F1.07 (0.88,1.30)	0.509	F1.09 (0.90,1,31)	0.372	F1.23 (0.90,1.68)	0.203
Asian	0.85(0.67,1.09)	0.209	0.69(0.36,1.36)	0.285	0.91(0.66,1.26)	0.940	0.89(0.63,1.25)	0.494	0.67(0.36,1.26)	0.212
African	1.12(0.91,1.38)	0.289	1.20(0.81,1.77)	0.369	1.32(0.93,1.87)	0.126	1.31 (0.92,1.88)	0.131	F0.97 (0.81,1.17)	0.761
Sample types
PTB	0.98(0.85,1.12)	0.726	0.93(0.70,1.25)	0.646	0.97(0.81,1.15)	0.691	0.96(0.80,1.15)	0.651	1.01 (0.76,1.34)	0.958
PTB+EPTB	1.23(0.94,1.62)	0.130	2.00(1.16,3.45)	0.013	1.53(0.95,2.49)	0.084	1.56(0.97,2.52)	0.067	1.31 (0.89,1.93)	0.176
IL-10-819C/T	T allele vs. C allele		TT vs. CC		TC vs. CC		TT+TC vs. CC		TT vs. TC+CC
Ethnicity
Overall	F1.01 (0.95,1.07)	0.788	F1.01 (0.89,1.15)	0.834	1.21(1.00,1.46)	0.056	1.14(0.98,1.34)	0.099	F0.93 (0.84,1.03)	0.164
European	F0.92(0.71,1.19)	0.512	F0.75 (0.40,1.42)	0.380	F0.97 (0.68,1.37)	0.846	0.93(0.67,1.30)	0.678	F0.79 (0.43,1.44)	0.438
American	F1.04 (0.85,1.27)	0.732	F1.08(0.71,1.65)	0.721	F1.03 (0.76,1.39)	0.870	F1.04 (0.78,1.38)	0.799	F1.06 (0.72,1.57)	0.756
Asian	F1.08 (0.95,1.23)	0.265	F1.24 (0.92,1.67)	0.157	F1.34 (1.02,1.77)	0.035	F1.31 (1.01,1.70)	0.043	F1.01 (0.84,1.22)	0.897
African	F0.99 (0.92,1.07)	0.812	F0.97 (0.83, 1.13)	0.691	1.34(0.90,2.00)	0.148	1.21 (0.89,1.64)	0.231	F0.88 (0.77,1.01)	0.065
Control source
HB	F1.01 (0.93,1.10)	0.785	F1.04 (0.87,1.24)	0.685	1.20(0.92,1.55)	0.175	1.13(0.92,1.39)	0.237	F0.93 (0.81,1.07)	0.310
PB	F1.01(0.92,1.09)	0.919	F0.99 (0.82,1.19)	0.908	1.26(0.89,1.78)	0.201	1.20(0.88,1.64)	0.258	F0.92 (0.79, 0.84)	0.339
IL-10-592A/C	A allele vs. C allele		AA vs. CC		AC vs. CC		AA+AC vs. CC		AA vs. AC+CC
Ethnicity
Overall	1.07(0.95,1.19)	0.270	1.09(0.89,1.33)	0.401	F1.01 (0.91, 1.12)	0.839	1.06(0.91,1.22)	0.474	1.09(0.93,1.29)	0.291
European	F0.84 (0.65,1.09)	0.181	F0.64 (0.35,1.18)	0.153	F0.90(0.63,1.27)	0.536	F0.85 (0.61,1.18)	0.323	F0.68 (0.38,1.23)	0.204
American	1.01(0.80,1.28)	0.918	F0.93 (0.72,1.20)	0.595	0.91(0.64,1.31)	0.623	0.97(0.67,1.39)	0.859	F1.07 (0.86,1.34)	0.545
Asian	F1.26 (1.08,1.45)	0.002	F1.50 (1.07, 2.12)	0.020	F1.21 (0.88,1.67)	0.250	F1.35 (0.99,1.83)	0.058	F1.33 (1.10,1.62)	0.004
African	1.12(0.91,1.37)	0.290	1.12(0.79,1.58)	0.528	F1.11(0.97,1.27)	0.144	F1.09 (0.96,1.24)	0.175	1.08(0.77,1.52)	0.654
Control source
HB	1.08(0.94,1.24)	0.254	1.14(0.90,1.45)	0.289	F0.95(0.84,1.08)	0.429	1.07(0.89,1.29)	0.464	1.15(0.97,1.37)	0.111
PB	1.00(0.89,1.1 1)	0.933	0.94(0.75,1.19)	0.607	F1.13(0.95,1.34)	0.154	1.08(0.91,1.22)	0.359	0.87(0.71,1.07)	0.194
IL-6-174G/C	C allele vs. G allele		CC vs. GG		CG vs. GG		CC+CG vs. GG		CC vs. CG+GG
Overall	F0.77 (0.64, 0.91)	0.003	F0.67 (0.43,1.05)	0.078	F0.72(0.57, 0.90)	0.005	F0.71 (0.57, 0.88)	0.002	F0.77 (0.50,1.19)	0.243
European	F0.92 (0.67,1.26)	0.594	0.73(0.22,2.43)	0.610	F1.00(0.64,1.57)	0.987	F0.94 (0.62,1.42)	0.773	0.72(0.20,2.59)	0.615
Asian	F0.71 (0.54,0.93)	0.013	F0.69 (0.32,1.48)	0.343	F0.61 (0.44,0.85)	0.004	F0.63 (0.46, 0.86)	0.004	F0.93 (0.44,1.97)	0.855

TB, tuberculosis; PTB, pulmonary tuberculosis; EPTB, extra-pulmonary tuberculosis; PB, population-based controls; HB, hospital-based controls; R, random effect model; F, fixed effect model; IL-10, interleukin 10; IL-6, interleukin 6; CI, confidence interval; OR, odds ratio.

Analysis of IL-10 -1082G/A and TB susceptibility

In all, twenty-six studies consisted of 5949 cases and 6948 controls, and assessed the potential influence of the IL-10 -1082G/A polymorphism with TB susceptibility. Random effects models were used to calculate the pooled OR in all genetic models. Overall, the combined results showed no significant association in all genetic models (Fig. 2A-E). In the stratified analysis by ethnicity, IL-10 -1082G/A polymorphism was associated with a significantly increased risk of TB in European group under recessive model (GG vs. AG+AA: OR=1.69, 95% CI=1.19-2.39). However, no significant association was found in American, Asian and African populations in all tested models. On subgroup analysis by sample types, significantly increased TB risk was observed under homozygous model (GG vs. AA: OR= 2.00, 95% CI=1.16-3.45) in PTB and extra-pulmonary tuberculosis (EPTB) mixed group. The results are shown in Table 3.

Fig. 2

Forest plot of the overall risk of TB associated with the IL-10 -1082G/A and -819C/T polymorphism in all genetic models. Bars represent 95% CI and boxes represent OR values. The size of each box indicates the weight of the study in the pooled results. (F-J) T allele vs. C allele, TT vs. CC, TC vs. CC, TT+TC vs. CC, TT vs. TC+CC for -819C/T. TB, tuberculosis; IL-10, interleukin 10; CI, confidence interval; OR, odds ratio.

Analysis of IL-10 -819C/T and TB susceptibility

As for IL-10 -819C/T, there were fifteen studies involving 4207 cases and 5264 controls for data synthesis in our meta-analysis. The results showed that IL-10 -819C/T polymorphism was not significantly associated with the risk of TB in all genetic models (Fig. 2 F-J ). In the stratified analyses by ethnicity and control source for the -819C/T polymorphism, a significantly increased risk was observed among Asians in heterozygous model and dominant model (TC vs. CC: OR=1.34, 95% CI=1.02-1.77; TT+TC vs. CC: OR=1.31, 95% CI=1.01-1.70). The results are shown in Table 3.

Analysis of IL-10 -592A/C and TB susceptibility

In total, sixteen studies including 4115 cases and 5441 controls examined the relationship between the IL-10 -592A/C polymorphism and TB susceptibility. As shown in Table 3, we failed to find the association between the IL-10 -592A/C polymorphism and TB risk in all genetic models. In the stratified analyses for the IL-10 -592A/C polymorphism, a significantly increased risk was observed among Asians in allele model (A allele vs. C allele: OR=1.26, 95% CI=1.08-1.28), homozygous model (AA vs. CC: OR=1.50, 95% CI=1.07-2.12), and recessive model (AA vs. AC+CC: OR=1.33, 95% CI=1.10-1.62) (Table 3).

Analysis of IL-6 -174G/C and TB susceptibility

A total of 1138 cases and 1311 controls from seven case-control studies were included for data synthesis. A decreased risk between IL-6 -174G/C polymorphism and the risk of TB was observed in Allele model (C allele vs. G allele: OR=0.77, 95% CI=0.64-0.91), heterozygous model (CC vs. GG: OR=0.72, 95% CI=0.57-0.90), and dominant genetic model (CC+CG vs. GG: OR=0.71, 95% CI=0.57-0.88). In the stratified analysis by ethnicity, IL-6 -174G/C polymorphism was associated with a significantly decreased risk of TB in Asian populations in Allele model (C allele vs. G allele: OR=0.71, 95% CI=0.54-0.93), heterozygous model (CC vs. GG: OR=0.61, 95% CI=0.44-0.85), and dominant genetic model (CC+CG vs. GG: OR=0.63, 95% CI=0.46-0.86). The results are shown in Table 3.

Heterogeneity analysis

There were statistically significant heterogeneity in all genetic models for IL-10 -1082G/A polymorphism, heterozygous model and dominant model for IL-10 -819C/T polymorphism, and all genetic models except for heterozygous model for IL-10 -592A/C (Table 3). To elucidate the heterogeneity, Galbraith plots were performed in these genetic models. When the studies which were outliers in some genetic models were excluded respectively, all I2 values were less than 50%, and Pheterogeneity were greater than 0.1 (Fig. 3, Table 4). The significance of pooled OR in all genetic models was not influenced after excluding the studies. By meta-regression analysis, the heterogeneity sources were attributable to the sample types, ethnicity, control source, and the genotyping method. Ethnicity and sample types might be predominant sources of heterogeneity in IL-10 -1082G/A polymorphism, and ethnicity and control source in both IL-10 -819C/T and IL-10 -592A/C polymorphisms (Table 5).

Fig. 3

Galbraith plot of IL-10 promoter polymorphism and TB risk. (A-E) The five studies1820223133 in G vs. A, three studies202231 in GG vs. AA, seven studies13182022313337 in AG vs. AA, six studies131820223133 in GG+AG vs. AA, and five studies2022273537 in GG vs. AG+AA were outliers for -1082G/A. (F and G) The one study38 in TC vs. CC and one study38 in TT+TC vs. CC for -819C/T. (H-K) The three studies262838 in A vs. C, one study38 in AA vs. CC, one study38 in AA+AC vs. CC, and two studies1738 in AA vs. AC+CC for -592A/C. TB, tuberculosis; IL-10, interleukin 10.

Table 4

Meta-Analyses of IL-10 Polymorphisms and Risk of TB after Omitting the Studies

Polymorphisms	Omitted studies	OR (95% CI)	Z	POR	I2 (%)	Pheterogeneity	Effect model
IL-10-1082G/A
G vs. A	Ates, et al.;20 García-Elorriaga, et al.;33 Oh, et al.;18 Ramaseri Sunder, et al.;31 Wu, et al.22	1.02 (0.96, 1.09)	0.69	0.488	9.4	0.336	F
GG vs. AA	Ates, et al.;20 Ramaseri Sunder, et al.;31 Wu, et al.22	1.04 (0.90, 1.21)	0.54	0.588	2.2	0.430	F
AG vs. AA	Ansari, et al.;37 Ates, et al.;20 García-Elorriaga, et al.;33 Oh, et al.;18 Ramaseri Sunder, et al.;31 Scola, et al.;13 Wu, et al.22	1.00 (0.92, 1.09)	0.01	0.989	0.0	0.486	F
GG+AG vs. AA	Ates, et al.;20 García-Elorriaga, et al.;33 Oh, et al.;18 Ramaseri Sunder, et al.;31 Scola, et al.;13 Wu, et al.22	1.01 (0.93, 1.10)	0.25	0.802	11.6	0.311	F
GG vs. AG+AA	Ansari, et al.;37 Ates, et al.;20 Meenakshi, et al.;35 Mosaad, et al.;27 Wu, et al.22	1.03 (0.90, 1.19)	0.46	0.645	0.0	0.623	F
IL-10-819C/T
TC vs. CC	Zhang, et al.38	1.06 (0.96, 1.17)	1.19	0.234	0.0	0.671	F
TT+TC vs. CC	Zhang, et al.38	1.04 (0.95, 1.14)	0.80	0.424	0.0	0.683	F
IL-10-592A/C
A vs. C	Ma, et al.;28 Taype, et al.;26 Zhang, et al.38	1.08 (0.99, 1.17)	1.78	0.075	3.7	0.409	F
AA vs. CC	Zhang, et al.38	0.99 (0.87, 1.13)	0.11	0.913	5.9	0.386	F
AA+AC vs. CC	Zhang, et al.38	1.00 (0.91, 1.10)	0.08	0.936	29.1	0.138	F
AA vs. AC+CC	Henao, et al.;17 Zhang, et al.38	0.96 (0.85, 1.09)	0.63	0.526	0.0	0.845	F

TB, tuberculosis; CI, confidence interval; OR, odds ratio; Pheterogeneity, p value of Q test for heterogeneity; F, fixed-effect models; IL-10, interleukin 10.

Table 5

Multivariate Meta-Regression Analyses of Potential Source of Heterogeneity

Heterogeneity factors	Coefficient	SE	t	p value	95% CI
					LL	UL
Sample types
IL-10-1082G/A (AM, HoM, HeM, DM, RM)	0.234, 0.924, 0.407, 0.433, 0.457	0.183, 0.361, 0.278, 0.279, 0.289	1.28, 2.56, 1.46, 1.55, 1.58	0.215, 0.019, 0.158, 0.136, 0.130	-0.146, 0.170, -0.171, -0.148, -0.146	0.614, 1.679, 0.985, 1.014, 1.061
IL-10-819C/T (HeM, DM)	-0.119, -0.071	0.345, 0.285	-0.35, -0.25	0.737, 0.808	-0.887, -0.706	0.649, 0.564
IL-10-592A/C (AM, HoM, DM, RM)	-0.091, -0.104, -0.162, -0.055	0.158, 0.316, 0.203, 0.235	-0.57, -0.33, -0.80, -0.23	0.577, 0.748, 0.440, 0.819	-0.438, -0.800, -0.609, -0.572	0.256, 0.592, 0.284, 0.462
Ethnicity
IL-10-1082G/A (AM, HoM, HeM, DM, RM)	-0.082, -0.118, 0.014, -0.031, -0.223	0.077, 0.141, 0.124, 0.124, 0.108	-1.07, -0.83, 0.11, -0.25, -2.06	0.298, 0.415, 0.910, 0.804, 0.052	-0.241, -0.413, -0.244, -0.290, -0.448	0.077, 0.177, 0.272, 0.227, 0.002
IL-10-819C/T (HeM, DM)	0.116, 0.082	0.141, 0.115	0.82, 0.71	0.433, 0.493	-0.120, -0.175	0.431, 0.339
IL-10-592A/C (AM, HoM, DM, RM)	0.067, 0.106, 0.084, 0.062	0.067, 0.137, 0.082, 0.110	1.00, 0.78, 1.02, 0.57	0.339, 0.453, 0.329, 0.583	-0.081, -0.195, -0.097, -0.179	0.215, 0,407, 0.264, 0.304
Control source
IL-10-1082G/A (AM, HoM, HeM, DM, RM)	0.093, 0.528, -0.137, -0.057, 0.545	0.207, 0.366, 0.308, 0.311, 0.295	0.45, 1.44, -0.44, -0.18, 1.85	0.659, 0.166, 0.661, 0.855, 0.080	-0.338, -0.239, -0.776, -0.705, -0.070	0.524, 1.295, 0.503, 0.590, 1.161
IL-10-819C/T (HeM, DM)	0.053, 0.051	0.363, 0.294	0.14, 0.17	0.888, 0.867	-0.757, -0.605	0.862, 0.707
IL-10-592A/C (AM, HoM, DM, RM)	-0.157, -0.368, -0.090, -0.395	0.191, 0.362, 0.225, 0.265	-0.82, -1.02, -0.40, -1.49	0.429, 0.331, 0.697, 0.165	-0.577, -1.165, -0.585, -0.978	0.263, 0.429, 0.405, 0.189
Genotyping method
IL-10-1082G/A (AM, HoM, HeM, DM, RM)	0.075, 0.124, 0.051, 0.068, 0.137	0.064, 0.121, 0.098, 0.099, 0.095	1.17, 1.02, 0.52, 0.69, 1.44	0.254, 0.319, 0.606, 0.499, 0.164	-0.058, -0.129, -0.152, -0.137, -0.061	0.209, 0.376, 0.254, 0.273, 0.335
IL-10-819C/T (HeM, DM)	0.006, 0.022	0.131, 0.106	0.05, 0.21	0.965, 0.840	-0.285, -0.214	0.297, 0.257
IL-10-592A/C (AM, HoM, DM, RM)	0.015, 0.074, -0.024, 0.090	0.060, 0.117, 0.073, 0.089	0.24, 0.63, -0.32, 1.01	0.813, 0.538, 0.752, 0.336	-0.118, -0.183, -0.185, -0.107	0.147, 0.331, 0.137, 0.286

SE, standard error; CI, confidence interval; UL, upper limit; LL, lower limit; AM, allele model; HoM, homozygous model; HeM, heterozygous model; DM, dominant model; RM, recessive model; IL-10, interleukin 10.

Sensitivity analysis

Sensitivity analysis was performed by sequentially excluding individual studies, including studies which was not in agreement with HWE. Statistically similar results were obtained in all genetic models after sequentially excluding each study, indicating the stability of our data.

Publication bias

Begg's funnel plot and Egger's test were performed to assess the publication bias of included studies. The shapes of the funnel plots did not reveal any evidence of obvious asymmetry in the all genetic models. In all genetic models, Egger's test also did not show any significant statistical evidence of publication bias, indicating low risk of publication bias in this meta-analysis (Fig. 4, Table 6).

Fig. 4

Funnel plot for publication bias of the meta-analysis of tuberculosis risk and IL-10 polymorphisms in allele genetic model comparison. (A) IL-10 -1082G/A polymorphism. (B) IL-10 -819C/T polymorphism. (C) IL-10 -592A/C polymorphism. (D) IL-6 -174G/C polymorphism. IL-10, interleukin 10; IL-6, interleukin 6.

Table 6

Publication Bias of IL-10 -1082G/A, IL-10 -819C/T, and IL-10 -592A/C Polymorphisms in all Genetic Models

Polymorphisms	ZBegg's	PBegg's	tEgger's	PEgger's
IL-10-1082G/A (AM, HoM, HeM, DM, RM)	0.93, 0.47, 1.01, 1.28, 0.35	0.355, 0.637, 0.311, 0.201, 0.726	0.60, 0.79, 0.82, 0.95, 0.21	0.555, 0.436, 0.418, 0.352. 0.839
IL-10-819C/T (AM, HoM, HeM, DM, RM)	0.99, 0.10, 1.88, 1.78, 0.99	0.322, 0.921, 0.060, 0.075, 0.322	1.04, 0.80, 1.30, 1.28, -0.68	0.317, 0.438, 0.217, 0.221, 0.511
IL-10-592A/C (AM, HoM, HeM, DM, RM)	0.23, 0.32, 1.22, 1.31, 0.59	0.822, 0.753, 0.224, 0.192, 0.558	0.59, 0.57, 0.90, 1.36, -0.68	0.564, 0.575, 0.385, 0.195, 0.505
IL-6-174G/C (AM, HoM, HeM, DM, RM)	0.30, 0.75, 0.90, 0.00, 0.38	0.764, 0.452, 0.368, 1.000, 0.707	0.57, -0.09, 0.57, 0.51, 0.07	0.596, 0.934, 0.592, 0.634, 0.945

AM, allele model; HoM, homozygous model; HeM, heterozygous model; DM, dominant model; RM, recessive model; IL-10, interleukin 10; IL-6, interleukin 6.

DISCUSSION

This is not the first meta-analysis to assess the associations between three polymorphisms (-1082G/A, -819C/T, and -592A/C) in the IL-10 gene promoter and the risk of TB. We found that the results of our meta-analysis are inconsistent with a recent study of Liang, et al.39 in which some following shortcomings were found : 1) the NOS scores of 3 Chinese articles included were lower than 7 stars through quality assessment, 2) two studies that meet the inclusion criterion were excluded (Ma, et al.,28 Spinassé, et al.32), 3) the choice of genetic models was incorrect, 4) heterogeneity analysis and sensitivity analysis were missing, and 5) some extracted data was not accurate enough. Therefore, we performed this meta-analysis to examine the association between three IL-10 and IL-6 polymorphisms and TB risk again. Our meta-analysis results indicated that the presence of the IL-10 -1082G/A, -819C/T, and -592A/C polymorphisms was not associated with the risk of TB in all genetic models. On the other hand, the IL-6 -174G/C polymorphism might be associated with an decreased risk of TB in some genetic models (C allele vs. G allele: OR=0.77, 95% CI=0.64-0.91, p=0.003; CC vs. GG: OR=0.72, 95% CI=0.57-0.90, p=0.005; CC+CG vs. GG: OR=0.71, 95% CI=0.57-0.88, p=0.002).

We also carried out subgroup analysis based on ethnicity, sample types and control source in consideration of obvious heterogeneity. In the stratiied analysis by ethnicity, we observed significantly increased TB risk associated with the IL-10 -1082G/A polymorphism in recessive model in Europeans, IL-10 -819C/T polymorphism in Asians in heterozygous model and dominant model, IL-10 -592A/C polymorphism in Asians in Allele model, homozygous model and recessive model respectively, and a decreased TB risk associated with IL-6 -174G/C polymorphism was found in allele model, heterozygous model and dominant model in Asians. Different genetic background and environmental exposures might contribute to this ethnic difference. Subgroup analysis based on sample types suggested that IL-10 -1082G/A polymorphism may be related with an increased risk of TB in homozygous model in the PTB+EPTB mixed sample. The results of subgroup analysis by control source revealed no signiicant association with TB susceptibility among IL-10 and IL-6 polymorphisms.

In our meta-analysis, obvious heterogeneity was observed for IL-10 -1082G/A polymorphism in all genetic models, -819C/T polymorphism in heterozygous model and dominant model, and -592A/C polymorphism in all genetic models except for heterozygous model, whereas there was no obvious heterogeneity for IL-6 -174G/C polymorphism. Then, we used the Galbraith plots to explore the sources of heterogeneity. We found that all the I2 values were less than 50% and Pheterogeneity were greater than 0.1 after excluding some studies, thus indicating that these studies might be the major source of the heterogeneity for the IL-10 -1082G/A, -819C/T, and -592A/C polymorphisms. Owing to the limited number of studies in this meta-analysis, we restricted meta-regression analysis to four factors (sample types, ethnicity, control source, and genotyping method), which are the most likely to cause the heterogeneity between studies. Although the four above-mentioned factors had no significant impact on the heterogeneity except sample types factor for IL-10 -1082G/A in homozygous model, the results of subgroup analyses revealed that the ethnicity and sample type might contribute to the potential heterogeneity.

Some limitations of this meta-analysis exist which should be considered when interpreting the present results. Firstly, heterogeneity is a potential problem when interpreting the results of meta-analysis. Significant heterogeneity existed among some comparisons, especially for IL-10 -1082G/A and -592A/C polymorphisms. Secondly, this meta-analysis included the only published studies and publication bias may occur, although our results of publication bias showed no significance. Thirdly, host genetic susceptibility, environment factors and other factors might contribute to the pathogenesis of TB. Although many other factors such as age or gender may play a profound role in the development of TB, we did not make subgroup analysis based on these factors as data is not sufficient. Finally, some genetic polymorphisms of studies deviant from HWE were included in this meta-analysis, which suggested that there was potential bias during control selection or genotyping errors.

In conclusion, our meta-analysis suggested that IL-10 -1082G/A, -819C/T, and -592A/C polymorphisms had no association with TB risk in general population, while the IL-6 -174G/C polymorphism was signiicantly associated with decreased risk of TB in all genetic models except for recessive model. In the subgroup analysis, IL-10 -1082G/A polymorphism was associated with TB risk in Europeans in recessive model, and IL-10 -592A/C polymorphisms were significantly associated with TB risk in Asians in Allele model, homozygous model and recessive model, respectively, and a decreased TB risk associated with IL-6 -174G/C polymorphism was found in allele model, heterozygous model and dominant model in Asians. Furthermore, IL-10 -1082G/A polymorphism was associated also with an increased risk of TB in homozygous model in the PTB+EPTB mixed sample. However, additional well-designed and larger scale primary studies in populations with different ethnicities are required to further evaluate the IL-10 and IL-6 gene polymorphisms with TB risk in future.