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Int J STD AIDS OnlineFirst, published on December 12, 2014 as doi:10.1177/0956462414563627
Original research article
Interferon-gamma gene polymorphism influences the frequency of a Chlamydia trachomatis cervical infection in young women
International Journal of STD & AIDS 0(0) 1–5 ! The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0956462414563627 std.sagepub.com
Jose´ Eleute´rio Jr1, Rosiane A Teles2, Iara M Linhares3,4, Neil Normand4 and Steven S Witkin4
Summary Introduction: Cervicitis associated with Chlamydia trachomatis is frequent worldwide, but the factors determining susceptibility to infection remain incompletely determined. Objective: We evaluated whether a functional single nucleotide polymorphism at position þ874 in the gene coding for interferon gamma (rs2430561) influenced the likelihood of having a cervical C. trachomatis infection. Methods: This was a cross-sectional study of 142 sexually active women attending a general gynaecology service on the outskirts of the city of Fortaleza in northeastern Brazil between August 2011 and August 2012. Endocervical swabs were evaluated for C. trachomatis DNA using hybrid capture. DNA from buccal swabs was utilised for detection of the interferon gamma 874 T/A single nucleotide polymorphism by gene amplification, endonuclease digestion and gel electrophoresis. Associations were analysed by Fisher’s exact test. Odds ratios and 95% confidence intervals were determined. Results: Nineteen women (13.4%) were positive for C. trachomatis in their cervix. Positivity was 21.7% in women with the A,A genotype versus 7.0% in women with one or two T alleles (p ¼ 0.0227). The variant T allele frequency, associated with elevated interferon gamma production, was 36.2% in women who were negative for C. trachomatis as opposed to 18.4% in women who were positive for a cervical infection with this organism (p ¼ 0.0415). Conclusion: Possession of the T allele at position þ874 in the gene coding for interferon gamma is associated with a reduced likelihood of a C. trachomatis cervical infection.
Keywords Chlamydia trachomatis, cervical infection, interferon gamma, gene polymorphism Date received: 31 July 2014; revised: 13th November 2014; accepted: 14 November 2014
Introduction Several studies have detailed a high prevalence of Chlamydia trachomatis female genital tract infections worldwide.1 For South America, the prevalence of a C. trachomatis infection in women has been reported to be 26.4% in Argentina,2 7.6% in Peru,3 4.7–6.9% in Chile4,5 and between 6.1 and 23.9% in Brazil.6–8 Known risk factors associated with C. trachomatis cervical infection are early age of sexual debut, having multiple sex partners and young age.3,9 Studies on the immune response, primarily in laboratory animals have identified interferon gamma (IFN-g) as a key component in the host defence against a C. trachomatis infection.10,11 Specifically, CD4þ helper T lymphocytes
1
Departamento de Sau´de Maternoinfantil, Faculdade de Medicina, Universidade Federal do Ceara´, Fortaleza, Brazil 2 Mestrado em Patologia, Faculdade de Medicina, Universidade Federal do Ceara´, Fortaleza, Brazil 3 Departamento de Obstetricia e Ginecologia, Faculdade de Medicina, Universidade de Sa˜o Paulo, Sa˜o Paulo, Brazil 4 Department of Obstetrics and Gynecology, Weill Cornell Medical College, New York, NY, USA Corresponding author: Jose´ Eleute´rio Jr, Departamento de Sau´de Maternoinfantil, Faculdade de Medicina, Universidade Federal do Ceara´, Rua: Prof. Costa Mendes, 1608 - 2 Andar, 60.430-140 Fortaleza, Brazil. Email: [email protected]
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secreted IFN-g in response to C. trachomatis and controlled the infection.12 Another possible source of IFN-g in the genital tract may be from neutrophils.13 Similarly, chlamydial infection was enhanced by addition of antibodies to IFN-g and resolved by administration of exogenous IFN-g14 This Th1-directed IFNg-producing response can limit a Chlamydia infection by enhancing the phagocytic potential of macrophages and their ability to present processed chlamydial antigens to T lymphocytes in the induction of a cellmediated immune response. IFN-g may also directly inhibit the replication of C. trachomatis within infected cells by modifying the activity of indoleamine 2,3-dioxygenase 1 (IDO1) and nitric oxide synthase and the expression of transferrin receptors.15 C. trachomatis cannot synthesise tryptophan, and so this amino acid must be supplied by the infected host cell. IDO1 is induced by IFN-g and catabolises tryptophan.16,17 Genetic variability has also been shown to influence susceptibility and/or the consequences of a C. trachomatis infection. Single nucleotide polymorphisms (SNPs) in the genes coding for mannose-binding lectin,18 interleukin-10,19 interleukin-12,20 tumour necrosis factor alpha,21 HLA-DR antigens22 and Tolllike receptors23,24 have all been associated with an altered chlamydial response. Given the central role of IFN-g in combatting a chlamydial infection, we evaluated whether a functional SNP at position þ874 in the IFNG gene (rs2430561) that codes for IFN-g influences susceptibility to a chlamydial cervical infection. The variant T allele at this locus has been associated with enhanced IFN-g production in comparison to carriage of the wild type A allele.25
transported to the Department of Obstetrics and Gynecology at Weill Cornell Medical College in New York City. The T/A IFNG polymorphism at position þ874 was determined by gene amplification, endonuclease digestion and agarose gel electrophoresis, using a published protocol.26 The A allele yielded a single band at 176 base pairs while the T allele yielded two bands at 148 and 28 base pairs. Genotype and allele frequencies were determined by direct counting and then dividing by the number of chromosomes to obtain allele frequency and by the number of women to obtain genotype frequency. Goodness of fit to Hardy–Weinberg equilibrium was determined by comparing the expected genotype frequencies with the observed values, using the Chi square test. Associations between genotype or allele and chlamydial infection were analysed by Fisher’s exact test. Odds ratios and 95% confidence intervals (CI) were calculated for each comparison. A p value 0.05).
Discussion The þ874 IFNG gene polymorphism has previously been reported to be associated in Brazilian populations with decreased susceptibility to tuberculosis27 and leprosy.28 We can now also add C. trachomatis cervical infection to this list. It thus appears that an individual’s IFNG genotype is one factor that determines the extent of their immune response, and thus their likelihood of becoming infected, by several intracellular bacterial pathogens. In contrast to our results, Ohman et al.21 did not observe a significant association between the IFN-g þ874 polymorphism and chlamydial tubal infertility. However, in their study women with severe tubal damage were, in fact, more likely to be positive for the AA genotype. This suggests that perhaps with a larger sample size their observed difference would have reached statistical significance. Alternatively, the
Table 2. Interferon-g gene polymorphism in women with a Chlamydia trachomatis infection. No. (%) positive Genotype Ct– A,A A,T T,T
Allele frequency (%)
Ctþ
Allele Ct–
47 (38.2) 13 (68.4) 63 (51.2) 5 (26.3) 13 (10.6) 1 (5.3)
Ctþ
a
A T
157 (63.8) 31 (81.6) 89 (36.2)b 7 (18.4)
a p ¼ 0.0227 (A,A versus A,T plus T,T), Odds ratio (OR) ¼ 3.504, 95% confidence interval (CI) ¼ 1.246, 9.850. b p ¼ 0.0415 (Ct- versus Ctþ), OR ¼ 2.510, 95% CI ¼ 1.062, 5.906.
severity of a chlamydial infection in the fallopian tubes may be less dependent on an IFN-g-mediated immune response than in an initial cervical chlamydial infection. Another possibility might be that detection of C. trachomatis by DNA analysis may not always correlate with the presence of viable organisms.29 Further evaluations of women with chlamydial-related and chlamydia-independent fallopian tube infections are needed to resolve this issue. IFN-g as been shown to be important in the cellmediated immune defence against a C. trachomatis infection in animals. Similarly, studies in experimental animals and chlamydial-infected cell lines have demonstrated that addition of low levels of IFN-g promoted the transformation of this organism into a metabolically inactive persistent state30 capable of evading immune defence mechanisms.31 In this form, many chlamydial genes associated with cell division were silent, while genes coding for proteins involved in tryptophan utilisation, biosynthesis of phospholipids and DNA repair remained active.32 In addition, there was a marked up-regulation of chlamydial 60 kDa heat shock protein (hsp60) production and this protein was released into the extracellular milieu. The subsequent host immune response to chlamydial hsp60 results in induction of inflammation and damage to the fallopian tubes. Scarring of the fallopian tubes leads to infertility or risk of ectopic pregnancy.31 In addition, it has been shown that individual strains of C. trachomatis differ in their sensitivity to IFN-gmediated inhibition,33 and antibiotic treatment to augment IFN-g-mediated chlamydial killing may vary in efficacy under different conditions.34 C. trachomatis in the genital tract, but not ocular C. trachomatis infections, is also capable of bypassing IFN-g-induced tryptophan depletion by synthesising this amino acid from indole. Indole is produced by bacteria associated with bacterial vaginosis, an alteration of the vaginal microbiota, as well as by a parasitic Trichomonas vaginalis infection.35 Thus, in women with a ‘silent’ persistent chlamydial infection, the subsequent acquisition of a genital tract infection can lead to reactivation of a productive chlamydial infection. The genetically determined extent of IFN-g production may possibly also influence the likelihood of alterations in the composition of the genital tract microbiota that can influence susceptibility to chlamydial acquisition.36 Definitive evidence of the precise role(s) of IFN-g in chlamydial perpetuation and/or anti-chlamydial immune defence in humans is still lacking. Based on the present study it is reasonable to assume that women who are homozygous carriers of the IFNG A allele and therefore relatively low producers of IFN-g may be at increased risk for development of adverse sequelae following an initial chlamydial infection in
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the genital tract and possibly also at other body sites. Limitations of the present study are that most Brazilians are of mixed ethnicity and so possible ethnic or racial variations of this polymorphism with susceptibility remain to be determined. However, we did not see a variation in genotypes between women self-identified as white or non-white. Furthermore, we did not assess previous history of exposure to C. trachomatis and although all women in the study were sexually active we cannot verify that all were in fact exposed to C. trachomatis. However, the C. trachomatis-positive women did not differ from the negative women in frequency of sexual intercourse or number of sexual partners. Verification of the results in the present study may eventually lead to development of protocols to determine an infected woman’s IFNG genotype and relate her time interval between STD screenings as well as her antibiotic regimen if infected to the genetic findings. Development of individualbased evaluation and treatment protocols may eventually reduce the occurrence of chlamydial-mediated sequela such as ectopic pregnancy or tubal infertility. Declaration of Conflicting Interests The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The authors received no financial support for the research, authorship, and/or publication of this article.
References 1. WHO. Sexually transmitted infections: issues in adolescent health and development. Geneva: World Health Organization (WHO), 2004. 2. Deluca DG, Basiletti J, Schlover E, et al. Chlamydia trachomatis as a probable cofactor in human papillomavirus infection in aboriginal women from northeastern Argentina. Braz J Infect Dis 2011; 15: 567–572. 3. Paul KJ, Garcia PJ, Giesel AE, et al. Generation C: prevalence of and risk factors for Chlamydia trachomatis among adolescents and Young women in Lima, Peru. J Womens Health 2009; 18: 1419–1424. 4. Martinez TMA, Reid SI, Arias C, et al. Prevalence of cervical infection by Chlamydia trachomatis among Chilean women living in the Metropolitan Region. Rev Med Chil 2008; 136: 1294–1300. 5. Huneeus A, Pumarino MG, Schilling A, et al. Prevalencia de Chlamydia trachomatis y Neisseria gonorrhoeae en adolescents chilenas. Rev Med Chil 2009; 137: 1569–1574. 6. Eleute´rio RMN, Eleute´rio J Jr, Giraldo PC, et al. Cervicite por Chlamydia trachomatis em mulheres sexualmente ativas atendidas em um servic¸o privado de ginecologia na cidade de Fortaleza. Rev Bras Anal Clin 2007; 39: 287–290.
7. Jalil EM, Pinto VM, Benzaken AS, et al. Prevalence of Chlamydia and Neisseria gonorrhoeae infections in pregnant women in six Brazilian cities. Rev Bras Ginecol Obstet 2008; 30: 614–698. 8. Marconi C, Donders GGG, Martin LF, et al. Chlamydial infection in a high risk population: association with vaginal flora patterns. Arch Gynecol Obstet 2012; 285: 1013–1018. 9. Bearinger LH, Sieving RE, Ferguson J, et al. Global perspectives on the sexual and reproductive health of adolescents: patterns, prevention, and potential. Lancet 2007; 369: 1220–1231. 10. Roshick C, Wood H, Caldwell HD, et al. Comparison of gamma interferon-mediated antichlamydial defense mechanisms in human and mouse cells. Infect Immun 2006; 74: 225–238. 11. Ito JI and Lyons JM. Role of gamma interferon in controlling mouse chlamydial genital tract infections. Infect Immun 1999; 67: 5518–5521. 12. Su H and Caldwell HD. CD4þ T cells play a significant role in adoptive immunity to Chlamydia trachomatis infection of the mouse genital tract. Infect Immun 1995; 63: 3302–3308. 13. Yeaman GR, Collins JE, Currie JK, et al. IFN-g is produced by polymorphonuclear neutrophils in human uterine endometrium and by cultured peripheral blood polymorphonuclear neutrophils. J Immunol 1998; 160: 5145–5153. 14. Rank RG, Ramsey KH, Park EA, et al. Effect of gamma interferon on resolution of murine schlamydial genital infection. Infect Immun 1992; 60: 4427–4429. 15. Loomis WP and Starnbach MNT. T Cell responses to Chlamydia trachomatis. Curr Opin Microbiol 2002; 5: 87–91. 16. Shemer Y and Sarov I. Inhibition of growth of Chlamydia trachomatis by human gamma interferon. Infect Immun 1985; 48: 592–596. 17. Byrne GI, Lehmann LK and Landry GJ. Induction of tryptophan catabolism is the mechanism for gammainterferon-mediated inhibition of intracellular Chlamydia psittaci replication in T24 cells. Infect Immun 1986; 53: 347–351. 18. Sziller I, Babula O, Ujhazy A, et al. Chlamydia trachomatis infection, fallopian tube damage and a mannosebinding lectin codon 54 gene polymorphism. Hum Reprod 2007; 22: 1861–1865. 19. Ohman H, Tiitinen A, Halttunen M, et al. IL-10 polymorphism and cell-mediated immune response to Chlamydia trachomatis. Genes Immun 2006; 7: 243–249. 20. Ohman H, Bailey R, Natividad A, et al. Effect of IL12A and IL12B polymorphisms on the risk of Chlamydia trachomatis-induced tubal factor infertility and disease severity. Hum Reprod 2012; 27: 2217–2223. 21. Ohman H, Tiitinen A, Haittunen M, et al. Cytokine polymorphisms and severity of tubal damage in women with Chlamydia-associated infertility. J Infect Dis 2009; 199: 1353–1359. 22. Cohen CR, Gichui J, Rukaria R, et al. Immunogenetic correlates for Chlamydia trachomatis-associated tubal infertility. Obstet Gynecol 2003; 101: 438–444.
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23. Taylor BD, Darville T, Ferrell RE, et al. Variants in tolllike receptor 1 and 4 genes are associated with Chlamydia trachomatis among women with pelvic inflammatory disease. J Infect Dis 2012; 205: 603–609. 24. Karimi O, Ouburg S, de Vries HJ, et al. TLR2 haplotypes in the susceptibility to and severity of Chlamydia trachomatis infections in Dutch women. Drugs Today 2009; 45: 67–74. 25. Pravica V, Perrey C, Stevens A, et al. A single nucleotide polymorphism in the first intron of the human IFNgamma gene: absolute correlation with a polymorphic CA microsatellite marker of high IFN-gamma production. Human Immunol 2000; 61: 863–866. 26. Ben Selma W, Harizi H, Bougmiza I, et al. Interferon gamma þ874T/A polymorphism is associated with susceptibility to active pulmonary tuberculosis development in Tunisian patients. DNA Cell Biol 2011; 30: 379–387. 27. Amim LH, Pacheco AG, Fonseca-Costa J, et al. Role of IFN-gamma þ874 T/A single nucleotide polymorphism in the tuberculosis outcome among Brazilian subjects. Mol Biol Rep 2008; 35: 563–566. 28. Cardoso CC, Pereira AC, Brito-de-Souza VN, et al. IFNG þ874 T>A single nucleotide polymorphism is associated with leprosy among Brazilians. Hum Genet 2010; 128: 481–490. 29. Lewis ME, Belland RJ, AbdelRahman YM, et al. Morphologic and molecular evolution of Chlamydia trachomatis growth in human endocervix reveals distinct
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growth patterns. Frontiers Cell Infect Microbiol 2014; 4: 71. DOI: 10.3389/fcimb.2014.00071. eCollection 2014. Beatty WI, Morrison RP and Byrne GI. Persistent chlamydiae: from cell culture to a paradigm for chlamydial pathogenesis. Microbiol Rev 1994; 58: 686–699. Linhares IM and Witkin SS. Immunopathogenic consequences of Chlamydia trachomatis 60 kDa heat shock protein expression in the female reproductive tract. Cell Stress Chaperones 2010; 15: 467–473. Belland RI, Nelson DE, Virok D, et al. Transcriptome analysis of chlamydial growth during IFN-gammamediated persistence and reactivation. Proc Natl Acad Sci USA 2003; 100: 15971–15976. Morrison RP. Differential sensitivities of Chlamydia trachomatis strains to inhibitory effects of gamma interferon. Infect Immun 2000; 68: 6038–6040. Shima K, Klinger M, Solbach W, et al. Activities of firstchoice antimicrobials against gamma interferon-treated Chlamydia trachomatis differ in hypoxia. Antimicrob Agents Chemother 2013; 57: 2828–2830. Caldwell HD, Wood H, Crane D, et al. Polymorphisms in Chlamydia trachomatis tryptophan synthase genes differentiate between genital and ocular isolates. J Clin Invest 2003; 111: 1757–1769. Aiyar A, Quayle AJ, Buckner LR, et al. Influence of the tryptophan-indole-IFNg axis on human genital Chlamydia trachomatis infection: role of vaginal co-infections. Frontiers Cell Infect Microbiol 2014; 4: 72. DOI: 10.3389/fcimb.2014.00072. eCollection 2014.
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Int J STD AIDS OnlineFirst, published on December 12, 2014 as doi:10.1177/0956462414563627
Original research article
Interferon-gamma gene polymorphism influences the frequency of a Chlamydia trachomatis cervical infection in young women
International Journal of STD & AIDS 0(0) 1–5 ! The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0956462414563627 std.sagepub.com
Jose´ Eleute´rio Jr1, Rosiane A Teles2, Iara M Linhares3,4, Neil Normand4 and Steven S Witkin4
Summary Introduction: Cervicitis associated with Chlamydia trachomatis is frequent worldwide, but the factors determining susceptibility to infection remain incompletely determined. Objective: We evaluated whether a functional single nucleotide polymorphism at position þ874 in the gene coding for interferon gamma (rs2430561) influenced the likelihood of having a cervical C. trachomatis infection. Methods: This was a cross-sectional study of 142 sexually active women attending a general gynaecology service on the outskirts of the city of Fortaleza in northeastern Brazil between August 2011 and August 2012. Endocervical swabs were evaluated for C. trachomatis DNA using hybrid capture. DNA from buccal swabs was utilised for detection of the interferon gamma 874 T/A single nucleotide polymorphism by gene amplification, endonuclease digestion and gel electrophoresis. Associations were analysed by Fisher’s exact test. Odds ratios and 95% confidence intervals were determined. Results: Nineteen women (13.4%) were positive for C. trachomatis in their cervix. Positivity was 21.7% in women with the A,A genotype versus 7.0% in women with one or two T alleles (p ¼ 0.0227). The variant T allele frequency, associated with elevated interferon gamma production, was 36.2% in women who were negative for C. trachomatis as opposed to 18.4% in women who were positive for a cervical infection with this organism (p ¼ 0.0415). Conclusion: Possession of the T allele at position þ874 in the gene coding for interferon gamma is associated with a reduced likelihood of a C. trachomatis cervical infection.
Keywords Chlamydia trachomatis, cervical infection, interferon gamma, gene polymorphism Date received: 31 July 2014; revised: 13th November 2014; accepted: 14 November 2014
Introduction Several studies have detailed a high prevalence of Chlamydia trachomatis female genital tract infections worldwide.1 For South America, the prevalence of a C. trachomatis infection in women has been reported to be 26.4% in Argentina,2 7.6% in Peru,3 4.7–6.9% in Chile4,5 and between 6.1 and 23.9% in Brazil.6–8 Known risk factors associated with C. trachomatis cervical infection are early age of sexual debut, having multiple sex partners and young age.3,9 Studies on the immune response, primarily in laboratory animals have identified interferon gamma (IFN-g) as a key component in the host defence against a C. trachomatis infection.10,11 Specifically, CD4þ helper T lymphocytes
1
Departamento de Sau´de Maternoinfantil, Faculdade de Medicina, Universidade Federal do Ceara´, Fortaleza, Brazil 2 Mestrado em Patologia, Faculdade de Medicina, Universidade Federal do Ceara´, Fortaleza, Brazil 3 Departamento de Obstetricia e Ginecologia, Faculdade de Medicina, Universidade de Sa˜o Paulo, Sa˜o Paulo, Brazil 4 Department of Obstetrics and Gynecology, Weill Cornell Medical College, New York, NY, USA Corresponding author: Jose´ Eleute´rio Jr, Departamento de Sau´de Maternoinfantil, Faculdade de Medicina, Universidade Federal do Ceara´, Rua: Prof. Costa Mendes, 1608 - 2 Andar, 60.430-140 Fortaleza, Brazil. Email: [email protected]
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secreted IFN-g in response to C. trachomatis and controlled the infection.12 Another possible source of IFN-g in the genital tract may be from neutrophils.13 Similarly, chlamydial infection was enhanced by addition of antibodies to IFN-g and resolved by administration of exogenous IFN-g14 This Th1-directed IFNg-producing response can limit a Chlamydia infection by enhancing the phagocytic potential of macrophages and their ability to present processed chlamydial antigens to T lymphocytes in the induction of a cellmediated immune response. IFN-g may also directly inhibit the replication of C. trachomatis within infected cells by modifying the activity of indoleamine 2,3-dioxygenase 1 (IDO1) and nitric oxide synthase and the expression of transferrin receptors.15 C. trachomatis cannot synthesise tryptophan, and so this amino acid must be supplied by the infected host cell. IDO1 is induced by IFN-g and catabolises tryptophan.16,17 Genetic variability has also been shown to influence susceptibility and/or the consequences of a C. trachomatis infection. Single nucleotide polymorphisms (SNPs) in the genes coding for mannose-binding lectin,18 interleukin-10,19 interleukin-12,20 tumour necrosis factor alpha,21 HLA-DR antigens22 and Tolllike receptors23,24 have all been associated with an altered chlamydial response. Given the central role of IFN-g in combatting a chlamydial infection, we evaluated whether a functional SNP at position þ874 in the IFNG gene (rs2430561) that codes for IFN-g influences susceptibility to a chlamydial cervical infection. The variant T allele at this locus has been associated with enhanced IFN-g production in comparison to carriage of the wild type A allele.25
transported to the Department of Obstetrics and Gynecology at Weill Cornell Medical College in New York City. The T/A IFNG polymorphism at position þ874 was determined by gene amplification, endonuclease digestion and agarose gel electrophoresis, using a published protocol.26 The A allele yielded a single band at 176 base pairs while the T allele yielded two bands at 148 and 28 base pairs. Genotype and allele frequencies were determined by direct counting and then dividing by the number of chromosomes to obtain allele frequency and by the number of women to obtain genotype frequency. Goodness of fit to Hardy–Weinberg equilibrium was determined by comparing the expected genotype frequencies with the observed values, using the Chi square test. Associations between genotype or allele and chlamydial infection were analysed by Fisher’s exact test. Odds ratios and 95% confidence intervals (CI) were calculated for each comparison. A p value 0.05).
Discussion The þ874 IFNG gene polymorphism has previously been reported to be associated in Brazilian populations with decreased susceptibility to tuberculosis27 and leprosy.28 We can now also add C. trachomatis cervical infection to this list. It thus appears that an individual’s IFNG genotype is one factor that determines the extent of their immune response, and thus their likelihood of becoming infected, by several intracellular bacterial pathogens. In contrast to our results, Ohman et al.21 did not observe a significant association between the IFN-g þ874 polymorphism and chlamydial tubal infertility. However, in their study women with severe tubal damage were, in fact, more likely to be positive for the AA genotype. This suggests that perhaps with a larger sample size their observed difference would have reached statistical significance. Alternatively, the
Table 2. Interferon-g gene polymorphism in women with a Chlamydia trachomatis infection. No. (%) positive Genotype Ct– A,A A,T T,T
Allele frequency (%)
Ctþ
Allele Ct–
47 (38.2) 13 (68.4) 63 (51.2) 5 (26.3) 13 (10.6) 1 (5.3)
Ctþ
a
A T
157 (63.8) 31 (81.6) 89 (36.2)b 7 (18.4)
a p ¼ 0.0227 (A,A versus A,T plus T,T), Odds ratio (OR) ¼ 3.504, 95% confidence interval (CI) ¼ 1.246, 9.850. b p ¼ 0.0415 (Ct- versus Ctþ), OR ¼ 2.510, 95% CI ¼ 1.062, 5.906.
severity of a chlamydial infection in the fallopian tubes may be less dependent on an IFN-g-mediated immune response than in an initial cervical chlamydial infection. Another possibility might be that detection of C. trachomatis by DNA analysis may not always correlate with the presence of viable organisms.29 Further evaluations of women with chlamydial-related and chlamydia-independent fallopian tube infections are needed to resolve this issue. IFN-g as been shown to be important in the cellmediated immune defence against a C. trachomatis infection in animals. Similarly, studies in experimental animals and chlamydial-infected cell lines have demonstrated that addition of low levels of IFN-g promoted the transformation of this organism into a metabolically inactive persistent state30 capable of evading immune defence mechanisms.31 In this form, many chlamydial genes associated with cell division were silent, while genes coding for proteins involved in tryptophan utilisation, biosynthesis of phospholipids and DNA repair remained active.32 In addition, there was a marked up-regulation of chlamydial 60 kDa heat shock protein (hsp60) production and this protein was released into the extracellular milieu. The subsequent host immune response to chlamydial hsp60 results in induction of inflammation and damage to the fallopian tubes. Scarring of the fallopian tubes leads to infertility or risk of ectopic pregnancy.31 In addition, it has been shown that individual strains of C. trachomatis differ in their sensitivity to IFN-gmediated inhibition,33 and antibiotic treatment to augment IFN-g-mediated chlamydial killing may vary in efficacy under different conditions.34 C. trachomatis in the genital tract, but not ocular C. trachomatis infections, is also capable of bypassing IFN-g-induced tryptophan depletion by synthesising this amino acid from indole. Indole is produced by bacteria associated with bacterial vaginosis, an alteration of the vaginal microbiota, as well as by a parasitic Trichomonas vaginalis infection.35 Thus, in women with a ‘silent’ persistent chlamydial infection, the subsequent acquisition of a genital tract infection can lead to reactivation of a productive chlamydial infection. The genetically determined extent of IFN-g production may possibly also influence the likelihood of alterations in the composition of the genital tract microbiota that can influence susceptibility to chlamydial acquisition.36 Definitive evidence of the precise role(s) of IFN-g in chlamydial perpetuation and/or anti-chlamydial immune defence in humans is still lacking. Based on the present study it is reasonable to assume that women who are homozygous carriers of the IFNG A allele and therefore relatively low producers of IFN-g may be at increased risk for development of adverse sequelae following an initial chlamydial infection in
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the genital tract and possibly also at other body sites. Limitations of the present study are that most Brazilians are of mixed ethnicity and so possible ethnic or racial variations of this polymorphism with susceptibility remain to be determined. However, we did not see a variation in genotypes between women self-identified as white or non-white. Furthermore, we did not assess previous history of exposure to C. trachomatis and although all women in the study were sexually active we cannot verify that all were in fact exposed to C. trachomatis. However, the C. trachomatis-positive women did not differ from the negative women in frequency of sexual intercourse or number of sexual partners. Verification of the results in the present study may eventually lead to development of protocols to determine an infected woman’s IFNG genotype and relate her time interval between STD screenings as well as her antibiotic regimen if infected to the genetic findings. Development of individualbased evaluation and treatment protocols may eventually reduce the occurrence of chlamydial-mediated sequela such as ectopic pregnancy or tubal infertility. Declaration of Conflicting Interests The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding The authors received no financial support for the research, authorship, and/or publication of this article.
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