Analysis of polymorphisms, gene expression and serum levels of IL-18, IFN-y and IL18BP in chronic HCV infection and spontaneous clearance

Author(s)

Paola Lara Faria

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina (FM/SBD)
• Defense date: 2015-02-02

Examining board members

João Renato Rebello Pinho; Celso Francisco Hernandes Granato; Luciana Bertocco de Paiva Haddad

• Advisor: João Renato Rebello Pinho

Abstract

The course of HCV infection is determined by the competence of the innate and adaptive immune response of the host. IL-18 is an important proinflammatory cytokine in both immune responses and acts synergistically with IL-12 induces the expression of IFN-y by T and natural killer cells. The IFN-yturn plays a key role in fighting intracellular infections, inducing an antiviral state in infected cells. The balance of IL-18 is controlled by IL18BP, an important cytokine that acts as a natural antagonist. Studies show that individuals chronically infected with HCV have elevated serum levels of IL-18 and IL18BP. Therefore, this study aimed to: 1) determine the genotype of single nucleotide polymorphisms (SNPs) located in genes of IL-18 (-607 C > A and -137 G > C), IL18BP (rs2298455 and rs1541304) and IFN-y +874 T > A; 2) to quantify the expression of their respective mRNAs; and finally 3) the determination of serum levels of the respective cytokines. Fifty-one individuals with spontaneous clearance and 50 were selected with chronic HCV genotype 1 infection who underwent the technique of real-time PCR for genotyping polymorphisms of IL-18 (-607 C > A and -137 G > C), IL18BP (rs2298455 and rs1541304) and IFN-y +874 T > A; later analysis of gene expression of these mRNA was performed using GAPDH as endogenous control and used the ELISA method for the serum of these cytokines. The distribution of genotypes in the IL-18 polymorphisms and IL18BP genes were similar in both study groups. However, for the polymorphism in the IFN-y gene, the genotype most frequently observed in the group of TA chronic infection, whereas in the group of spontaneous clearance AA was more frequent (p = 0.006) genotype. In contrast to gene expression allowed us to observe that in individuals with chronic infection the mRNA of IL-18 (p < 0.001) and IL18BP (p < 0.001) had a higher expression when compared with individuals with spontaneous resolution, and that this reflected in serum using the ELISA technique, where individuals chronically infected with HCV had higher serum levels of IL-18 (p < 0.001) and IL18BP (p = 0.012) than subjects with spontaneous clearance. The G allele was associated with increased production of IL-18 (P = 0.02)in spontaneous clearance group. Regarding the gene expression of IFN-y mRNA was not observed any difference between the groups (p = 0.322) and the serum was not detected in both groups. The results suggest that although the immune system is stimulated during HCV infection leads to viral persistence of anergy a state where the production of IFN-? appears to be scarce for an effective immune response, and the means in which modulate the expression the IFN-y gene still seem unclear, however have been described post-transcriptional mechanisms which target the 3\'UTR of the mRNA of IFN-y may interfere with its expression (AU)

• FAPESP's process: 12/20248-4 - Analysis of polymorphisms, gene expression and serum levels of IL-18,IL18BP and IFN-gamma in chronic HCV infection and spontaneous clearance
• Grantee: Paola Lara Faria
• Support Opportunities: Scholarships in Brazil - Master