Antiviral immune responses in OBI are continuously stimulated by persistent/intermittent low concentrations of HBV antigens and cytokines can play an important role in controlling HBV replication . In this present study, the levels of cytokines in OBI patients were heterogeneous, showing dissemination over a wide range of values with high standard deviations, which can be attributed to the different genotypes and a wide range of viral loads, however, due to the low number of samples, it was not possible to confirm this correlation between genotypes, viral load and the cytokines studied. In the present study, the prevalence of OBI in patients with CHC was 9.6%. Previous studies analyzing serum samples of Brazilian HCV infected patients found frequencies of OBI ranging from 0 to 24% [40-46].
OBI patients usually have a low viral load with suppression of HBV replication and thus, most OBI patients have normal liver histology or minimal fibrosis. However, they are still at risk of developing liver cirrhosis. The prevalence of OBI in cirrhotic patients varies widely from 4 to 38% between different regions of the world [22, 47].
The persistence of HBV DNA in hepatocytes triggers a constant immune response, inducing mild but continuous liver inflammation, which can accelerate liver damage and favor the development of liver cirrhosis in other chronic liver diseases, such as in patients with chronic hepatitis C [22, 48-50]. OBI can contribute to the development of HCC under direct and indirect mechanisms similar to those of chronic HBV infection .
In addition, the presence of OBI/HCV coinfection is believed to have an adverse effect on the response to treatment in IFN-based therapies . Coinfection with OBI/HCV was associated with decreased intrahepatic expression of interferon receptor mRNA (IFNAR2), higher levels of serum HCV RNA and a poor IFN response, regardless of the HCV genotype. These results suggest the possibility that coinfection is one of the factors that can lead to an unfavorable IFN response in chronic hepatitis C by negative regulation of the IFN receptor gene expression in the liver .
Levels of alanine aminotransferase (ALT) are generally slightly higher in occult hepatitis B in HCV co-infection, with averages ranging from 39–158 IU/mL [54, 55]. In our study we found a mean of 62.91 ALT IU/ml, but no correlation was found between the levels of ALT/AST at the age, viral load and the analyzed cytokines.
ALT levels correlate well with inflammatory activity on biopsy, which is generally mild . However, in contrast to this mild inflammation, most studies have shown an increased prevalence of fibrosis/advanced cirrhosis in patients with occult hepatitis B [56-58]. These findings corroborate those of the present study, in which 81.8% of OBI/HCV patients demonstrated stage F4 of fibrosis.
In our study, we found a significant increase in the median of IL-2 in occult patients when compared to healthy controls, other studies find overexpression of IL-2 exclusively in patients infected with OBI when compared to healthy individuals and patients who have resolved HBV infection  and in patients monoinfected with HCV . IL-2 plays an important role in the efficient development of effector cytotoxic CD8+ T cells, effector cells with a high expression of receptors for IL-2 (IL-2R) are cells that cause direct damage to the liver .
Unfortunately, in our study, was not possible to evaluate the cytokines levels in patients monoinfected with HCV. However, a study conducted by Baskic and collegues, 2017  investigating the cytokine profile in chronic hepatitis C demonstrated that median levels of IL-17A were lower in patients with HCV than in controls. In our study, low levels of IL-17A were also found in OBI/HCV coinfected patients. We found significant difference between OBI/HCV compared to monoinfected HBV group and healthy controls with higher means in the monoinfected patients with HBV. The roles of IL-17A in inducing appropriate immune responses against viral infections are controversial, IL-17 may play a positive role in antiviral immune responses in several diseases . However, for chronic hepatitis B, is well known, that IL-17A is positively regulated in HBV-mediated inflammation and may be relevant for the development of liver cirrhosis and HCC [36, 67, 68]. IL-17A can also significantly stimulate monocytes and DCs to express their ligand (IL-17R) and produce pro-inflammatory cytokines such as IL-1β, TNF-α, IL-6, etc., which are important for liver damage during progression of chronic hepatitis B .
Other cytokines possibly involved in OBI include increased interleukin 10 (IL-10), IL-10 can leads to reduced expression of IL-12, stromal cell-derived factor (SDF)-1α, and C-C chemokine receptor (CCR), which leads to the interruption of T and natural killer cells (NK cell) activation and the recruitment of immune cells to the infected liver . IL-10 production is also increased in monoinfected patients with chronic hepatitis C, the HCV RNA load is closely associated with IL-10 expressions, and inhibition of HCV replication was accompanied by a reduction in IL-10 [41,61]. Corroborating these findings, our study showed significantly higher means in IL-10 levels in patients with OBI/HCV compared with controls.
In vivo levels of IL-6 have been associated with plasma ALT levels and the degree of liver fibrosis in patients with HCC in HCV monoinfected patients  and a previous study demonstrated a low detection rate of IL-6 in patients infected with OBI when compared to healthy individuals and patients who resolved HBV infection . We found high levels of IL-6 in the occult group in our study and significant difference between OBI/HCV compared to monoinfected HBV group and healthy controls, this increase in IL-6 expression could be attributed to HCV co-infection, since several studies have already found that this cytokine is associated with HCV chronic infection [63, 72, 73].
It is well known that IL-6 can play two important roles in the pathogenesis of hepatitis B, can protect the liver from virus infections by stimulating immune responses against infected hepatocytes and can inhibit the HBV entry in hepatocytes up to 90% when cells are treated with IL-6 resulting in a marked reduction in cccDNA and HBsAg secretion . But the IL-6 can also play an important role in the induction of hepatitis, cirrhosis, and HCC [33, 75].
We found levels of IL-4 significantly increased in occult patients. IL-4 is a cytokine that can suppress the Th1-type response, maintaining persistent HBV replication and promoting immune tolerance [32, 76, 77]. Some studies show that patients with severe hepatitis C had higher levels of IL-4 compared to milder cases  and serum IL-4 levels were significantly increased in patients with chronic HCV .
Serum HBV DNA levels are typically low in occult hepatitis B, but despite the low rate of replication, detection of HBV DNA can be associated with ALT outbreaks that can be associated with advanced fibrosis/cirrhosis. In addition, occult OBI/HCV coinfection is associated with decreased response to interferon .
There were some limitations in the present study. The biggest limitation was the low number of patients with OBI, but the most of studies with OBI and cytokines analyses from 12 to 30 samples [59, 62, 80]; the second limitation was that there are few studies on the cytokine production profile in patients with OBI and finally, unfortunately, we could not include monoinfected HCV patients in our analyzes. However, our study was strongly compared to published data and can contribute to a better understanding of the complex response process related to cytokine production in OBI patients coinfected with HCV.