## 8 The Immune Response and Its Interaction with the Gut Microbiota  
The immune response is a fundamental determinant of an individual's susceptibility to infections, as well as the duration and resolution of such infections. The immune system is broadly classified into two primary components: the innate immune system and the adaptive immune system [64]. The innate immune system provides a nonspecific yet immediate line of defense through various protective mechanisms. These mechanisms include physical barriers, such as the skin and mucosal membranes, which serve as the first layer of defense against pathogenic invasion. Additionally, chemical barriers, such as antimicrobial proteins and enzymes, further contribute to host protection. Moreover, innate  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt}} \hline \hline
**Aspect** & **Details** \\ \hline Innate Immune Response in HCV & Cellular innate immune response is crucial in host defense against HCV infection \\ \hline Role of NK Cells & NK cells are essential for early antiviral immunity, comprising 30–50\% of liver lymphocytes \\ \hline NK Cell Classification & CD16 + CD56 dim NK cells: cytotoxic, strong effector functions (target cell lysis) \\  & CD16 – CD56 bright NK cells: immunoregulatory, cytokine-producing \\ \hline Impact of Other Infections on NK Cells & Infections like cytomegalovirus, Epstein-Barr, herpes virus reduce NK cell cytotoxic activity \\ \hline NK Cell Functions in HCV Infection & Secrete pro-inflammatory cytokines (TNF-\(\alpha\), IFN-\(\gamma\)) to suppress HCV replication. \\ \hline NK-Cell-Induced Liver Injury & Cytotoxic response can lead to unintended liver injury and inflammation \\ \hline Killer Immunoglobulin-like Receptors (KIRs) & KIRs interact with MHC class I molecules, regulating NK cell activity \\ \hline NK Cells in Early HCV Infection & Contribute to early viral load reduction through cytolysis, cytokine secretion, and activation of other immune cells \\ \hline Adaptive Immune Response Activation & Dendritic cells (APCs) process and present viral antigens to activate CD4+ helper T cells, CD8+ cytotoxic T cells, and B cells \\ \hline Interaction between Dendritic Cells and NK Cells & NKp30 receptor triggers IL-12 and IL-15 release from dendritic cells, enhancing NK cell function and cytokine production (IFN-\(\gamma\), TNF-\(\alpha\)) \\ \hline Natural Killer T (NKT) Cells & NKT cells comprise 26\% of intrahepatic lymphocytes, secreting IFN-\(\gamma\), TNF-\(\alpha\), IL-2 \\ \hline NKT Cells in Chronic HCV & Conflicting findings on NKT cell frequency: some studies show increased, others show decreased NKT cells in the liver of chronic HCV patients \\ \hline NKT Cells Cytokine Production in HCV & Altered cytokine profiles, particularly IL-13, which regulates cell-mediated immunity and may influence chronic HCV progression \\ \hline \hline \end{tabular}
\end{table}
Table 2: HCV and immune system—key aspects.  
immune cells--including granulocytes, macrophages, and natural killer (NK) cells--play a crucial role in pathogen recognition and elimination [65].  
In contrast, the adaptive immune system is highly specific and is primarily mediated by T and B lymphocytes. T cells are responsible for identifying and responding to pathogens that have invaded host cells, thereby constituting the cellular arm of adaptive immunity. Moreover, T cells exert regulatory control over B cells, which are responsible for antibody production. These antibodies bind to specific antigens and facilitate pathogen neutralization, a process that occurs within the bodily fluids, thus forming the basis of humoral immunity [66].