## 3 Bioactivity of _Chlorella vulgaris_ Compounds
### Immunomodulatory Activity  
_C. vulgaris_ is known for its ability to enhance both innate and adaptive immune responses, largely through the activation of cytokine production. Its polysaccharides stimulate the release of key cytokines like interferon-gamma (IFN-\(\gamma\)) and interleukin-2 (IL-2), which are essential for activating immune cells such as natural killer cells and T cells [20]. IFN-\(\gamma\) enhances macrophage and natural killer (NK) cell activity, while IL-2 promotes T cell activation and proliferation, boosting the body's defense against infections and cancer cells [65; 67]. This immunomodulatory effect of _Chlorella_ has been observed in both animal studies and human clinical trials, making it a promising natural supplement for supporting overall immune function [73]. For instance, Ramirez-Coronel et al. [75] found that _C. vulgaris_ supplementation improved immune responses in common carp, indicating its potential benefits in aquaculture. This aligns with findings from Velankanni et al. [7], who noted that _Chlorella_ can modulate gut microbiota and enhance immune responses, suggesting its utility in managing autoimmune conditions. Such immunomodulatory effects, combined with its antioxidant capabilities, make _C. vulgaris_ a promising candidate for dietary therapies aimed at reducing oxidative stress and enhancing overall health. _C. vulgaris_ also improves the function of macrophages, NK cells, and cytotoxic T cells, enhancing immune surveillance against pathogens and cancer cells [73]. Additionally, it helps regulate the balance between pro-inflammatory and anti-inflammatory cytokines, increasing anti-inflammatory cytokines like IL-10, which helps control inflammation and prevent tissue damage [65; 67]. By modulating the NF-\(\kappa\)B pathway and boosting IL-10 production, _C. vulgaris_ effectively serves as both an anti-inflammatory agent and an immunomododulator.  
In vitro trials and animal studies have shown that _Chlorella_ and its extracts play a significant role in modulating immune responses to tumors, as well as bacterial and viral infections [76; 77; 78; 79; 80; 81; 82; 83]. Research indicates that these organisms can enhance the activity of immune cells, boost cytokine production, and improve overall immune function, suggesting their potential as natural immunotherapeutic agents. As for human trials, Kwak et al. [65] demonstrated that an 8-week intervention with _C. vulgaris_ resulted in significant increases in serum concentrations of interferon-\(\gamma\) (\(p<0.05\)) and interleukin-1\(\beta\) (\(p<0.001\)), along with a tendency for interleukin-12 levels to rise (\(p<0.1\)) compared to the placebo group. Additionally, NK cell activity was notably enhanced in the _Chlorella_ group, correlating positively with the serum levels of interleukin-1\(\beta\) (r = 0.280, \(p=0.047\)) and interferon-\(\gamma\) (r = 0.271, \(p<0.005\)). These findings suggest that short-term _Chlorella_ supplementation may provide beneficial immunostimulatory effects by enhancing NK cell activity and promoting the production of Th-1 cell-induced cytokines, including interferon-\(\gamma\), interleukin-12, and interleukin-1\(\beta\), in healthy individuals.