This present study shows that 8-week supplementation of Chlorella tablets may give a beneficial immunostimulatory effect to normal (uninfected) people by enhancing the NK cell activity and producing INF-γ and IL-12 as well as IL-1β, the Th-1 cell-induced cytokines.
Helper T lymphocytes (Th) are divided into two functional subclasses, Th-1 and Th-2 cells based upon the cytokines that they produce and their effects on cell mediated and humoral immunity . Th-1 cells produce IL-2, INF-γ, TNF-α and IL-12 and enhance cell-mediated immunity, thereby inhibiting cell-mediated immunologic activities. On the other hand, Th-2 cells produce IL-4, IL-5, IL-6 and IL-10, and upregulate humoral immunity. Th-1 and Th-2 derived cytokines also cross-regulate each other in various clinical conditions. Hasegawa et al reported in his mice model infected with Listeria monocytogenes that Chlorella extract (from Chlorella vulgaris, CVE) augmented IL-12 and IFN-γ , both of which promote the differentiation of naive CD4+ T cells into Th-1 cells producing IFN-γ, but inhibited the generation of Th-2 cells producing IL-4. In his other report, oral administration of CVE in mouse model inhibited immunoglobulin E (IgE) production against casein together with an impaired Th-2 response . Ewartet al shows that Chlorella extract (from Chlorella pyrenoidosa, CPE) induces a Th-1 patterned cytokine response (IFN- γ and TNF-α) and a strong anti-inflammatory regulatory cytokines response (IL-10) in human PBMC stimulated ex vivo. In our study, subjects who consumed Chlorella tablets for 8 weeks had a significant increase in serum levels of INF-γ and an increasing tendency in the levels of IL-12 compared with those who consumed placebo, which indicates that Chlorella supplementation may induce the production of INF- γ and IL-12 favoring a Th-1 mediated immune reaction in humans.
We also found the increased levels of serum IL-1β which is a member of the IL-1 cytokine family and produced by activated macrophages . This cytokine is an important mediator of the inflammatory response, and is involved in a variety of cellular activities, including cell proliferation, differentiation, and apoptosis . IL-1β stimulates multiple cells to act as immune or inflammatory response effector cells. Hunter et al reported in his severe combined immuno-deficient mice models that IL-1β is required for IL-12 to stimulate production of IFN-γ by NK cells . According to Tominaga et al, IL-12 and IL-1β synergistically induce T cells to proliferate and produce the IFN-γ and IL-12-stimulated T cells which responded to IL-18 or IL-1β by their proliferation and IFN- γ production, although the levels of IL-1β-induced responses were lower. Our result may be partially in accordance with the report of Ishikawa et al showing that a polysaccharide-rich fraction from Chlorella pyrenoidosa induced IL-1β and TNF-α in macrophage cells . Taken together, Chlorella cells appear to contain immunostimulatory principles that stimulate a Th-1 based response. However, we did not measure the Th-2 derived cytokines such as IL-4 or IL-6, thus we may need to confirm these cytokines in further studies.
In our study, people who consumed Chlorella had a significant increase in Natural Killer (NK) cell activities. This result might be partly in accordance with the report of Dantas et al showing that oral administration of Chlorella extract (CVE) significantly increased the NK cell activity in normal (non-infected) mice as well as in the Listeria monqtogenes infected mice . In addition, the CV-treated animals presented a dose-related increased survival rate. NK cells were first identified by their cytotoxtc activity against tumor cells, suggesting a role in immunological surveillance against neoplasia. Emerging evidences demonstrated that NK cells are important mediators of innate resistance against a variety of pathogenic intracellular microorganisms . Their main function is the production of early IFN-γ, which is crucial to activate antimicrobial macrophage functions [37–42]. The kinetics of IFN-γ production by NK cells following infection is extremely fast, providing a source of functional cytokine at the critical time of the T-cell expansion [39, 43, 44]. In our study, changed level of NK cell activity after the intervention shows a significant positive relationship with that of serum IFN-γ. Signficanty strong positive correlations were also observed among the changed levels of IFN-γ, IL-12 and IL-1β, Th-1 patterned cytokines.
We may need to consider further study with increased number of study subjects and for longer period in the future, to confirm and clarify the result pattern. As shown in the Figures, serum levels of INF- γ and IL-12 were significantly decreased in the placebo group after 8 weeks, even though the net change of these cyotkines were significantly bigger in the Chlorella group than in the placebo group. We tried to search the factors which might affect the decrease of these parameters in the placebo group, but it is not easy to address the reason in a word. First, we thought the possibility of lactose, the contents in the placebo affecting cytokine levels, but it seemed not influence the cytokine levels. Second, there were no significant difference in the baseline value between the two groups, and the net change values were generally much greater in the Chlorella group than those in the placebo group, even though the direction for increment or decrement were not the same between the two groups. However, the correlation pattern among NK cell activity and cytokines were consistently in the positive direction, which may indicate that the measurements and the results are reliable.