Augmentation of Cytolytic Activity in Murine Natural Killer Cells and Inhibition of Tumor Growth by the Ethanol Fraction of Oyster Extract

Immunomodulatory activity of aqueous extract from Crassostrea sikamea in the splenocytes of Sprague-Dawley rats

Crassostrea sikamea (C. sikamea) is used as an important edible and medicinal seafood in China. In the present study, an aqueous extract of C. sikamea (AECs) was prepared, and its immunomodulatory effects on rat splenocytes were studied. 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay revealed that AECs was able to promote splenocyte proliferation. Moreover, flow cytometry revealed that AECs treatment markedly altered the populations of splenic lymphocyte subtypes. Data from real-time quantitative PCR (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA) showed that AECs promoted the mRNA expression and secretion of TNF-α, IL-2, IL-6, IL-12, and IFN-γ. Mechanistically, p38 MAPK phosphorylation in splenocytes was significantly upregulated under AECs treatment and p38 MAPK inhibitor reversed the promoting effect of AECs on the expression of inflammatory cytokines. Collectively, our novel evidence suggests that AECs exhibits immunomodulatory activity in vitro, supporting the further application of C. sikamea as a potential functional food.

Effect of Natural Compounds on NK Cell Activation

Natural killer (NK) cells are lymphocytes of the innate immune system that survey the body for stressed and abnormal cells. The integration of signals that they receive through various inhibitory and activating cell surface receptors controls their activation and ability to kill target cells and produce cytokines. In this manner, phenotypically and functionally distinct subsets of NK cells help protect against microbial infections and cancer and shape the adaptive immune response. NK cells can use two different mechanisms to kill their targets, either by cytotoxic granule exocytosis or by induction of death receptor-mediated apoptosis. Death ligands belong to the tumor necrosis factor (TNF) family of ligands. Upon release in close proximity to a cell slated for killing, perforin forms pores in the cell membrane of the target cell through which granzymes and associated molecules can enter and induce apoptosis. NK cells are also involved in antibody-dependent cellular toxicity via the CD16 receptor. In addition to target recognition, NK cells can be also activated by treatment with multiple compounds with stimulatory properties. Apart from interleukins, which belong to the best characterized group of NK cell-stimulating compounds, vitamins and constituents extracted from plants also display the ability to activate NK cells. The current review characterizes several groups of NK cell-activating compounds: vitamins belonging to classes A, B, C, D, and E, polysaccharides, lectins, and a number of phytochemicals used in cancer research, exhibiting stimulatory properties when applied to NK cells. Although in most cases the exact mechanism of action is not known, constituents described in this review seem to be promising candidates for NK cell-stimulating drugs.

Restoration of stemness-high tumor cell-mediated suppression of murine dendritic cell activity and inhibition of tumor growth by low molecular weight oyster polysaccharide

Dendritic cells (DCs) play key regulatory roles in tumor immunity: increased activity of DCs infiltrating tumor tissues leads to enhancement of tumor immunity. Functions of DCs are also modulated by tumor cell-derived factors. Here, we investigated the effects of low molecular weight oyster polysaccharide (LMW-OPS) on differentiation and function of bone marrow-derived DCs (BMDCs) exposed to a conditioned medium (CM) obtained from spheres of stemness-high colorectal cancer cell lines CMT93 and CT26. The CM containing a detectable level of TGF-β1 was found to down-regulate the surface expression of major histocompatibility complex class II of BMDCs and to inhibit the potency of BMDCs to stimulate T cells. Those suppressions were partly restored and completely restored by addition of anti-TGF-β1 and LMW-OPS, respectively. Production of IFN-γ during allogeneic T cell responses was inhibited by the CM, whereas production of TGF-β1 was augmented by the CM. The IFN-γ profile was also reversed by addition of LMW-OPS. Nuclear translocation of β-catenin, but not that of NF-κB p65, was induced by TGF-β1. NF-κB p65 nuclear translocation, but not β-catenin nuclear translocation, was induced by LMW-OPS. Intraperitoneal injection of LMW-OPS significantly suppressed tumor growth in syngeneic tumor models using CMT93 and CT26 sphere cells, whereas it had no inhibitory effect on the proliferation of either cell line. The results demonstrated that LMW-OPS relieved stemness-high tumor cell-mediated suppression of BMDC function and indicated the in vivo anti-tumor activity of LMW-OPS in which re-stimulation of the activity of DCs infiltrating tumor tissues is presumed to be involved.