65
polysaccharides may have no direct ability to inhibit tumor cells, they may provide
antitumor effect by enhancing the immune function of the body. The immunomodulatory effect of polysaccharide is therefore considered as an important mechanism
for their antitumor effect (Carvalho et al. 2016). Polysaccharides also activate the
reticuloendothelial system (RES), remove aged cells, foreign bodies and pathogens.
Furthermore, they promote the formation of IL-1, IL-2, TNFα, INF-r, NO, etc.
which regulate antibodies in the body and complement their formation. All these
improve the body’s antitumor immunity (Carvalho et al. 2016). The indirect antitumor activities of polysaccharides can be done by:
(a) Activation of macrophages. Macrophages are important immune cells with
multiple functions, they can actively swallow and clear the granular foreign
antigens or directly kill pathogenic microorganisms, also can secrete a variety
of bioactive substances, which almost are involved in all immune responses of
the body. Polysaccharides can stimulate macrophages and enhance the phagocytosis of macrophage. They also promote the production and release of mononuclear factors, activate lymphocytes, in order to activate the immune response
of tumor cells (Levine and Puzio-Kuter 2010).
(b) Activation of Lymphocytes. T and B lymphocytes play critical roles in cellular
immunity as well as humoral immunity. B cells produce antibodies to mediate
humoral immunity, whereas T cells induce cell-mediated immunity. In effect, B
lymphocytes produce antibodies while T lymphocytes help kill tumor cells and
help to control immune responses. Lentinan which is a β-glucan polysaccharide
extracted from the fruit body of shiitake (Lentinus edodes) is a typical T cell
activator (Yu et al. 2009; Zhang et al. 2011).
(c) Activation of NK cells. NK cells are naturally occurring non-specific immune
killer cells. They move freely in the blood to lyse cancer cells and other cells
virus-infected cells (Tian et al. 2013).
(d) Promotion of antibody formation and complement activation. Complement is a
series of proteins with prokaryotic activity in the blood that can fight against
pathogenic microbes through synergistic actions with antibodies or phagocytic
cells (Meri 2016).
(e) Promoting the secretion of cytokines. Cytokine (CK) plays a vital role in the
mechanism of antitumor effect. NO, IL-2, TNF-α, TNF-β, INF-γ, and other
cytokines can activate the immune response of tumor cells thereby reflecting
the antitumor activity (He et al. 2017). Interleukin-2 (IL-2) is synthesized by T
cells, particularly, CD4
+
T cells when stimulated by antigen or mitogen. Other
cells such as mononuclear macrophages, B cells, NK cells, etc. can also produce IL-2. IL-2 is a naturally occurring cytokine with immune-modulating and
antineoplastic effects. It regulates lymphocyte activation, activates macrophages, and participates in specific immunity and non-specific immunity
(Pandya et al. 2018; Tian et al. 2013).
(f) Promoting the synthesis of dendritic cells. Dendritic cells (DCs) are antigenpresenting cells, and also immune -regulatory cells. DC can initiate an initial
lymphocyte-mediated immune response. Polysaccharides can trigger innate
4 Bioactive Carbohydrates, Biological Activities, and Sources
polysaccharides may have no direct ability to inhibit tumor cells, they may provide
antitumor effect by enhancing the immune function of the body. The immunomodulatory effect of polysaccharide is therefore considered as an important mechanism
for their antitumor effect (Carvalho et al. 2016). Polysaccharides also activate the
reticuloendothelial system (RES), remove aged cells, foreign bodies and pathogens.
Furthermore, they promote the formation of IL-1, IL-2, TNFα, INF-r, NO, etc.
which regulate antibodies in the body and complement their formation. All these
improve the body’s antitumor immunity (Carvalho et al. 2016). The indirect antitumor activities of polysaccharides can be done by:
(a) Activation of macrophages. Macrophages are important immune cells with
multiple functions, they can actively swallow and clear the granular foreign
antigens or directly kill pathogenic microorganisms, also can secrete a variety
of bioactive substances, which almost are involved in all immune responses of
the body. Polysaccharides can stimulate macrophages and enhance the phagocytosis of macrophage. They also promote the production and release of mononuclear factors, activate lymphocytes, in order to activate the immune response
of tumor cells (Levine and Puzio-Kuter 2010).
(b) Activation of Lymphocytes. T and B lymphocytes play critical roles in cellular
immunity as well as humoral immunity. B cells produce antibodies to mediate
humoral immunity, whereas T cells induce cell-mediated immunity. In effect, B
lymphocytes produce antibodies while T lymphocytes help kill tumor cells and
help to control immune responses. Lentinan which is a β-glucan polysaccharide
extracted from the fruit body of shiitake (Lentinus edodes) is a typical T cell
activator (Yu et al. 2009; Zhang et al. 2011).
(c) Activation of NK cells. NK cells are naturally occurring non-specific immune
killer cells. They move freely in the blood to lyse cancer cells and other cells
virus-infected cells (Tian et al. 2013).
(d) Promotion of antibody formation and complement activation. Complement is a
series of proteins with prokaryotic activity in the blood that can fight against
pathogenic microbes through synergistic actions with antibodies or phagocytic
cells (Meri 2016).
(e) Promoting the secretion of cytokines. Cytokine (CK) plays a vital role in the
mechanism of antitumor effect. NO, IL-2, TNF-α, TNF-β, INF-γ, and other
cytokines can activate the immune response of tumor cells thereby reflecting
the antitumor activity (He et al. 2017). Interleukin-2 (IL-2) is synthesized by T
cells, particularly, CD4
+
T cells when stimulated by antigen or mitogen. Other
cells such as mononuclear macrophages, B cells, NK cells, etc. can also produce IL-2. IL-2 is a naturally occurring cytokine with immune-modulating and
antineoplastic effects. It regulates lymphocyte activation, activates macrophages, and participates in specific immunity and non-specific immunity
(Pandya et al. 2018; Tian et al. 2013).
(f) Promoting the synthesis of dendritic cells. Dendritic cells (DCs) are antigenpresenting cells, and also immune -regulatory cells. DC can initiate an initial
lymphocyte-mediated immune response. Polysaccharides can trigger innate
4 Bioactive Carbohydrates, Biological Activities, and Sources