61
modulating activities include activation of macrophages, monocytes, dendritic cells,
natural killer (NK) cells, lymphocyte- activated killer cells, tumor-infiltrating lymphocytes, and other lymphocytes. Another important activity of these polysaccharides which have been documented is the prompt release of various cytokines
including interleukins, interferons, tumor necrosis factor and colony-stimulating
factors. Such polysaccharides are thus considered multicytokine inducers and this is
probably because of initiation of gene expression of diverse immunomodulatory
cytokines and cytokine receptors (Novak and Vetvicka 2008).
β-glucans have been documented to be potent immunomodulators with effects
on both innate and adaptive immunity (Tian et al. 2013). Dectin-1, which is a type
II trans- membrane protein receptor that binds β-1,3 and β-1,6 glucans, can initiate
and modulate the innate immune response (Schorey and Lawrence 2008). Dectin-1
is expressed on cells responsible for the innate immune response and has been found
in macrophages, neutrophils, and dendritic cells (Schorey and Lawrence 2008).
Dectin-1 accepts β-glucans found in the bacterial and fungal cell wall. Since
β-glucans are absent in human cells Dextrin-1 can conveniently trigger effective
immune responses including phagocytosis and proinflammatory factor production
which leads to the elimination of infectious agents (Schorey and Lawrence 2008).
The immunomodulatory activities of polysaccharides are related to their structures. Differences in molecular weight, tertiary structure/conformation, and composition all affect bioactivities of polysaccharide. Generally, polysaccharides with
a configuration of β-1-3, 1-4, or 1-6 branch chains are necessary for activity while
complex branch-chained polysaccharides with anionic structures and higher
molecular weights have greater immunostimulating activities (Kim and Kim 2017).
These differences in bioactivity may be due to differences in receptor affinity or
receptor- ligand interaction on the cell surface (Li et al. 2016, 2017). The immunostimulatory activities of many polysaccharides have been documented in some
studies in healthy human adults. Studies in healthy animals also indicated many
immune stimulating effects of various glucan products (Ahmad et al. 2012; Kamhi
et al. 2013; Tian et al. 2013).
The major manner through which polysaccharides from plants activate macrophages is through their interaction with specific receptors on cells. These receptors
are known as pattern recognition receptors. The macrophages are involved in
immune regulating processes. Macrophages play a significant role in all phases of
host defense that are both innate and adaptive immune responses to infection (Zhao
et al. 2015a, b). Macrophages play an essential role in all kinds of complex microbicidal functions, including the surveillance, chemotaxis, phagocytosis, and eventual degradation of the target organisms (Niu et al. 2017). Carbohydrates can interact
with macrophages and regulate these cells through diverse mechanisms. The possible mechanism is that macrophages bind and thus interact with the polysaccharides through toll-like receptor 4 (TLR4), CD14, dectin-1 and mannose receptor,
among others (Hollmig et al. 2009). Once the receptors are activated, there will be
downstream signal and generation of pro-inflammatory factors.
4 Bioactive Carbohydrates, Biological Activities, and Sources
modulating activities include activation of macrophages, monocytes, dendritic cells,
natural killer (NK) cells, lymphocyte- activated killer cells, tumor-infiltrating lymphocytes, and other lymphocytes. Another important activity of these polysaccharides which have been documented is the prompt release of various cytokines
including interleukins, interferons, tumor necrosis factor and colony-stimulating
factors. Such polysaccharides are thus considered multicytokine inducers and this is
probably because of initiation of gene expression of diverse immunomodulatory
cytokines and cytokine receptors (Novak and Vetvicka 2008).
β-glucans have been documented to be potent immunomodulators with effects
on both innate and adaptive immunity (Tian et al. 2013). Dectin-1, which is a type
II trans- membrane protein receptor that binds β-1,3 and β-1,6 glucans, can initiate
and modulate the innate immune response (Schorey and Lawrence 2008). Dectin-1
is expressed on cells responsible for the innate immune response and has been found
in macrophages, neutrophils, and dendritic cells (Schorey and Lawrence 2008).
Dectin-1 accepts β-glucans found in the bacterial and fungal cell wall. Since
β-glucans are absent in human cells Dextrin-1 can conveniently trigger effective
immune responses including phagocytosis and proinflammatory factor production
which leads to the elimination of infectious agents (Schorey and Lawrence 2008).
The immunomodulatory activities of polysaccharides are related to their structures. Differences in molecular weight, tertiary structure/conformation, and composition all affect bioactivities of polysaccharide. Generally, polysaccharides with
a configuration of β-1-3, 1-4, or 1-6 branch chains are necessary for activity while
complex branch-chained polysaccharides with anionic structures and higher
molecular weights have greater immunostimulating activities (Kim and Kim 2017).
These differences in bioactivity may be due to differences in receptor affinity or
receptor- ligand interaction on the cell surface (Li et al. 2016, 2017). The immunostimulatory activities of many polysaccharides have been documented in some
studies in healthy human adults. Studies in healthy animals also indicated many
immune stimulating effects of various glucan products (Ahmad et al. 2012; Kamhi
et al. 2013; Tian et al. 2013).
The major manner through which polysaccharides from plants activate macrophages is through their interaction with specific receptors on cells. These receptors
are known as pattern recognition receptors. The macrophages are involved in
immune regulating processes. Macrophages play a significant role in all phases of
host defense that are both innate and adaptive immune responses to infection (Zhao
et al. 2015a, b). Macrophages play an essential role in all kinds of complex microbicidal functions, including the surveillance, chemotaxis, phagocytosis, and eventual degradation of the target organisms (Niu et al. 2017). Carbohydrates can interact
with macrophages and regulate these cells through diverse mechanisms. The possible mechanism is that macrophages bind and thus interact with the polysaccharides through toll-like receptor 4 (TLR4), CD14, dectin-1 and mannose receptor,
among others (Hollmig et al. 2009). Once the receptors are activated, there will be
downstream signal and generation of pro-inflammatory factors.
4 Bioactive Carbohydrates, Biological Activities, and Sources