Immunomodulatory and immunostimulating effects of beta-glucan
Nutritional immunology is a new science. It will be more effective when the relationship between nutrition and the immune system is better understood. That’s what we’re going to focus on in this review.
Infectious diseases, possibly contagious in swine, avian, bovine, and other species, cause damage, corroborated by the reduction in the use of antibiotics, increasingly legislated. It increases the importance of the immune system.
Currently, there is an intense scientific movement devoted to immune tissue, its development, and functioning, seeking more effective technologies, with resistance to antigens, and ultimately, more production.
In recent decades, Immunosuppressive viruses such as Gumboro disease in birds and circovirus in swine have greatly catapulted the development of veterinary immunology. This coincided with the advent of molecular biology and technological support, high-tech vaccines, and new diagnostic methods.
The identification of dendritic cells, for example, occurred at this time, as well as some specifications of the B cell and some immunoglobulins.
Together with recombinant vaccines, the development of more efficient and safer adjuvants is another example.
The enhancement of the immune response, intestinal or general, and reducing dependence on antibiotics is great. Today there is a multitude of molecules promoted for this and other purposes. Further on, categories of compounds in use are listed.
There are experimental studies to assess their effectiveness; some prove benefits, while others do not, reflecting the lack of adoption of an adequate experimental methodology.
These are the most commonly used categories of compounds:
Strictly speaking, benefits are sought or promoted, such as:
Competition, adsorption, and exclusion of pathogens;Decreased PH and increased anaerobic activity;Production of SCFA (short-chain fatty acids);
Reduction of pathogen adherence to enterocyte receptors;
Reduction of intestinal permeability;
Increase of intestinal immunity and regulation of inflammation;
Greater resistance to intestinal aggressors.
BETA-GLUCAN Beta-glucan, notably in humans, has been studied in some pathologies such as diabetes. This compels experimentation with production and companion animals to control various pathologies, although with a more discrete representation.
Let’s stick to dietary fiber. According to Rosch, C, dietary fiber is a carbohydrate polymer with three or more monomer units that do not undergo digestion.
They are D-glucose monomer polysaccharides joined by B-glycosidic bonds, with various conformations and part of the fungi cell wall, for example. The same reference characterizes beta-glucan also as hemicellulose.In a recent review in 2016, beta-glucan does not fall into the category of fermentable prebiotic by lactobacillus, as are FOS, GOS, and MOS, but rather as an immunomodulator of the response.
For information regarding the fermentative characteristics, in vitro and in vivo of fibers in general, refer to the relevant bibliography.
Strictly speaking, beta-glucan obtained by alcoholic fermentation is considered quite effective in this function, so there is a direct relationship with the industrial method of obtaining it.
THE IMMUNE SYSTEM
To better understand how beta-glucans work, let’s briefly review the immune system. Above are the cells involvedin immune and inflammatory reactions, considering innate and adaptive immunities.The first is nonspecific, recognizes and eliminates the pathogenic agent quickly, and constitutes the main focus of the immediate defense.The adaptive is slow and specific, occurs through the production of immunoglobulins and memory cells, and promotes the pathogenic agents’ elimination.
Thus, resistance to an agent defines immunity. But what gives the immune system the ability and adaptability to mobilize a network of specialized cells and proteins to defend against infectious agents and altered cells?This is what we propose to discuss now.
Lymphoid tissues and their resident cells
Thymus – T and B cells, macrophages and antigen-presenting cells (DCs or dendritic Cells);
Spleen – white pulp (T and B lymphocytes), the red pulp (erythrocytes);
Bone marrow – all lineages, including monocytes, macrophages, except T cells;
Lymph nodes – B and T cells, with B in the cortex and T in the medulla of the organ and macrophages. In pigs, B cells settle in the cortex and T cells in the medulla. It is the opposite of what happens in other animals and man;
Jejunal Peyer’s patches – B cells, macrophages, and DCs;
Ileal Peyer’s patches – B cells;
Tonsils – T and B cells, macrophages, and DCs;
Fabricius bursa – mainly B cells.
Intestine
The intestine is the organ that most includes defense cells. Immune cells
(T and B lymphocytes) located in the mucosa differentiate and develop as they are stimulated by pathogens or foreign molecules.
T cells depend on macrophages in this intermediation. B cells do not because they have globulin receptors.
Note (figure 2) that there are differences in the populations of immune cells in the different intestinal germinal centers.
They occur in a more significant expansion in the lateral panels, with a profusion of B cells, notably.
In the central panel, this activity is more discreet.
Figure 2: Immune cells in the mucosa. Osman (2011)
SPF animals have a lower distribution of immune cells, which increases with age and exposure. There are about 250 PP (Peyer’s patches) and numerous follicles at the level of the gastrointestinal mucosa so that no change in diet and biome goes unnoticed by the immune system of vertebrates, including fish.
In the germ nuclei formed in the immune reaction, there are regions of B cells and T cells, between macrophage cells and others. In the ganglia, the same process occurs.
Together with recombinant vaccines, the development of more efficient and safer adjuvants is another example.
