Food is a source of life support and plays an important role in body functions. Therefore, functional foods with immunomodulatory functions are highly valued. To protect against infections, the immune system is able to recognize foreign components and maintain the body’s normalcy by eliminating non-self components. The representative organ of the body with large amount of exposure to antigenic substances is the digestive tract, which is stimulated by the presence of a large number of intestinal bacteria on the surface of the intestinal mucosa. In other words, the immune system of the intestinal mucosa is the largest immune-associated tissue in the body, and it plays an important role in defending the body from diseases.
The mucosal surface has the function of physical and chemical isolation from various stimuli such as food components, pathogenic microorganisms, intestinal bacteria and digestive enzymes. The gastrointestinal lymphoid tissue (GALT) accounts for about 70% of the body’s immune system, and the submucosa of the intestines can be divided into three layers: the epithelial layer, the basement membrane, and the lamina propria of the mucosa. The epithelial layer is composed of epithelial cells and intraepithelial lymphocytes, while the lamina propria contains blood vessels, lymphatic vessels, and nerves. In addition to epithelial cells, the intestinal surface also contains a type of non-villous dome-shaped cells, called M-cells, which allow the passage of microorganisms or antigens. Underneath the M-cells are Peyer’s patches (PP), and the antigen presenting cells (APC) in these lymphoid aggregates provide immune cells for immune recognition. The immune cells present in the lamina propria of the mucous membrane also contain B-cells, helper T-cells, killer T-cells, monocytes, macrophages, dendritic cells, granulocytes, and mast cells, etc., and the antibody is the most abundant in the form of IgA, which is the most prominent form of the antibody. Secretory IgA in the intestinal tract plays a role in defense against foreign pathogens by binding to them directly, thus preventing them from adhering to the surface of epithelial cells, making IgA as an important immune defense in mucosal immunity.
In the state of oral immune tolerance, the ingestion of food antigens orally results in systemic acquisition of these antigens, representing a distinctive characteristic between oral immune tolerance and the intestinal immune system. Failure in this response can lead to certain immune reactions commonly associated with food allergies. Experiments correlating oral immune tolerance with gut bacterial stimulation were conducted using induced experiments on germ-free mice and conventionally raised mice (control group). These experimental mice were orally exposed to specific protein antigens for a defined period while simultaneously receiving identical protein antigens injected intraperitoneally. The antibody levels in the blood were measured to assess the response. Results indicated a significant increase in IgG1 and IgE antibodies in germ-free mice, whereas the control group showed no significant elevation in antigen-specific IgG1, IgG2a, and IgE antibody levels. This suggests the inhibition of CD4+T cells within the intestinal immune system. Hence, it can be inferred that stimulation from intestinal bacteria plays a pivotal role in regulating the intestinal immune system. Probiotics generally refer to microorganisms that can improve the balance of microbial flora within the host and are beneficial to the host through one or multiple microorganisms. Observations by Russian scientists regarding the dietary habits of Bulgarians revealed that regular consumption of fermented milk contributed to an extended lifespan. Lactic acid bacteria found in fermented milk were observed to inhibit the growth of harmful bacteria, thereby delaying the aging process. Studies have also indicated that feeding mice fermented milk increased the secretion of IgA in their intestines, demonstrating enhanced resistance in the intestinal mucosa. Additionally, administering fermented milk to pregnant women suffering from allergic dermatitis reduced the incidence of allergic dermatitis in infants after birth. As of today, numerous ongoing studies continue to explore the wide-ranging applications and diverse functionalities of probiotics. Beyond maintaining microbial balance within the body, the continued pursuit of probiotic intake aims to reduce harmful intestinal bacteria and improve overall health. Achieving this goal is imperative for enhancing bodily well-being.
Association of other dietary components with immune response
In lipid studies, research has shown that the addition of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) to human monocyte cells significantly inhibits the secretion of cell cytokines associated with inflammatory reactions. Furthermore, studies have also revealed that feeding DHA can lower serum IgE concentrations in mice and alleviate the onset of allergic symptoms. In the realm of vitamins, they are widely perceived as essential nutrients crucial for overall health. Currently, several reports have been proposed regarding their association with the immune system, including vitamin A, B6, C, D, E, carotenoids, lutein, and coenzyme Q10. Literature suggests that supplementing vitamin C can enhance natural killer cell activity, while supplementing vitamin A and carotenoids can increase cytokine secretion. Additionally, supplementation of vitamin E has shown the ability to reduce the production of IgG1 and IgE antibodies, thereby exhibiting a potential to mitigate allergic responses. Vitamin deficiencies not only lead to deficiency-related symptoms but also disrupt immune function, highlighting the paramount importance of understanding the role of vitamins in maintaining our health.
Minerals, like vitamins, significantly impact immune function when deficient. The group of minerals abundant in the human body includes calcium, magnesium, sodium, potassium, phosphorus, and chlorine, totaling six. A second group, termed trace elements due to their lower body concentrations, comprises eight minerals: iron, iodine, zinc, selenium, copper, manganese, chromium, and cobalt. Each mineral, akin to vitamins, serves specific bodily functions. For instance, minerals are pivotal constituents in skeletal structure and enzymatic processes, contribute to maintaining acid-base balance, and support normal neurological and muscular function. Certain trace minerals among these elements can even prevent or combat disease onset. Thus, ensuring an adequate intake of minerals is crucial.
In recent years, young women have been experiencing inadequate food intake due to excessive weight loss practices, while elderly individuals have faced reduced intake levels, leading to nutritional deficiencies. These factors contribute to insufficient mineral intake, consequently impacting immune function and lowering metabolic activity. To maintain health, it is essential to judiciously utilize food sources and incorporate these practices into daily dietary habits. To maintain gut immune health, individuals can adopt a series of methods. A balanced diet is particularly crucial, emphasizing the consumption of foods rich in fiber, probiotics, and various nutrients, aiding in the support of gut immunity. Additionally, avoiding exposure to adverse environmental conditions and managing stress through appropriate lifestyle practices also contribute to preserving gut immune health.
Reference: Seafood Technology Division, Fisheries Research Institute.