Research progress of functional food to enhance body immunity

Functional food is a kind of food with special health function, that is, it is suitable for specific people to eat, has the ability to regulate the body function, and does not cause any acute, subacute or chronic harm to the human body, and is not for the purpose of treatment. Its scope includes: enhance the body's physical fitness, prevent disease, regulate the body rhythm, restore health and delay aging food, etc. As a major category of functional food, the research content of functional food to enhance immunity mainly focuses on 4 types of substances, namely active polysaccharide, functional oil, Vitamin and active protein. Therefore, this paper expounds the research progress of functional food to enhance immunity in recent years from these 4 types of substances, in order to provide reference for the development of functional food related to enhance immunity in the future.

Polysaccharides exist widely in plant and microorganism cell wall, have various physiological activities, have immune regulation effect, can significantly enhance the body immunity. The immune activity mechanism of polysaccharides can be divided into the following types: (1) enhance the activity of macrophages. TANG et al. found through cell and animal experiments that the water-soluble polysaccharides, dilute alkali-soluble polysaccharides and concentrated alkali-soluble polysaccharides extracted from purple sweet potato can activate macrophages, and the three kinds of polysaccharides can enhance the phagocytosis activity of normal macrophages, among which the water-soluble polysaccharide has the best effect. (2) Promote antibody production. LIU et al. used cetyltrimethylammonium bromide (CTAB) modified Polygonum cuspidate polysaccharide as an assistant OVA antigen during mouse culture, and found that it could not only promote the production of OVA specific antibody IgG in serum, but also activate dendritic cells, promote lymphocyte proliferation, and significantly improve the humoral immunity level of mice. (3) Activate signaling pathways and promote the expression of immune-related genes. HAN et al. found that polysaccharides extracted from young barley leaves can effectively improve cyclophosphamide induced body weight loss, spleen cell proliferation and natural killer (NK) cytotoxic activity in mice by enhancing the tyrosine kinase (JAK) -signal transductor and transcriptional activator (STAT) 1 signaling pathway. The mRNA expression of helper T cell 1(Th1) and helper T cell 2(Th2) cytokines, immune gene T-BET and T cell specific transcription factor GATA3 were significantly increased. (4) Promote lymphocyte transformation and proliferation. LU et al. extracted, purified and selectively modified Lilium selenide polysaccharides (LP), and obtained 9 kinds of Lilium selenide polysaccharides (SLP1 ~ SLP9), and conducted immune studies on them. In vitro results showed that SLP6 showed the strongest activity in promoting single and synergistic lymphocyte proliferation. In vivo experiment results showed that SLP6 can promote lymphocyte proliferation.

The oils with special physiological functions are usually called functional oils. Some special nutrients or active substances contained in them can directly or indirectly improve the immune function of the body and play a role in the prevention and treatment of some diseases. The active substances in functional fats are mainly polyunsaturated fatty acids, followed by phospholipids. In recent years, many researches have been made on functional oils and fats. For example, the addition of linseed oil and sesame oil in the feed can accelerate the metabolism of eicosane in carp, and induce lipopolysaccharide (LPS) to produce better immune regulatory response more effectively. Liu Ruocui et al. took cod liver oil as the research object, orally gavage mice for one month, and then measured humoral immunity, cellular immunity, NK cell activity and mononuclear macrophage function of the mice. The results showed that cod liver oil significantly enhanced the immune function of mice. The effects of the mixture of lycium barbarum seed oil and linseed oil on immune organ viscera/body ratio, phagocytosis function of mononuclear macrophages, cellular immunity, humoral immunity and NK cell activity in mice were tested by Jie Yujie et al. The results showed that the mixture of lycium barbarum seed oil and linseed oil had the function of enhancing immunity in mice.

03 vitamin to enhance immunity food

Vitamin is a kind of special nutrients in the body. Although its amount is small, it is necessary for the body and cannot be produced by the body itself, so it needs to be consumed from the diet. Unlike sugars, proteins and fats, vitamins do not produce energy or cells, but play an important role in regulating metabolism. Long-term deficiency of vitamins can lead to a decline in immunity. The current research on vitamin immunity mainly focuses on vitamin C and vitamin D 2. Vitamin C is maintained at high levels in most immune cells and can influence many aspects of the immune response. QIN et al. evaluated the effect of vitamin C supplementation on the immune response against Plasmodium infection in BALB/C mice, and found that oral administration of 25 and 250 mg/(kg·d) vitamin C could significantly reduce the level of parasitemia in the early stage of infection, and the number of activated Th1 cells and macrophages in the vitamin C supplementation group were higher than those in the group without vitamin C supplementation. Vitamin D is a steroid derivative. In recent years, many studies have found that vitamin D has a unique role in intestinal immunity. For example, vitamin D plays an important role in the pathogenesis of inflammatory bowel disease (IBD) by influencing the gut microbiome and inflammatory response. Vitamin D deficiency was reported in 38.1 percent of patients with Crohn's disease (CD) and 31.6 percent of patients with ulcerative colitis (UC). The effect of vitamin D on intestinal microflora is in favor of probiotics rather than pathogenic microorganisms, so it is believed that vitamin D can enhance the body's immune function by maintaining the stability of intestinal microflora.

In addition to the immune activity of the two main vitamins, the researchers found that other vitamins also have some immune strengthening function. For example, PENKERT et al. found in their studies that retinoic acid, the oxidative metabolite of vitamin A, could affect cytokine transcription and protein expression in macrophages and epithelial cells. In addition, it was found that dendritic cells, induced T cells, B cells migration and settlement, and presenting cells to pathogens were all affected by vitamin A. QIANG et al. fed tilapia with different doses of vitamin E for 55 days to observe its growth performance and non-specific immunity. The results showed that vitamin E deficiency significantly decreased the activities of superoxide dismutase, glutathione peroxidase and catalase, increased the content of malondialdehyde and caused oxidative damage. With the increase of vitamin E level, the non-specific immune response can be enhanced and the expression level of some immune-related genes can be increased.

Protein is a kind of essential nutrients needed by human body, and is also the basic substance of the body's immune defense function. It is closely related to the occurrence of immune tissue and the development of immune organs. Therefore, many scientists focus their research on the immunomodulatory function of proteins and their breakdown products. Chen Yao et al. orally administered 0.83, 1.67, 5.0 g/kg·BW protein powder to mice for 30 days, and the results showed that the protein powder could significantly improve the serum hemolysin level, lymphocyte transformation ability and the number of antibo-producing cells of mice. Qin Lanxia carried out functional evaluation on a commercially available bovine colostrum powder product with 10% IgG content, which showed that the bovine colostrum powder could enhance the phagocytosis function of mononuclear macrophage, the activity of NK cells, cellular immunity and humoral immunity.

Active peptide is composed of several to dozens of amino acids with different structure order. It is a multifunctional compound after protein enzyme. WANG et al. found that lienal peptide (LP) extracted from the spleen of healthy calves can significantly regulate immune system function. LP can enhance immune function in immunosuppressed mice induced by cyclophosphamide. After LP treatment, the activation rates of bone marrow B lymphocytes, spleen lymphocytes, NK cells and peritoneal macrophages were significantly increased. Ma Ziqi et al. demonstrated that the immunoactive peptide of corn yellow powder could promote the proliferation of spleen lymphocytes in mice in a dose-dependent manner.

Amino acids are metabolites of protein, and some amino acid catabolic pathways have become key checkpoints of immunity during immune regulation. Amino acids may act as signaling molecules to regulate metabolic pathways in inflammatory immune processes. PEREIRA et al. found that feeding Nile tilapia with Gln and Arg could improve its innate immune function. It has also been reported that the addition of Trp in vitro can promote the rapid proliferation of intestinal lactobacillus and affect intestinal immune balance in mice. However, the regulatory effects of Trp on the host intestinal immune system and intestinal flora composition are not caused by Trp itself, but are closely related to the endogenous metabolites of Trp and Trp microbial metabolites.

At present, the development of functional food to enhance immunity has become a new way for people to pursue health. More and more research focuses on the development of functional food to enhance immunity. Although some areas of research have made good progress in developing a range of functional immune-boosting products, there are still some problems in general. For example, it mainly focuses on the development of functional foods that enhance non-specific immunity, while there are few researches on functional foods that enhance specific immunity. The basic research is not enough, and the functional factors to enhance immunity are few; Product development mainly focuses on the first and second generation functional food, while the third type of products with advanced technology and high-tech production are few. If these problems can be solved in the future, it will greatly promote the development of functional foods that enhance immunity.

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2023-6-1

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