Study on Echinacea for Immune System

Echinacea purpurea (L.) Moench is a perennial herb in the Asteraceae family, also known as “purple coneflower”. Native to North America, it has been found to have eight species and several varieties. Researchers have currently developed Echinacea purpurea (L.) Moench (also known as purple coneflower), purpurea (L.) Moench (also known as purple coneflower), Echinacea angustifolia (DC.) Hell and Echinacea pallida (Nutt.) Nutt have been developed as medicines by researchers. Echinacea has various pharmacological effects, including immunomodulation, antiviral, anti-inflammatory, antibacterial and regeneration-promoting effects. It also has a certain effect on lung function and the cardiovascular system, and can be used as a biological enhancer after surgery. The history of Echinacea use can be traced back to the 18th century, when North American Indians first used it medicinally to treat trauma, sepsis and toothache. In most Western countries, it is used to prevent and treat upper respiratory tract diseases such as colds and influenza, as well as skin diseases and asthma [1].

Echinacea is valued by researchers as a broad-spectrum immunomodulator and immunostimulant. Echinacea contains a variety of active compounds that can work together or against each other in specific proportions. The main immunologically active ingredients include high molecular weight components such as polysaccharides and glycoproteins, derivatives of caffeic acid, and various alkylamides. These main immunologically active ingredients can stimulate the body's immune system, enhance T cell activity and the phagocytic ability of macrophages, thereby enhancing the body's resistance to viral and bacterial infections. In recent years, there have been many studies on the immunological activity of Echinacea, but there is a lack of a systematic summary of its immunologically active ingredients and mechanisms of action. This study aims to summarize the immunological components of Echinacea and the mechanisms of action that enhance immunity, to provide a reference for future research on the immunological effects of Echinacea.

1 Immunologically active ingredients

1.1 Polysaccharides and glycoproteins

Echinacea polysaccharides and glycoproteins are important active ingredients in Echinacea. The polysaccharides obtained from Echinacea mainly include xylose-glucose polysaccharides, inulin, xylan, pectin-like polysaccharides, etc. Among them, the highest content is inulin, which is mainly composed of six monosaccharides such as rhamnose, sorbitol, and xylose [2]. several studies have reported that the polysaccharides and glycoproteins in echinacea have significant immunomodulatory effects. Jia Qinghui [3] proved in vitro that echinacea polysaccharides can enhance the phagocytic capacity of macrophages. Wang Xiaoshan et al. [4] found that echinacea polysaccharides can promote the proliferation of rat small intestinal epithelial cell line IEC-6 through the MTT method, thereby exerting a protective effect on intestinal mucosal absorption and regulating immunity. Some researchers have found through experiments that Echinacea polysaccharides and glycoproteins can significantly increase the serum TNF-α and peripheral blood CD4+ and CD8+ T lymphocyte content of chicks, and are an extremely effective immune enhancer [5].

1.2 Caffeic acid derivatives

Caffeic acid derivatives (CADs) are the main polar components of the active ingredients in Echinacea purpurea. They are the metabolites of caffeic acid esters and cinnamic acid esters, which are based on caffeic acid as the active structural unit. So far, researchers have isolated and identified 18 CADs from Echinacea extracts, including caffeic acid, chlorogenic acid, chicoric acid, isochlorogenic acid, mono-caffeoyl-tartaric acid, echinacoside, and articholic acid [6]. The aboveground parts and roots of Echinacea mainly contain chicoric acid and caffeic acid. The content of chicoric acid in the flowers and roots is higher than that in the stems and leaves. Echinacea purpurea has the least amount of chicoric acid, but it contains 1, 3-caffeoylquinic acid and 1, 5-caffeoylquinic acid, which are not found in Echinacea purpurea. Chicoric acid has immunostimulatory effects and also has some antiviral activity. It can inhibit hyaluronidase and prevent free radicals that degrade collagen from affecting it. Studies have shown that the chicoric acid in echinacea has a significant anti-respiratory syncytial virus effect and is more effective than the treatment drug ribavirin [7].

A variety of caffeic acid derivatives have been successively isolated and identified from echinacea leaves. Caffeic acid, chicoric acid and chlorogenic acid are the main phenolic acid components in Echinacea extracts, with chicoric acid being the most abundant. It is often used as an indicator component, followed by caffeic acid and chlorogenic acid. The content of total phenolic acids and indicator components in Echinacea extracts varies depending on the place of origin, mainly due to differences in the growth environment of the medicinal herbs, as well as during the harvesting, drying and storage processes. Wu Jianming et al. [8] studied the effects of three immunologically active ingredients in Echinacea purpurea on ConA-stimulated lymphocyte proliferation and their secretion of the immune factors interleukin-2 (IL-2) and interferon-γ (IFN-γ) by using normal mouse lymphocyte culture technology combined with MTT and ELISA methods. The results showed that all three types of ingredients could enhance the proliferative capacity of ConA-stimulated mouse splenic lymphocytes. with the caffeic acid derivative having the most significant effect.

1.3 Alkylamides

Alkylamides are the most common lipophilic compounds among the active ingredients of Echinacea. They are present in very small quantities in the plant and are difficult to isolate. The alkyl amides contained in echinacea mainly include dodeca-2E, 4E, 8Z, 10E/Z-tetraenoic acid isobutylamide and 31 other types [9].

The alkylamide components in echinacea were first studied in order to find a substance with insecticidal activity that had an unsaturated fatty acyl amide structure with 4 or 5 carbon atoms in the alkyl group [2].

It was found that the wax amides contained in Echinacea purpurea are inhibitors of the key enzymes in prostaglandin production (cyclooxygenase and 5-lipoxygenase). Researchers have shown that the prostaglandin inhibitor indomethacin stimulates NK cells in mice with leukemia and enhancing the immune function of mice [10]. GOEL V et al. [11] examined the immunomodulatory effects of three components with different dose levels isolated and purified from Echinacea purpurea: chicoric acid, polysaccharides and alkylamides. The results showed that alkylamides significantly increased the phagocytic activity and phagocytic index of alveolar macrophages, and that the immunomodulatory effect was more pronounced in the lungs than in the spleen.

2 Mechanism of immunomodulatory action

2.1 Regulates the growth and development of immune organs

The thymus and spleen are important immune organs in animals, and their developmental status to a certain extent represents the development and growth status of the body's immune system. The development status of immune organs affects the body's immunity. Xu Xin [12] found through an experiment with Salmonella typhimurium infection that Echinacea extract can enhance the expression of non-specific immune genes in mice, increase antibody secretion, promote the growth and development of their spleens, significantly increase the spleen index of normal mice, and thus enhance the body's immune system. Niu Xiaofei et al. [13] found through experiments that Echinacea extract can promote the development of the thymus and spleen in immunosuppressed mice and resist the atrophy of immune organs caused by cyclophosphamide.

Hu Shihui et al. [14] found that Echinacea purpurea formula can significantly increase the thymus, spleen and bursa of Fabricius indices, and promote the development of immune organs. Li Wan et al. [15] found that the high-dose group of Echinacea purpurea extract can significantly increase the spleen index of mice, and the thymus index of mice in the high, medium and low dose groups is also increased, and the high and medium dose groups can also increase the HC50 value of mice. Anne et al. [16] found in their experiments that Echinacea purpurea extract can significantly increase the thymus index and bursa of Fabricius index of broilers, enhancing the body's immune function. Song Hongwei et al. [17] found that Echinacea purpurea extract can promote the growth and development of the bursa of Fabricius, the central immune organ of chicks, while also protecting the B lymphocytes in it and significantly increasing their antibody levels.

2.2 Improves the immune function and biochemical indicators of blood

Researchers have found that both low and high doses of Echinacea immunological drops can significantly stimulate the angiogenic activity of splenic lymphocytes in an immunological angiogenesis experiment [18]. Erythrocytes are extremely important players in the immune response of the blood. They can activate complement system and complement receptors of natural immune molecules, immune adhesion, capture pathogens. There are many natural immune molecules on the membrane of red blood cells, which are also receptors for pathogens. They can directly recognize and capture pathogens, deliver pathogens to other natural immune cells and T and B lymphocytes, and activate the immune response. Gao Xian et al. [19] found that adding Echinacea to feed can significantly increase the concentration of specific antibodies to porcine reproductive and respiratory syndrome virus (PRRSV) and IgM in piglets' serum.

Serum proteins are often used as indicators of the body's immune function and protein metabolism levels. Immunoglobulin Y (IgY) accounts for the largest proportion of human plasma gamma globulins and can promote the phagocytic ability of mononuclear macrophages, thereby regulating the body's immune function. Li Wan et al. [15] experimentally demonstrated that Echinacea purpurea extract not only improves the function of the spleen and thymus in normal mice, but also increases the level of serum hemolysin (IgM and IgG). It has the effect of enhancing cellular and humoral immunity, and is equally effective in mice with low immune function. It also has a significant effect, and there is a certain dose-effect relationship between the two immunomodulatory effects.

2.3 Regulating immune cell function

The currently known mechanisms by which Echinacea extract regulates immune cell function include stimulation of phagocytic activity and macrophage activation and enhancement of NK cell activity, activation of the innate immune system; mitogen-stimulated lymphocyte proliferation and specific antibody production are also enhanced, suggesting that the mechanism may also activate the adaptive immune system.

2.3.1 Effect on lymphocytes

Lymphocytes are an important cellular component of the body's immune response. Echinacea extract can significantly stimulate the LIA activity of mouse splenic lymphocytes, enhancing the body's immune capacity. GABRIELE B M et al. [20] demonstrated through experiments that echinacea can significantly increase T lymphocytes in the spleen and can be used as an immune stimulant. Experiments have found [21] that after Echinacea administration, the cytokines released by macrophages in the peripheral blood of mice activate the proliferation of helper T cells, which can immunologically activate radiation protection and be used as a radiation protective agent. Ma Shaoming et al. [22] found that a certain amount of Echinacea complex can significantly increase the transformation rate of peripheral blood lymphocytes in piglets and significantly increase the antibody level of the vaccine against respiratory and reproductive disorders in pigs.

NK cells are effector lymphocytes with cytolytic activity that can secrete immune regulatory factors. Unlike T/B lymphocytes, NK cells have the characteristics of both innate and adaptive immunity. Numerous experimental results have shown that Echinacea purpurea extract can promote the proliferation of natural killer (NK) cells and monocytes in the bone marrow of normal mice and their main functional organ, the spleen, and increase the number of NK cells in the spleen of mice with leukemia. In vitro experiments have shown that Echinacea purpurea activates NK cell subsets by enhancing their ability to bind to targets and killing bound target cells [23].

2.3.2 Effect on monocytes/macrophages

Echinacea has an IFN-like effect, can activate macrophages, induce the production of IL-1 and IFN, and also stimulate macrophages to release cytokines, which in turn stimulate the proliferation of helper T cells. Echinacea is a good immune activator, which can strongly activate the immune response of macrophages without causing cell damage, quickly produce an immune response to invading pathogens, and enhance cellular immune function [24].

Echinacea extract can activate the innate immune response and initiate a signal cascade in macrophages through TLR4-dependent and non-dependent mechanisms, activating proteins in the cell's mitogen-activated protein kinases (MAPK) signal pathway, such as extracellular regulated protein kinase (ERK), p38 and c-Jun N-terminal kinase (JNK) [25]. MAPK) signal pathway related proteins, such as extracellular regulated protein kinase (ERK), p38 and c-Jun N-terminal kinase (JNK), are activated, ultimately activating nuclear factor-κB (NF-κB), stimulating IL-6, TNF, IL-12 and NO production by in vitro macrophages, thereby upregulating macrophage function. FU A K et al. [25] found that Echinacea purpurea extract polarizes mouse bone marrow-derived macrophages to a classic activated macrophage phenotype by activating the JNK signaling pathway, inducing macrophage activation and antigen presentation, and enhancing immune function. Echinacea purpurea extract has an immunostimulatory effect on mouse macrophages and human peripheral blood mononuclear cells (PBMC), which can stimulate the activation of macrophages and the secretion of derived factors (including TNF-α, IL-1α, IL-1β, IL-6, IL-10 and NO). Yao Lili et al. [26] found in experiments that Echinacea polysaccharides and Echinacea polysaccharides sulfated can regulate the body's immune function by upregulating the concentrations of IL-2 and IL-6 in peripheral blood.

2.3.3 Effect on other immune cells

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that act at the interface between the innate and adaptive arms of the immune system. In response to infection, DCs can promote the generation of an effector CD4+ T helper 1 (Th1) and CD8+ T cell-dominated immune response. For these effector responses, DCs can be directed to become sources of tolerance and increase regulatory T cells (Tregs), thereby controlling effector T cell responses. In addition, DCs can stimulate and control immunity against pathogens as well as tolerance to self-antigens and commensal microorganisms. Echinacea can regulate dendritic cell differentiation and the expression of dendritic cell-specific immune-related genes. ASHMAWY et al. [27] verified in vivo that Echinacea purpurea extract has an immunomodulatory effect on mouse splenic dendritic cells.

2.4 Other

Echinacea purpurea extract can bind to cannabinoid receptor-2 (CB2) as a ligand, activate related signal pathways, and exert its immunomodulatory effect. Research has shown that Echinacea extracts can activate the immune system by binding to the cannabinoid receptor-2 (CB2) and regulating cyclic adenosine monophosphate (cAMP), JNK and p38/MAPK kinase activation are mediated, while the activity of NF-κB and activating transcription factor-2/cAMP-response element binding protein-1 (ATF-2/CREB-1) is increased at the same time. This can open up new avenues for research on echinacea.

Echinacea extract can regulate the expression of genes related to cellular immunity, thereby affecting the function of the immune system. It can trigger the antiviral innate immune pathway, increase the expression of innate immune genes, and enhance the antiviral innate immune gene expression of monocytes through pattern recognition and chemokine-mediated regulation of the IFN signal [29].

3 Conclusion

Echinacea has now become a relatively safe “immune” herb. More and more studies have proven the immune-enhancing effect of echinacea, and the effect is comparable to that of many traditional Chinese medicines that enhance immunity in China. Its outstanding medicinal value has gradually been recognized. Echinacea has been successfully introduced in some areas of China, solving the problem of plant sources and raw materials. In addition, research has gradually been carried out on the chemical composition and activity of domestically produced echinacea, which will lay the necessary foundation for the development and application of domestic Echinacea and the research and development of related drugs. However, there are still some problems with the research on the immune activity of Echinacea: (1) The immune active ingredients in Echinacea work through different immune mechanisms. Due to the differences in extraction methods and the resulting extracts, there are also some differences in the immune effects. The extraction method that maximizes the immune effect of the extract may become the focus of future research. (2) Echinacea has been widely used in clinical practice abroad, but relatively little in China, and the mechanism of action of the clinical effect has not been well described. (3) Due to the lack of advanced cell- and gene-based techniques, the specificity and mechanism of the immune effect of Echinacea need to be further studied and clarified.

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