A brief talk on what is an adjuvant

  • What is an adjuvant?

    Adjuvants, also known as immunomodulators or immunoenhancers, refer to a class of substances that can nonspecific change or enhance the specific immune response of the body to the antigen prior to or when mixed with or injected into the animal body at the same time.

    Adjuvants can enhance the immunogenicity, immune response speed and tolerance of antigens, regulate the affinity and specificity of antibodies to antigens, stimulate cell-mediated immunity, and promote the absorption of vaccines in gastrointestinal mucosa. Little is known about the mechanism of adjuvants, which hinders the design of Autoimmune Disease Vaccine. The adjuvants often activate multiple immune chains. Only a few of them are related to antigen-specific responses. It is difficult to know exactly the role of adjuvants.

    Adjuvants can increase the infiltration of cells, prevent antigen degradation, transport antigens to specific antigen presenting cells (APC5), enhance the presentation of antigens or induce the release of cytokines. After injection of antigen, the antigen can be absorbed directly by APC5, which binds to or degrades the surface antibody of B cells. The way of antigen absorption mainly depends on the characteristics of Biomarker Development, but it is also affected by adjuvants. Antigens absorbed by APC5 are presented on CD8 + or CD4 + T cells through MHCI or MHCII in two ways. According to the different ways of secreting cytokines after vaccination, it can be divided into Th1 response and Th2 response. Th1 response is mainly induced to secrete IFN-gamma, IL-2 and IL-12, while Th2 response is induced to secrete IL-4, IL-5, IL-6 and IL-12. Different cytokine secretion patterns are mutually antagonistic. Promoting one form of response often inhibits another. IgG2a antibody production is considered to be Th1 response. However, induction of IgG1 is often associated with Th2 response. Different adjuvants can induce similar antibody levels, but the way of cytokine response may be different. Th1 or Th2 response mode has a significant impact on the efficacy of the vaccine.

    According to published literature, there are about hundreds of new adjuvants. Different adjuvants have different mechanisms to promote immune response. It is not easy to classify these adjuvants ideally. They can be classified according to their mechanism of action, such as adsorbing antigen, granular adjuvant, immunoregulatory factors, etc. However, some adjuvants have different functions at the same time, so they can also be classified according to their sources, such as plant, bacterial, synthetic, organic and inorganic salts, etc. However, some adjuvants are prepared from different sources.

    There are many kinds of adjuvants and the effect is true, but they also have some inevitable disadvantages, such as oil adjuvants have some problems, such as viscosity, stability and local reaction of injection, AL (OH) 3 is not enough to induce weak antigen immune response and cell-mediated immunity, silica particle adjuvants cause pigmentation and cancer vaccine, and the stability of liposomes needs to be improved. The mechanism of B acting as an adjuvant is not clear. Other adjuvants, due to their cumbersome preparation, high price and unstable effect, limit their promotion and use. The ideal adjuvant is to induce appropriate immune stimulation with minimal immune stimulation without adverse reactions.

    The main trend of research on immune adjuvants is to develop low-cost, high-efficiency, quick-acting and long-acting new adjuvants from multiple sources and channels, and to explore the mechanism of action of the new adjuvants. Polysaccharides have been extensively studied as drugs to enhance the immune function of the organism, while the studies as immune adjuvants are limited to microbial-derived lipopolysaccharides and glucose. In fact, polysaccharides are very important bioactive substances. Some polysaccharides can regulate the levels of lymphocyte, carrier protein, interleukin and antibody to enhance immune function. Some polysaccharides can be chemically modified to form porous micro-particles, which can concentrate and store antigens. Polysaccharide particles can tolerate the degradation of gastrointestinal tract and develop into oral immune carriers. Therefore, using polysaccharides as adjuvants can not only enhance immune function, but also have the adjuvant activity of carrying antigens and promoting antigen extraction, which is a new trend of research adjuvants.

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