Chemical nature and classification
Most adjuvants are substances completely foreign to the human or animal body. They vary greatly in origin and structure. The main groups used in vaccine development:
- Mineral sorbents: aluminum hydroxide gels and aluminum phosphate.
- Bacterial components: extracts from BCG bacteria (which serve as the basis for the classical Freund's adjuvant), as well as inactivated pertussis pathogens.
- Complex chemical compounds: lipopolysaccharides (LPS), protein-lipopolysaccharide complexes, as well as muramyl dipeptide and its derivatives.
- Lipids and emulsifiers: lanolin, Arlacel.
- Inflammation-provoking substances: turpentine, saponin.
- Polymeric compounds.
Mechanism of action: effect on the antigen
The action of adjuvants is always complex. Their first direction of action is the physicochemical alteration of the antigen itself with which they are mixed.
Due to sorption or the formation of chemical bonds with a polymeric carrier, enlargement of the molecule occurs. Soluble antigens are converted into a particulate state (change shape). This structural change has an important immunological consequence: the enlarged particulate antigen is much more efficiently captured and presented by phagocytic and immunocompetent cells. Moreover, the use of adjuvants can transform the nature of the immune response, turning a thymus-dependent antigen into a thymus-independent one.
Mechanism of action: effect on the macroorganism
The second direction of the adjuvant's action is direct impact on the body tissues into which the vaccine is injected. Vaccines containing such additives are commonly referred to as depot vaccines.
In response to the administration of a foreign and often irritating substance at the injection site, a local inflammatory reaction develops, culminating in the formation of a fibrous capsule. A so-called depot is created, in which the antigen persists for a long time.
The gradual, fractional release of the antigen from this depot into the systemic circulation provides the summation effect. For the immune system, this works like repeated irritation, replacing the need for frequent revaccinations.
Additionally, adjuvants provide direct immune stimulation: they directly activate the proliferation of immunocompetent cells and enhance the synthesis of specific protective proteins.
Application efficacy
The use of adjuvants makes it possible to enhance antigen immunogenicity several-fold overall. However, the most pronounced specific effect is observed when working with toxoids.
According to A.A. Vorobyov, when using soluble molecular protein antigens (such as tetanus, botulinum, or diphtheria toxoids), the addition of the correct adjuvant increases the preparation's immunogenicity up to 100-fold compared to the administration of the "pure" antigen.
Briefly: answers to topical questions
What are the components of Freund's complete adjuvant?
Freund's complete adjuvant contains the components of incomplete adjuvant and mycobacteria.
- Mineral oil is the lipid base.
- Lanolin is the lipid component.
- Emulsifier is a substance used to create an oil emulsion.
- BCG (Mycobacterium bovis) is a vaccine strain of mycobacteria, the addition of which ensures effective induction of the primary immune response and stimulation of innate immunity cells.
Through which cell receptors do adjuvants directly stimulate immunocompetent cells?
Adjuvants directly stimulate immune cells via pattern recognition receptors (PRRs):
- Membrane receptors — TLRs located on the cell surface and in endosomes, as well as CLRs.
- Cytosolic receptors — NOD1, NOD2, RIG-I, MDA5, and DAI.
Which specific polymeric compounds are used as adjuvants in modern vaccines?
In modern vaccines, harmless synthetic polymers are used as adjuvants and high-molecular-weight carriers.
- Polyvinylpyrrolidone is a polymer that functions as an antigen transporter and an adjuvant simultaneously.
- Polyoxidonium is a polymeric immunomodulator conjugated with an antigen. It is used in the development of influenza vaccines and is also utilized in domestic HIV vaccines currently under development.
To remember the directions of adjuvant action, the acronym EDS can be used: Enlargement (effect on antigen), Deposition (retention in tissues), Stimulation (activation of immune cells).
Class and exam questions
What is the purpose of adjuvants in vaccines?
They non-specifically enhance the immunogenicity of an antigen, making the immune response more pronounced and prolonged.
What are depot vaccines?
These are vaccines with added adjuvants that induce the formation of a fibrous capsule at the injection site. From this "depot", the antigen is released gradually, creating the effect of continuous revaccination.
Which preparations do adjuvants work best on?
They are most effective when combined with soluble protein antigens (toxoids) — diphtheria, tetanus, and botulinum. Their immunogenicity can increase up to 100-fold.
What else to study on this topic
- Features of fibrous capsule formation in response to adjuvants
- Mechanism of transformation of a thymus-dependent antigen into a thymus-independent one
- Application of BCG extracts and Freund's adjuvant
- The role of muramyl dipeptide in immune activation
Study the full topic in the «Microbiology» course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Adjuvants" and 4,383 other subject pages
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 141 video lectures on the subject
Other topics in the «Immunoprophylaxis Agents» section
Free video lessons: microbiologyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.