From the Guidelines
Adjuvants in vaccines primarily act at the site of injection and in the local lymph nodes, not within cells themselves. When a vaccine is administered, adjuvants create a depot effect at the injection site, where they interact with immune cells like dendritic cells and macrophages. These cells recognize the adjuvant as a danger signal, which triggers their activation and migration to nearby lymph nodes. Adjuvants enhance immune responses by promoting antigen uptake, processing, and presentation on the cell surface (not inside the cell), stimulating pattern recognition receptors on cell membranes, and creating an inflammatory environment that recruits more immune cells. This process ultimately leads to stronger activation of T and B lymphocytes in the lymph nodes, resulting in more robust and longer-lasting immunity. Common adjuvants include aluminum salts, oil-in-water emulsions, and toll-like receptor agonists, each working through slightly different mechanisms but all functioning primarily in the extracellular space and on cell surfaces rather than inside cells, as noted in studies such as 1. Some studies have also explored the use of adjuvants in specific patient populations, such as those with systemic lupus erythematosus 1 or solid-organ transplant recipients 1, but the primary mechanism of action remains the same. Key points to consider include:
- Adjuvants act locally at the injection site and in lymph nodes
- They interact with immune cells like dendritic cells and macrophages
- Adjuvants enhance immune responses through various mechanisms, including antigen presentation and stimulation of pattern recognition receptors
- Common adjuvants include aluminum salts, oil-in-water emulsions, and toll-like receptor agonists
- The use of adjuvants has been explored in various patient populations, but their primary mechanism of action remains consistent, as supported by studies like 1.
From the Research
Adjuvants in Vaccines
- Adjuvants are used in vaccines to enhance the level and breadth of the immune response to a target antigen, thereby enhancing protection from the associated disease 2.
- They can be categorized as immunostimulants and delivery systems, with immunostimulants leading to the maturation and activation of antigen-presenting cells (APCs) by targeting Toll-like receptors (TLRs) and other pattern recognition receptors (PRRs) 3.
Mechanism of Action
- Adjuvants may act by a combination of various mechanisms including formation of depot, induction of cytokines and chemokines, recruitment of immune cells, enhancement of antigen uptake and presentation, and promoting antigen transport to draining lymph nodes 4.
- They activate innate immune responses to create a local immuno-competent environment at the injection site, which can alter the quality and quantity of adaptive immune responses 4.
- Adjuvants can also prolong antigen exposure to dendritic cells (DCs) and induce their maturation, leading to the activation of antigen-specific T cells 5.