Final answer:
An adjuvant is a substance that enhances the effectiveness of vaccines by increasing the antigenicity of a pathogen, helping to stimulate the immune system to create immunological memory.
Step-by-step explanation:
An adjuvant is a substance that is used to increase the effective antigenicity of a pathogen when used in a vaccine. The purpose of an adjuvant is to enhance the body's immune response to the vaccine, often by stimulating the action of immune cells such as macrophages and dendritic cells. This ensures that the immune system can create a strong and lasting immunological memory, which is crucial for long-term immunity. Adjuvants are commonly used in subunit vaccines, where they help the extracted components of the pathogen to elicit a protective immune response without causing an infection.
Adjuvants may help to reduce the dose of the antigen needed and can also influence the type of immune response to the antigen, promoting either a humoral or a cell-mediated response. This is paramount in the design of vaccines against a variety of diseases, including infectious diseases and cancer.