What type of immunity is produced by exposure to an antigen and leads to long-term immunity?

Active immunity is produced when the immune system is exposed to an antigen and subsequently generates a response, which includes the production of antibodies specifically tailored to that antigen. This type of immunity can occur naturally through infection or artificially through vaccination.

When the body encounters an antigen, it stimulates the activation of specific immune cells, such as T and B lymphocytes. These cells remember the antigen, allowing for a faster and more effective response if the same pathogen is encountered again in the future. As a result, active immunity leads to long-term protection against diseases due to the formation of memory cells.

In contrast, passive immunity involves the transfer of antibodies from one individual to another, providing immediate but temporary protection. This can occur naturally, such as when antibodies are transferred from a mother to her baby during breastfeeding. Innate immunity is the body's first line of defense and is not specific to particular pathogens, while acquired immunity refers broadly to immunity developed through exposure, but it is often used interchangeably with active immunity, which specifically emphasizes the role of the immune system's response to antigens.