Acquired immunity, also known as adaptive immunity, is a specific immune response that develops after exposure to a pathogen or antigen. This type of immunity is different from innate immunity, which is present at birth and provides immediate but non-specific defense against pathogens. Acquired immunity is a key component of the immune system and plays a crucial role in protecting the body from various diseases.

Acquired immunity can be classified into two main types:

Active immunity is the result of the body's own immune response to an antigen. It can occur naturally through infection or artificially through vaccination. When the immune system encounters an antigen, such as a pathogen or a vaccine, it triggers an immune response that leads to the production of specific antibodies and memory cells. These memory cells remember the antigen and provide long-lasting protection against future infections.

Passive immunity, on the other hand, is the transfer of pre-formed antibodies from one individual to another. This can occur naturally through the transfer of maternal antibodies to a developing fetus or artificially through the administration of antibodies derived from another individual or animal. Passive immunity provides immediate, but temporary protection, as the transferred antibodies are gradually eliminated from the recipient's body.

Acquired immunity involves several mechanisms that work together to provide an effective immune response:

Antibodies, also known as immunoglobulins, are proteins produced by B cells in response to the presence of antigens. Antibodies bind to specific antigens and help neutralize or eliminate them from the body. They can block the entry of pathogens, mark them for destruction by other immune cells, or activate other parts of the immune system.

Memory cells are specialized B and T cells that remember specific antigens encountered during an initial infection or vaccination. These cells allow for a faster and more efficient immune response upon subsequent exposures to the same antigen. Memory cells play a crucial role in providing long-lasting protection against recurrent infections.

Helper T cells, also known as CD4+ T cells, play a central role in coordinating the immune response. They recognize antigens presented by antigen-presenting cells (APCs) and help activate other immune cells, such as B cells and cytotoxic T cells. Helper T cells also secrete cytokines that stimulate immune responses and regulate the function of other immune cells.

Cytotoxic T cells, also known as CD8+ T cells, are responsible for eliminating infected or abnormal cells. These cells recognize and destroy cells that display antigens derived from intracellular pathogens, such as viruses or intracellular bacteria. Cytotoxic T cells play a crucial role in clearing viral infections and eliminating cancer cells.

Acquired immunity is essential for protecting the body against a wide range of pathogens and preventing recurrent infections. It provides long-lasting immunity and allows for a faster and more effective response to future exposures. Vaccinations, which stimulate active immunity, have played a crucial role in controlling and eradicating many infectious diseases. Understanding acquired immunity helps in developing strategies for disease prevention, treatment, and the development of new vaccines.