The immune system is a complex network of cells, tissues, and organs that work together to defend the body against infection and disease.

The adaptive immune response is responsible for recognizing and attacking specific pathogens through the production of antibodies and activation of T cells.

Antibodies are proteins produced by B cells that recognize and bind to specific antigens on pathogens, marking them for destruction.

T cells are responsible for killing infected cells and activating other immune cells to mount an immune response.

Macrophages are phagocytic cells that engulf and destroy pathogens, cellular debris, and foreign substances.

Active immunity is acquired through exposure to pathogens, which stimulates the immune system to produce antibodies and T cells. Passive immunity is acquired through exposure to antibodies, which provide temporary protection against specific pathogens.

Herd immunity is the immunity of a population to a disease, which occurs when a large proportion of the population is immune, either through vaccination or previous infection, providing indirect protection to those who are not immune.

Vaccines are used to prevent diseases by stimulating the immune system to produce antibodies and T cells against specific pathogens, providing protection against future infection.

Pathogens are microorganisms that cause disease in their host, while commensals are microorganisms that live in or on the host without causing harm and may even provide benefits.

The complement system is a group of proteins that work together to help antibodies destroy pathogens by forming a membrane attack complex that punctures the pathogen's cell membrane.

Cytokines are small proteins that are produced by immune cells and act as chemical messengers to activate other immune cells and regulate the immune response.

The lymphatic system is a network of vessels and nodes that transports immune cells throughout the body, allowing them to circulate and respond to infections and foreign substances.

The thymus is an organ where T cells mature and become functional, gaining the ability to recognize and attack pathogens.

The spleen is an organ that stores and releases immune cells, such as lymphocytes and macrophages, which help to fight infection and disease.

The bone marrow is responsible for producing immune cells, including B cells, T cells, and macrophages, which play crucial roles in the immune response.