Immunology studies the body's defense systems and how they recognize, control, and remember threats.
The immune system is a network of cells, tissues, organs, and molecules that helps protect the body from harmful microbes and other threats. Immunologists study how these defenses work, why they sometimes fail, and how vaccines and treatments can guide immune responses more effectively.
Skin, mucus, and other barriers help stop many threats before they enter tissues.
Learn MoreFast, general defenses respond quickly when microbes cross the body's barriers.
Learn MoreSpecialized immune cells learn to recognize particular targets.
Learn MoreAntibodies bind specific targets and help the immune system respond to them.
Learn MoreMemory cells can make later responses to familiar threats faster and stronger.
Learn MoreThe immune system must defend the body without attacking harmless substances or its own tissues.
Learn MoreThe body's first defenses are physical and chemical barriers. Skin forms a tough outer shield, while mucus traps particles in the respiratory and digestive systems. Tears and saliva contain substances that can damage some microbes, and stomach acid makes the digestive tract difficult for many organisms to survive. These barriers reduce how often deeper immune defenses are needed.
Innate immunity responds rapidly and recognizes broad patterns shared by many microbes. Cells such as neutrophils and macrophages can engulf invading organisms, while other immune signals trigger inflammation and help recruit more defensive cells to an affected area. Fever can also support the body's response. Innate defenses act quickly, but they do not provide the highly specific recognition associated with adaptive immunity.
Adaptive immunity depends mainly on B cells and T cells. Each of these lymphocytes carries receptors able to recognize particular molecular targets. B cells can develop into cells that release antibodies, while several kinds of T cells help coordinate immune responses or destroy infected cells. Adaptive responses usually take longer to develop during a first encounter, but they can become highly targeted.
Antibodies are Y-shaped proteins produced by specialized B cells. Their tips contain variable regions that can bind to specific antigens, which are molecular features recognized by the immune system. Once bound, antibodies may block a pathogen from attaching to cells, clump targets together, or mark them for destruction by other parts of the immune system. Different antibody classes perform different jobs in blood, tissues, and body secretions.
After some infections or vaccinations, long-lived memory B cells and memory T cells remain in the body. If the same threat appears again, these cells can respond more quickly than they did during the first encounter. Vaccines use this feature by safely exposing the immune system to antigens or instructions related to a pathogen, helping the body prepare without requiring the person to experience the full disease first.
A healthy immune system must distinguish dangerous targets from the body's own cells and from harmless substances. When immune control breaks down, several kinds of problems can occur. Allergies involve excessive reactions to normally harmless triggers, while autoimmune diseases involve attacks on the body's own tissues. Immunodeficiency occurs when parts of the immune system are missing or weakened. Studying these conditions helps scientists understand how immune regulation normally works.