31.2 Immune System KEY CONCEPT The immune system is a body system that fights infection and prevents illness.

31.2 Immune System Many body systems protect you from pathogens. Many other tissues and systems help the immune system. –Skin: Physically block pathogens from entering the body. –Mucous membranes: Found in the nose and throat; Traps particles before they enter. –The circulatory system: Transports cells of the immune system.

31.2 Immune System Cells and proteins fight the body’s infections. White blood cells attack infections inside the body. –Phagocytes: Cell that engulfs and destroys pathogens. –T cells: Destroys infected body cells. –B cells: Produces antibodies.

31.2 Immune System Three types of proteins fight off invading pathogens. –Complement proteins weaken pathogen membranes. –Antibodies: Protein that causes pathogens to clump or become ineffective. –Interferon: Proteins that stop viruses from reproducing. antibody pathogens

31.2 Immune System Immunity prevents a person from getting sick from a pathogen. In all immunity, pathogens are destroyed before you get sick. Passive immunity occurs without an immune response. Passed through: –mother’s milk –genetics Active immunity is gained after the body undergoes a specific immune response.

31.2 Immune System BOTH Prevent future illness if the body becomes infected! Lytic Infection is an infection pathway in which the host cell bursts, releasing the new viral offspring into the host’s system, where each then infects another cell. In a Lysogenic infection, a phage combines its DNA into the hosts cell’s DNA.