Your body has different ways to protect you against disease-causing invaders.

• 26.1 Three lines of defense prevent and fight pathogen attacks.
• 26.2 External barriers prevent pathogens from entering your body.
• 26.3 The non-specific division of the immune system recognizes and fights pathogens and signals for additional defenses.
• 26.4 The non-specific system responds to infection with the inflammatory response and with fever.

Specific immunity develops after exposure to pathogens.

• 26.5 The specific division of the immune system forms a memory of specific pathogens.
• 26.6 The structure of antibodies reflects their function.
• 26.7 Lymphocytes fight pathogens on two fronts.
• 26.8 Clonal selection helps in fighting infection now and later.
• 26.9 This is how we do it: Does contact with dogs make kids healthier?
• 26.10 Cytotoxic T cells and helper T cells serve different functions.

Malfunction of the immune system causes disease.

• 26.11 Autoimmune diseases occur when the body turns against its own tissues.
• 26.12 AIDS is an immune deficiency disease.
• 26.13 Allergies are an inappropriate immune response to a harmless substance.