Immune System

1. Immune System

2. Innate immunity is present before any exposure to pathogens and is effective from the time of birth • It involves nonspecific responses to pathogens • Innate immunity consists of external barriers plus internal cellular and chemical defenses • Key internal defenses are macrophages and other phagocytic cells

3. Acquired immunity, or adaptive immunity, develops after exposure to agents such as microbes, toxins, or other foreign substances • It involves a very specific response to pathogens • Recognition is by white blood cells called lymphocytes • Some lymphocytes produce antibodies; others destroy infected cells, cancer cells, or foreign tissue

4. LE 43-2 ACQUIRED IMMUNITY Slower responses to specific microbes INNATE IMMUNITY Rapid responses to a broad range of microbes External defenses Internal defenses Skin Phagocytic cells Humoral response (antibodies) Mucous membranes Antimicrobial proteins Secretions Inflammatory response Invading microbes (pathogens) Cell-mediated response (cytotoxic lymphocytes) Natural killer cells

5. Microbes Pseudopodia LE 43-4 MACROPHAGE Vacuole Lysosome containing enzymes

6. Natural Killer Cells • Natural killer (NK), also known as Cytotoxic T Cells, cells attack virus-infected body cells and cancer cells • They trigger apoptosis in the cells they attack

7. Cell-mediated immune response Humoral immune response First exposure to antigen LE 43-14_3 Antigens displayed by infected cells Antigens engulfed and displayed by dendritic cells Intact antigens Activate Activate Activate Secreted cytokines activate B cells Cytotoxic T cell Helper T cell Gives rise to Gives rise to Gives rise to Active and memory helper T cells Memory cytotoxic T cells Active cytotoxic T cells Plasma cells Memory B cells Defend against infected cells, cancer cells, and transplanted tissues Secrete antibodies that defend against pathogens and toxins in extracellular fluid