The Immune System THE Body’s Defense Systems

Nonspecific Defenses First Line of Defense Skin Antimicrobial proteins Mucous membranes Cilia Gastric juice Symbiotic Bacteria Temperature

Nonspecific Defenses Second Line of Defense Inflammatory Response – Injury breaking the skin introducing pathogens Histamine is released causing increase blood flow to area – Causes redness, swelling, warmth, and pain Vasodilation (dilation of the blood vessels) – Caused by histamine Phagocytes pass through capillary walls into tissues to ingest and destroy pathogens

Nonspecific Defenses Second Line of Defense Phagocytes destroy the pathogens and the injury begins to heal. – Neutrophil; Macrophage Natural killer cells – Attack pathogen-infected cells – Effective at killing cancer cells and virus- infected cells

Nonspecific Defenses Second Line of Defense Complement – A group of about twenty proteins that “complement” defense reactions. – Help to destroy foreign or infected cell by promoting cell lysis Interferon – Molecules secreted by viral infected cells that stimulate neighboring cells to produce proteins that help them defend against viruses

Specific Defenses Third Line of Defense A response aimed specifically at the pathogen Lymphocyte = white blood cell of the immune system React to antigens Two types – B cells Made in the bone marrow A part of the humoral immune response Produce antibodies Plasma cell- B cells that release specific antibodies Memory cell- long-lived B cells that do not release their antibodies, they circulate in the body and respond quickly to eliminate any subsequent invasion by the same antigen.

Specific Defenses Third Line of Defense A response aimed specifically at the pathogen – T cells Made in the bone marrow, mature in the Thymus (T for thymus) A part of the cell-mediated response – Destroy infected cells Cytotoxic T cells (killer T cells); Helper T cells; Suppressor T cells

Comparing Immune Responses Type of cellFunction MacrophageEngulfs and kills pathogens NeutrophilEngulfs and destroys pathogens Natural killer cellPunctures infected cells Helper T cellActivates cytotoxic T cells Cytotoxic T cellPunctures labeled infected cells B cellLabels invaders for destruction by macrophages Plasma cellReleases antibodies Memory cellStores information about a pathogen