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The Immune System (Innate/Nonspecific (2nd Line of Defense Non-specific…

- - - - Complement System: proteins are always in the blood, enhancing inflammation and phagocytosis.
      - Interferon: protein produced by a virus-infected cell that warns cells around it to defend themselves.
      - Cytokines: protein signals released by stressed cells, enhancing inflammation.
      - Defensins: peptides produced by neutrophils. Make holes in bacterial cell walls.
      - Collectins: proteins that provide broad protection against bacteria, yeasts, and some viruses. Enhance phagocytosis by interacting with surface sugars.
- - - - Activation: B cell encounters an antigen that fits its antigen receptors. Antigen: on the surface of a bacterium, like a lock.
      - Antibody: produced by B cell. Binds to antigen on the surface of pathogen. Like a key.
        
        Five Actions of Antibodies:
        
        Opsonization: surround to macrophage can engulf easily.
        
        Agglutination: make cells combine in a mass so they can't function.
        
        Complement fixation: enhance activity of complement system and natural killer cells.
        
        Neutralization: antibodies block binding sites for viruses so they can't enter cell.
        
        Precipitation: like agglutination, but for viruses.
        
        Immune Responses
        
        Primary Response: 1st exposure to new pathogen. Takes a few days to recognize pathogen, manufacture appropriate B cells and antibodies, and respond to infection.
        
        Secondary Response: much faster and stronger response. Some B cells (memory cells) remain after the primary response, and they are quickly cloned. Happens within a day.
      - Humoral Immunity: antibodies operate in fluids.
    - - Cellular Immunity: T cells are cytotoxic or helpers.
      - T cell binds to infected cell. It kills the infected cell and virus contained inside.
      - Activation: processed fragments of the antigen are attached to the surface of an antigen-presenting cell. MHC antigens help T cells recognize foreign cells.