Innate Immune System

Innate/nonspecific immunity
1. Nonspecific defense that is always active against infection, but lacks ability to target specific invaders
  1. Skin (integument)
    1. Defensins
      1. Antibacterial enzyme
    2. Basic physical barrier against the outside world
  2. Respiratory system
    1. Lysozyme
      1. Nonspecific bacterial enzyme secreted in saliva and tears
    2. Cilia
      1. Mucous membranes that trap particulates and push them to the oropharynx to be swallowed or expelled
2. Gastrointestinal tract
  1. Acid eliminates most pathogens.
  2. Gut bacteria
    1. Many invaders cannot compete with present gut flora, and therefore die off.
3. Complement system
  1. Classical pathway
    1. Requires binding of antibody to pathogen
  2. Alternative pathway
    1. Doesnt require antibodies
  3. Nonspecific defense proteins in blood. Punch holes in bacteria cell walls (osmotic instability). Cannot be modified to target specific organisms
4. Interferons
  1. Proteins that prevent viral replication and dispersion
  2. Decrease permeability of nearby cells making it harder for virus to infect.
  3. Upregulate MHC class I and II
  4. Responsible for flu-like symptoms
5. Cells of the innate immune system
  1. Monocytes
    1. Macrophages
      1. Antigen presenting cell. When a bacterial invader enters a macrophage-resident tissue, macrophages: 1. Phagocytose invader through endocytosis. 2. Digests invader using enzymes. 3. Present peptides (antigen) of invader (using MHC) to adaptive immune system
      2. Major Histocompatibility Complex
        MHC Class I pathway
        Endogenous pathway (displays proteins from within the cell). Present in all nucleated cells. Displays to cytotoxic (CD8) cells
        MHC Class II pathway
        Present on macrophages, dendritic cells, and some B-cells (adaptive). Displays exogenous antigens (originate outside the cell) to T-helper cells (CD4)
        Displays antigens to adaptive immune system.
      3. Pattern recognition receptors (PRR)
        Toll-like receptors
        Most common PRR. Single, membrane-spanning, non-catalytic receptors
        Able to recognize category of invader (bacteria vs. virus vs. fungi, etc). Aids in production of appropriate CYTOKINES
        Cytokines
        Chemicals that stimulate inflammation and recruit additional immune cells
    2. Blood-borne
  2. Antigen Presenting cells
    1. Dendritic Cells
      1. Antigen presenting cells in the skin
    2. B cells (adaptive immunity)
  3. Natural killer cells
    1. Nonspecific lymphocyte. Can detect down regulation of MHC (brought on by certain pathogen defenses) and induce apoptosis in virally infected cells. Can offer protection against growth of cancer as well
  4. Granulocytes
    1. Neutrophils
      1. Leukocyte. Short lived (5 days). Phagocytic (particularly opsonized bacteria)
      2. Chemotaxis
        Method by which neutrophils can follow bacteria
      3. Pus
        Dead neutrophils form pus
    2. Eosinophils
      1. Primarily involved in allergic reactions and parasitic infections .
      2. Histamine
        Inflammatory mediator. Vasodilation & increased blood vessel leakiness allows other immune cells to disseminate
    3. Basophils
      1. Mast Cells
        Smaller granules than basophils. Exist in tissue, mucosa, epithelium. Degranulation (exocytosis of granule contents) occurs when antigen binds to mast cell, causing histamine release, leading to inflam/allergic rxn
        Basophils and mast cells also release HISTAMINE in response to allergens
      2. Large purple granules. Least populous under normal conditions

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Innate Immune System

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	Created by One Health over 9 years ago