Immune System

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Immune System
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Acquired VS Innate Immunity

• Innate Immunity- broad and non-specific
• Includes skin, mucus and macorphages
• Skin is an impenetrable barrier, and mucous
  covers any openings that may be vulnerable. Skin
  also has secretions that are low in pH and
  contain enzymes that inhibit bacterial growth.
• Acquired Immunity- develops after exposure to a
  pathogen it is highly specific and uses
  lymphocytes (B and T) that cause either humoral
  or cell mediated defense.

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Cells of the innate immune system
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Other Chemical Defenses

• Complement System- 30 serum proteins that are
  activated in an infection and causes microbes to
  lyse.
• Interferon-Defend against viral infections. They
  are secreted by infected cells that cause
  neighboring cells to produce substances that
  inhibit viral reproduction. Some activate
  macrophages.
• Natural Killer (NK) Cells- attack virus-infected
  or cancer cells by releasing chemicals that make
  the cell undergo programmed cell death.

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Inflammatory Response

• Tissue is injured? Chemical signals histamine
  from cells in connective tissue, prostaglandins
  and chemokines (chemicals that direct the
  migration of phagocytes) that dilate and increase
  the permeability of capillaries to deliver
  clotting factors and leukocytes to the injury.
• May lead to a systemic response including mass
  release of leukocytes and fever. Too much of a
  systemic response is septic shock.

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Acquired Immunity- Lymphocytes

• Cytokines help activate the lymphocytes of the
  immune system in response to an antigen.
• Antigen- usually a large molecule that a
  lymphocyte recognizes and binds to. The binding
  portion of an antigen is called an epitope.

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Lymphocytes B and T Cells

• Both circulate in the blood and have antigen
  specific receptors
• B Cells- have receptors that are Y shaped and
  made of 2 light chains and 2 heavy chains. One
  side of the chain is anchored in the membrane and
  the other is in the cytoplasm They have a
  variable region that is specific to an antigen.
  They only recognize intact antigens and develop
  in the bone marrow.
• T Cells- have alpha and beta chains and a
  variable region. They can recognize fragments of
  antigens that are bound to the Major
  Histocompatibility Complex (MHC). Develop in the
  thymus.

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Acquired Immunity

• Lymphocyte finds an antigen with an epitope
  matching its receptors.
• Lymphocyte divides making effector cells and a
  memory cells.
• Primary response- make many b and t cells and
  plasma cells (10- 17 days). Another exposure
  will cause a secondary response with memory
  cells. The secondary response is much more rapid
  than primary (2-7 days).

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T Cell Receptors For Antigens

• Major Histocompatibility Complex (MHC)- present
  fragments of antigens on the surface of a cell
• MHC I- found on most nucleated cells of the body
• MHC II- found on dendritic cells, macrophages and
  B cells
• MCH complexes also determine self.
• Surface proteins
• CD8- found on cytotoxic T cells that aid in
  binding the target cell to the cytotoxic T cell
• CD4- found on helper T cells and help them bind
  to MHC II complex to activate them.

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Humoral Response

• Bacteria or Foreign Invader
• Antigen is engulfed and displayed by dendritic or
  macrophage cells.
• B cells are activated by helper T cells that bind
  to antigens. They are activated by cytokines.
• An activated B cell/helper t-cell takes up and
  degrades the bacterium and displays class II
  MHC-peptide-antigen complex. This activated B
  cell proliferates into memory B cells and
  antibody secreting plasma cells. The antibodies
  are antigen specific.

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Antibodies and their Role

• Antibodies aid in viral neutralization
• Increase binding
• Clumping
• Phagocytosis
• Initiating the complement system

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Name and Description Antibody of Complexes

• IgA Found in mucosal areas, such as the gut,
  respiratory tract and urogenital tract, and
  prevents colonization by pathogens. Also found in
  saliva, tears, and breast milk.
• IgD Functions mainly as an antigen receptor on B
  cells that have not been exposed to antigens. Its
  function is less defined than other isotypes.
• IgE Binds to allergens and triggers histamine
  release from mast cells and basophils, and is
  involved in allergy. Also protects against
  parasitic worms.
• IgG In its four forms, provides the majority of
  antibody-based immunity against invading
  pathogens. The only antibody capable of crossing
  the placenta to give passive immunity to fetus.
• IgM Expressed on the surface of B cells and in a
  secreted form with very high avidity. Eliminates
  pathogens in the early stages of B cell mediated
  (humoral) immunity before there is sufficient
• From wikipedia

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Cell Mediated Response

• Used in defense against Viruses and Cancer
• Helper T-Cells recognize Class II MHC and becomes
  an activated Helper T Cell. Activated helper T
  cells secrete cytokines that activate cytotoxic T
  cells and memory T cells.
• Cytotoxic T cells bind to class I MHC-antigen
  complex with the help of CD8, and cytotoxic T
  cells release molecules which are taken up by the
  target cells and initiate cell death.

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How can immunity be achieved artificially?

• Immunization- creates memory cells
• Passive immunity- giving antibodies

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Immune System Malfunctions

• Allergies- artificial histamine release
• Lupus- breaks down body cells because it cant
  detect self.
• Arthritis- break down of cartilage
• MS- attacks myelin

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AIDS

• Destroys helper T cells which stops both humoral
  and cell mediated responses.