Immune System

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Immune System
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Immune System

• System of chemicals, white blood cells, and
  tissues that protect the body against pathogens
  (disease causing microorganisms)
• Immune system has non-specific and specific
  responses
• Aided by lymphatic system

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Lymphatic System

• Returns fluids leaked from the blood back to the
  blood
• Contains many different types of leukocytes
  involved in the immune response
• Lymphoid organs include lymph nodes, spleen,
  thymus, tonsils, and lymphoid tissue in digestive
  and respiratory tracts
• Lymph nodes filter lymph of pathogens and
  activates immune response against an antigen

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Lymph Node
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White blood cells originate from stem cells in
red bone marrow
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Lines of Defense Against Pathogens

• Nonspecific system
• 1st line of defense (surface membrane barriers)
  
• - skin (keratin) and acid mantle (sweat, sebum)
• - mucous membranes and secretions (saliva,
  tears, mucus, stomach acid, enzymes, urine,
  earwax, nasal hairs, etc.)
• 2nd line of defense (cell and chemical defense)
  
• Phagocytes white blood cells that eat foreign
  matter (ex. Macrophages, dendritic cells)
• Natural killer cells (kill virus infected cells)
• chemicals released from cells and damaged tissues
  (interferon, histamine, complement)
• Inflammation (attracts white blood cells to the
  area and prevents spread of infection) and fever
  (speeds up the activity of white blood cells and
  slows down viral replication)

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Specific (Adaptive) System (3rd line of defense)

• React against a specific antigen (cell membrane
  protein) on the surface of the pathogen.
• Involves B-lymphocytes (humoral immunity) and
  T-lymphocytes (cell-mediated immunity)
• Also involves antigen-presenting cells (APC) like
  macrophages and dendritic cells (ingest pathogen
  and display the pathogens antigens on their
  surfaces)

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B-lymphocytes (B-cells)

• Type of lymphocyte involved in humoral immunity
• Develop into plasma cells which secrete
  antibodies when they recognize an antigen
• Antibodies are made against specific antigens
• Memory B cells are produced after 1st exposure to
  antigen - results in quicker response if the
  person is exposed to the same antigen again

Antibody binding to antigen
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Primary and Secondary Immune Response
Blood antibody level rises more quickly with 2nd
exposure
Memory cells formed
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T cells

• Type of lymphocyte involved in cell-mediated
  immunity
• Cytotoxic T-cells (Tc) kill only cells that are
  infected with a virus
• Helper T-cells (Th) release chemicals called
  cytokines to activate B-cells, cytotoxic T-cells,
  and macrophages
• Suppressor T-cells (TS) slow down activity of B
  and T cells once the antigen has been destroyed
• Memory T-cells cause quicker response if
  infection with same pathogen occurs again

Helper T cell signaling B cell to differentiate
into plasma cell and produce antibodies
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MHC Proteins

• Proteins on the surface of cells that identify a
  cell as belonging to the organism
• Class I MHC are found on all body cells
• Class II MHC are found only on certain cells that
  are part of the immune response
• MHC proteins are used to display foreign antigens
  for recognition by T and B lymphocytes

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Hypersensitivity (allergies)

• When the immune system overresponds to a harmless
  antigen causing tissue damage in the process
• Antigen stimulates overproduction of IgE
  antibodies by B cells (plasma cells)
• IgE antibodies attach to mast cells which contain
  histamine
• Histamine is released in mass quantities when a
  second exposure to the antigen occurs
• Histamine causes the symptoms of allergies

Animation 4
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Active vs. Passive Immunity

• Active - a persons immune system forms memory
  cells against an antigen (either through
  contracting an illness or through a vaccine)
• Passive - a person receives antibodies against an
  antigen but does not form memory cells

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Tissue and Organ Transplants
Each day, about 77 people get the organ
transplant that gives them a second chance, but
19 others die waiting for a donated organ.

• MHC antigens (HLA antigens) are compared to
  determine a match between donor and recipient
• Must be at least 6 MHC antigens in common in
  order to consider a transplant
• Immunosuppressant drugs must be given to prevent
  a rejection

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Inflammation and CV disease

• Some interleukins are released by macrophages and
  endothelial arterial cells
• IL-6 attracts white blood cells to eat
  cholesterol deposited by LDL and burst forming
  plaque