The Immune System

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The Immune System

• (Chapter 43)

Raj Patel AP Biology 4/27/12
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What Is It?

• The Immune System is designed to help protect the
  human body from outside threats
• These threats include viruses, bacteria, and
  other pathogens
• There are two types of immunity defense Innate
  Immunity and Acquired Immunity.

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Innate Immunity

• Present at start of birth and provides broad
  defense
• Has both external and internal defenses

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External Defenses

• 1) Skin barrier that is hard to penetrate
• 2) Mucous membranes digestive and respiratory
  tract linings that make mucus (traps microbes)
• 3) Secretions saliva, tears, etc. Has lysozymes
  that digest bacterial cell walls.

(1)
(2)
(3)
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Internal Defenses

• 1) Phagocytes
  attach to bacterias
  surface polysaccharide
  receptors
  ? form lysosome vacuoles
  ? engulf
  bacteria

• Types
• Neutrophils enter bacteria site and then engulf,
  but then self-destruct
• Macrophages reside in lymphatic tissue and
  capture bacteria via netlike extensions
• Eosinophils discharge destructive enzymes
• Dendritic cells can also engulf bacteria

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Internal Defenses

• 2) Antimicrobial proteins impede microbe
  reproduction through interferons
• 3) Natural Killer cells kill virus-infected/canc
  er cells by releasing chemicals that cause
  apoptosis (programmed cell death)
• 4) Inflammatory response histamine chemical
  increases blood flow to bacteria site and helps
  clot

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Acquired Immunity

• Main proteins are cytokines, which help activate
  other cells in the immune system (reaction
  pathway)
• Antigen any molecule that elicits a response
  from cytokines
• Epitope portion of antigen that cytokines can
  bind onto in order to recognize molecule

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Acquired Immunity

• 2 Types of lymphocytes
• 1) B lymphocytes (B cells) receptors
  for antigens are Y- shaped and have 4
  polypeptide chains (2 heavy and 2 light).
• 2) T lymphocytes (T cells) receptors for
  antigens have 2 polypeptide chains, a chain and
  ß chain, attached by disulfide bridge
• MHC (major histocompatibility complex) attach to
  antigen and are recognized by T cells.
• ? Class I MHC found on all cells
  bind peptides derived from foreign
  antigens that are synthesized in the cell
• ? Class II MHC bind peptides from foreign
  antigens that are fragmented, or broken,
  from phagocytosis/endocytosis

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Lymphocyte Development

• Lymphocytes arise from stem cells in the bone
  marrow
• B cells develop entirely in bone marrow
• T cells develop in thymus

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Lymphocyte Diversity

• Nearly impossible for two B cells to have same
  exact receptors (same for T cells)
• Each person has 1 million different B cells and
  10 million different T cells
• Differentiation is a result of random gene
  rearrangements in mRNA sequences

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Gene Rearrangements
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Clonal Selection of Lymphocytes

• When an antigen selects a B or T cell, the
  stimulated lymphocyte divides into 2 clone
  daughter cells
• 1st clone is made of many effector cells that
  combat the same antigen (short-lived)
• 2nd clone is made of memory cells that have
  receptors for specific antigens (long-lived)

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Clonal Selection of Lymphocytes

• Clonal Selection antigen driven cloning of
  lymphocytes consists of the steps
• Primary Immune Response peaks after 10-17 days
  after initial exposure to antigen. Plasma cells
  (secrete antibodies) are made.
• Secondary Immune Response peaks after only 2-7
  days after secondary exposure. This response is
  faster, stronger, and longer.

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Humoral/Cell-Mediated Immunity

• Acquired
  
  immunity is
  separated into 2
  
  main branches
  humoral immune
  
  response and
  
  cell-mediated
  
  response.
• Humoral defends
• against pathogens
• toxins.
• Cell-mediated defends
• against infected cells,
• cancer cells, and tissues.

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T Cells

• Helper T Cells when it recognizes an antigen,
  it separates into clones and secrete cytokines
  that stimulate nearby lymphocytes.
• Cytotoxic T Cells uses a surface protein CD8
  that keeps the binding between antigen and T cell
  strong. Used against cancer/infected cells.

LINK
A Overview of the Immune System and Its Cells
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B Cells

• B Cells differentiate into a clone plasma cell
  and a clone memory B cell once stimulated.
• Once finished, the B cell sends the fragmented
  remains of the antigen to a helper T cell to
  finish off.

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Antibody Classes

• There are 5 main types of antibody classes

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Active and Passive Immunity

• Active immunity immunity response that is
  triggered by exposure to an infectious molecule.
• ?Immunization (Vaccination) - develops prior
  to an active immunity response and depends on a
  cells memory of the antigen.
• Passive immunity immunity response that is
  triggered when antibodies from an immune person
  is transferred to someone who is not.

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Blood Groups and Transfusions

• Type A blood cells have the A antigen on the
  surface
• Type B blood cells have the B antigen on the
  surface
• Type AB blood cells have both A and B antigens on
  the surface
• Type O blood cells have neither on the surface

How Do They Work?
Acceptable Transfusions
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Immune Response Side-Effects

• Sometimes, responses from the immune system can
  lead to diseases and conditions that are a result
  of the response.
• Allergies are exaggerated (very sensitive)
  responses to specific antigens called allergens
  that trigger the response.
• In this case, plasma cells secrete antibodies
  usually on pollen grains (hence, spring
  allergies). When the pollen grains enter the
  body again, they induce the cell to release
  histamine and other inflammatory molecules
  (called degranulation).
• As part of the inflammatory response and
  increased blood vessel flow, symptoms like
  sneezing, runny nose, watery eyes, and itchy nose
  can result.

Allergies
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Autoimmune Diseases

• Autoimmune diseases diseases that are triggered
  when immune system loses tolerance against
  itself.
• Antibodies targeted against the bodys own
  natural molecules (histones, DNA breakdown) are
  released and various diseases can result.
• Ex.) Lupus disease characterized by skin
  rashes, fever, arthritis,
  and organ dysfunction.

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Inborn (Primary) Immunodeficiencies

• These deficiencies result from defects in the
  basic development of immune system cells. Both
  innate and acquired defenses can be seriously
  impaired.

Acquired (Secondary) Immunodeficiencies

• These deficiencies can develop later in life and
  are caused by some external agent as opposed to
  natural birth causes.
• Serious developments can impair the immune
  system
• Hodgkins Disease damages the lymphatic system
• AIDS (Acquired Immunodeficiency Syndrome) this
  infamous condition makes infected people severely
  susceptible to immune system breakdowns even
  from the most basic coughs, fevers, colds, etc.