Microbiology

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Microbiology Chapter 15

• The Immune system Specific defenses Specific
  immunity
• The immune system is a network of cells and
  organs that extends throughout the
• body and functions as the third line of defense
  against invaders. It is a specific
• response and it generates specific chemicals to
  counteract invaders.
• 1. Foreign substances are antigens
• 2. Proteins made by the body in response are
  called antibodies

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Microbiology Chapter 15

• Two types of immunity
• 1. Active the individual own immune system
  produces the immunity
• A. Naturally acquired by disease
• B. Artificially acquired vaccination
• 2. Passive either have antibodies passed from
  mother to child or having immune globulin
  administered medically

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Microbiology Chapter 15

• Antigens The body can recognize materials as
  non-self or foreign material. These materials are
  called antigens.
• Generally protein or large polysaccharides,
  nucleic acids or lipids are antigenic only if
  combined with protein or polysaccharides
• 2. Any cell, part of a cell, or chemical that
  induces an immune response bythe B-cells or
  T- cells (lymphocytes), is called antigenic.
• 3. Usually large molecules 10,000 mw, in many
  cases the antigen is some particular part of a
  cell like a cell wall polysaccharide, capsule
  material,
• flagella, or fimbriae

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Microbiology Chapter 15

• Antigens The body can recognize materials as
  non-self or foreign material.
• 4. Viral protein, pollen, other protein (egg or
  milk protein) can cause an immune response and
  are antigenic.
• 5. Antibodies tend to react with specific parts
  of an antigen called and antigenic determinant
  or epitope. Size and shape lock-key just like
  in enzyme substrate interactions.
• 6. Small molecules that are too small to cause an
  immune response are called haptens. Penicillin
  is an example. By itself, too small to be
  antigenic, but
• it combines with serum proteins and then can
  become antigenic (penicillin allergy )

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Fig. 15.8
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Microbiology Chapter 15

• Antibodies are produced by Lymphocytes
• 1. T or B cell lymphocytes recognize foreign
  material as antigens.
• 2. They have receptor sites on their cell surface
  that bind antigens in order to eliminate them as
  foreigners.
• 3. The antibody molecules are large proteins that
  are specific in size and shape to interact
  chemically with their particular antigen.
• Antibody structure several kinds of antibodies
  (chart on pg ____)

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Microbiology Chapter 15

• G M A D E
• 1. IgG Monomer, simple antibody, Y shaped,
  composed of two heavy
• chains and two light chains,
• a. The y ends have a variable region, amino
  acid sequence can vary, thus allowing specific
  interaction with their specific antigen they
• have two antigen binding sites
• b. Constant region, on the molecules stem, this
  c region is called
• constant, it can be different (actually have 5
  different c region types
• giving 5 different types of antibodies)
• c. IgG- most prevalent ab, found in blood and it
  is called monomer for
• its simple shape
• d. When acting on antigen, enhances
  phagocytosis, neutralizes toxins
• e. Since it is small, it passes the placenta and
  provides passive
• immunity to infants

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Microbiology Chapter 15

• G M A D E
• 2. IgM Pentamer, composed of 5 monomers (5 Y
  monomer units)
• a. Large and stays in blood stream or attaches
  to blood cells
• b. The first kind of ab to appear after an
  antigenic challenge
• c. Involved in clumping (agglutination)
  reactions, works with complement and clumps
  antigens and cells, so the can be easily
  phagocytized
• d. Kind of reaction seen with ABO blood grouping

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Microbiology Chapter 15

• G M A D E
• 3. IgA Secretory antibody, secreted along
  epithelium linings
• a. Found in respiratory tract, GI tract,
  mothers milk
• b. Localized protection
• 4. IgD function not well known, found on b cell
  surfaces, may function in initiation of immune
  response (B cell activation)
• 5. IgE bound antibodies, found on surfaces of
  mast cells, stimulates inflammatory response,
  may be a trigger for allergic response

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Microbiology Chapter 15

• The immune response B cell immunity (Humoral
  immunity) Know for test
• The B cells are lymphocytes that develop from
  stem cells located in the red bone marrow.
• 1. In embryonic development, stem cells
  differentiate into b cells
• 2. Some move to thymus gland and become T cells
• 3. Both B and T cells later migrate to other
  lymph tissue (lymph nodes, spleen)
• 4. When B cells are exposed to antigens, they
  are activated, they start to divide and become a
  clone of many effector cells called plasma cells

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Microbiology Chapter 15

• The B cells are lymphocytes that develop from
  stem cells located in the red bone marrow.
• 5. The plasma cells produce the antibodies that
  counteract the specific antigen that activated
  the original B cells
• 6. Theory of antibody production Clonal
  selection
• a. During development the B cells undergo
  tremendous genetic
• recombination that results in literally millions
  of different receptor sites on their surfaces.
  These receptor sites are able to bind with the
  specific shape of specific antigens.
• b. Because of the tremendous number of potential
  genetic combinations on the gene regions that
  code for these antigen recognition sites
  millions of possibilities result millions of
  genetically different B cells

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Microbiology Chapter 15

• The B cells are lymphocytes that develop from
  stem cells located in the red bone marrow
• c. Recognition an antigen enters the host, only
  one or a few b cells have a site on its surface
  that fits that antigen (better the fit, the
  betterthe immune response) antigenic
  selection antigen selects its B cell
• d. The specific matching b cell is now activated
  and undergoes cell division into many cells (a
  clone) Clonal selection
• e. See pg ___ -know this for the test be able
  to diagram andexplain

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Microbiology Chapter 15

• i. Recognition
• ii. Activation
• iii. Proliferation
• iv. Differentiation (plasma cells, memory cells)
• v. Production of antibodies (secreted into
  plasma)
• vi. Memory cells long lived cells, survive and
  can respond very quickly if encounter antigen
  again (immunological memory)

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Microbiology Chapter 15

• The first reaction recognition - activation
  proliferation - etc. Takes
• time - This is the primary response 1 to 2
  weeks (pg____)
• Secondary response is very quick memory B cells
  can respond
• quickly to produce more b cells and antibodies,
  just a few days
• How does the body know the difference between
  self and non-self
• material??
• Still a mystery self tolerance, the forbidden
  clone?? Maybe
• the B and T cells that are exposed to self
  antigens are destroyed in fetal development when
  they pass through the thymus gland (clonal
  deletion)

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Microbiology Chapter 15

• T cell response
• T cells T lymphocytes, cell mediated immunity
  just touch on it a little
• 1. T cell activation is different than that of B
  cells
• 2. The antigen that is presented to the T cell is
  first processed by antigen presenting cells
  usually a macrophage
• a. Macrophage encounters antigen ingests it,
  digests it and then seperates it into antgenic
  determinants
• b. Antigenic determinants migrate to the
  phagocyte cell surface
• c. Antigens are held on surface of the phagocyte

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Microbiology Chapter 15

• 3. The correct T cell encounters the antigen on
  the phagocyte and is activated
• 4. T cells then can divide and differentiate into
  different types of T cells
• (be able to list and give a function)
• a. T-helper cells (Th) most prevalent, secrete
  lymphokines
• (interleukins chemical messengers between
  cells of the immune system) see pg ____
• b. Cytotoxic T cells (Tc) destroy target cell
  when in contact
• (virus infected cell killed before virus can
  replicate)
• c. T suppressor cells (Ts) may regulate the
  immune response, turns it off when not needed
• d. Td delayed hypersensitive cells cause
  inflammation
• reaction associated with hypersensitivity, and
  some of the problems with tissue rejection

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Microbiology Chapter 15

• Diagnostic Immunlogy
• Many diagnostic tests in microbiology are based
  on immunology
• 1. Ag Ab reactions can b used to determine
  presence of infection or an exposure to an
  antigen
• 2. Hiv test, Hep C are used to determine exposure
  to these viruses
• 3. Clinical immunology (serology) is the branch
  of immunology involved with identifying cause of
  diseases based on the presence of antigens or
  antibodies in serum of patients
• 4. a good diagnostic immunological test should
  meet two criteria
• a. Specificity test will indicate the presence
  of only one particular antibody or antigen ,
  wont react with even closely related Ag or Ab
• b. Sensitivity can detect even tiny amounts of
  antibodies or antigens in serum

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Microbiology Chapter 15

• c. Titer the serum, with antibodies, is diluted
  and the dilutions are tested for antigens. The
  highest dilution that still tests positive (a
  visible reaction) with the antigen is the titer
• 5. Agglutination test easy to see and read, type
  of test for blood types.
• a. Whole cells are tested for presence of
  antigens on their surfaces
• b. Antiserum is added, if positive (specific ag
  ab reaction), clumping or aggregation of cells
  occurs ( blood typing pg ___)
• c. A,B,O blood groups, rh factor testing ( Photo
  atlas, in lab, page 108-109)
• i. A a ag, antib ab
• ii. B- b ag, anti a ab
• iii. AB both a and b ag and no anti a or b ab
• iv. O neither a or a antigen, both anti a and
  anti b ab

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Microbiology Chapter 15

• 6. Elisa test (EIA test) enzyme linked
  immunosorbent assay (pg 532)
• a. Widely used in clinical labs, adaptable for
  direct assay to detect presence of antigen or
  indirect assay by testing for the presence of
  antibody
• b. These tests can be easily automated and
  results determined by a computer
• Direct ELISA (photo atlas pg 110 111) handout
• 1. Ab for a specific Ag attached to the plastic
  microtiter well
• 2. Test Ag is added, if it binds, then add
  enzme-linked ab
• specific for the test ag
• 3. Then a substrate that is specific for that
  enzyme is added.
• This will produce a specific color change
• 4. The enzyme and substrate are selected so that
  a specific
• color is produced that can be detected in the
  computer
• using optical density reader

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Microbiology Chapter 15

• ii. Indirect like the HIV test.
• Known antigen is attached to the well. Test
  antiserum is added. If it is complementary to
  the
• antigen, it binds. p.532
• Other tests
• Complement fixation test pg 529
• Fluorescent AB pg 530,
• Precipitin,
• Western blot test (confirmatory for HIV after
  ELISA)