The Immune System

1
The Immune System

• Chapter 43
• Biology Campbell Reece

2
Nonspecific Defenses

• First line of defense
• Unbroken skin (minute cuts will allow the
  bacteria or virus through)
• Mucous membranes (line the digestive, respiratory
  and genitourinary tracts)
• Chemical secretions of skin and mucous membranes
• Lysozyme digests the cell walls of many bacteria

3
Nonspecific Defenses

• Second line of defense
• Phagocytic white blood cells (neutrophils,
  macrophages, eosinophils) ingest the invading
  organism
• Antimicrobial proteins either attack directly
  or inhibit reproduction
• Inflammatory Response blood vessels dilate to
  increase blood flow to the area, histamine is
  released, blood clotting begins, phagocytes are
  sent

4
Inflammatory Response
5
Specific Immunity

• Third line of defense
• Lymphocytes are the key cells of the immune
  system
• B lymphocytes (B cells) develops in the bone
  marrow
• T lymphocytes (T cells) differentiate under the
  influence of the thymus
• Primary immune response attack by the
  lymphocytes the first time the body is exposed

6
Specificity of Lymphocytes

• Antigen a foreign molecule that elicits a
  specific response
• Antibodies proteins that recognize specific
  antigens
• Antigen receptors receptors on the B and T
  cells that bind certain antigens

7
Clonal Selection

• When the antigen is recognized, the proper
  lymphocyte is selected and cloned
• Two forms of clones are produced
• Effector (plasma) cells short-lived cells that
  secrete the specific antibody
• Memory cells long-lived cells bearing receptors
  for the same antigen

8
Clonal Selection
9
Secondary Immune Response

• When the individual is exposed to the same
  antigen later, the response is much faster, of
  greater magnitude, and more prolonged
• The memory cells recognize the antigen and
  produce a response more quickly

10
Distinguishing self from nonself

• The body will destroy any lymphocytes that bear
  receptors for molecules already present in the
  body
• Failure to do this leads to autoimmune diseases
  (such as multiple sclerosis)
• Cells have special glycoproteins on their surface
  called MHC (major histocompatibility complex) or
  HLA (human leukocyte antigens) which mark body
  cells as self

11
Distinguishing self from nonself

• Two types Class I MHC molecules and Class II
  MHC molecules
• Two types of T cells that responds to each kind
  of MHC molecule
• Cytotoxic T cells bind to cells with class I
  MHC molecules
• Helper T cells bind to cells with class II MHC
  molecules
• Triggers an immune response

12
Cytotoxic and Helper T cells
13
Cell-mediated Response

• Class I MHC molecules capture fragments of the
  infecting agent and transport them to the surface
  of the cell
• These foreign particles are presented and a
  cytotoxic T cell is activated
• The cytotoxic T cell kills the infected cell
• The pathogen is now exposed to the antibodies
  that will destroy it

14
Humoral Response

• Initiated when B cells bind with specific
  antigens
• B cells are activated by Interleukin-2 and other
  cytokines secreted from the Helper T cells
• The B cells then generate the plasma cells that
  produce antibodies to destroy the pathogen

15
Antibody Structure Function

• The antigen has several different epitopes or
  locations where an antibody can bind
• A single antigen may bind several antibodies

16
Antibody Structure Function

• Antibodies are also called immunoglobulins
• Each molecule has four polypeptide chains two
  identical heavy chains and two identical light
  chains, joined by disulfide bridges to form a
  Y-shaped molecule
• Variable regions at the ends of the light and
  heavy chains provide the specific binding site

17
Antibody Structure Function
18
Immunoglobulins
19
Antibody-Mediated Disposal of Antigen

• Neutralization the antibody binds to and blocks
  the activity of the antigen
• Opsonization the bound antibodies enhance
  macrophage attachment to the pathogen
• Agglutination clumping of the pathogen
• Complement fixation activation of the
  complement system that leads to cell lysis

20
Antibody-Mediated Disposal of Antigen