Animal Defense Systems

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Animal Defense Systems

• Animal defense systems are based on the
  distinction between self and nonself.
• There are two general types of defense
  mechanisms
• Nonspecific defenses, or innate defenses, are
  inherited mechanisms that protect the body from
  many different pathogens.
• Specific defenses are adaptive mechanisms that
  protect against specific targets.

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Animal Defense Systems

• White blood cells are important in defense.
• All blood cells originate from stem cells in the
  bone marrow.
• White blood cells (leukocytes) are clear and have
  a nucleus and organelles.
• White blood cells can leave the circulatory
  system.
• The number of white blood cells sometimes rises
  in response to invading pathogens.

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Animal Defense Systems

• There are two main groups of white blood cells
  phagocytes and lymphocytes.
• Phagocytes engulf and digest foreign materials.
• Lymphocytes are most abundant. There are two
  types B and T cells.
• T cells migrate from the circulation to the
  thymus, where they mature.
• B cells circulate and also collect in lymph
  vessels, and make antibodies.

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Animal Defense Systems

• Four groups of proteins play key roles in
  defending against disease
• Antibodies, secreted by B cells, bind
  specifically to certain substances.
• T cell receptors are cell surface receptors that
  bind nonself substances on the surface of other
  cells.
• Major histocompatibility complex (MHC) proteins
  are exposed outside cells of mammals. These
  proteins help to distinguish self from nonself.
• Cytokines are soluble signal proteins released by
  T cells. They bind and alter the behavior of
  their target cells.

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Nonspecific Defenses

• Vertebrate blood contains about 20 antimicrobial
  complement proteins.
• Complement proteins provide three types of
  defenses
• They attach to microbes, helping phagocytes
  recognize and destroy them.
• They activate the inflammation response and
  attract phagocytes to the site of infection.
• They kill invading cells.

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Nonspecific Defenses

• Phagocytes ingest pathogens. There are several
  types of phagocytes
• Neutrophils attack pathogens in infected tissue.
• Monocytes mature into macrophages. They live
  longer and consume larger numbers of pathogens
  than do neutrophils. Some roam and others are
  stationary in lymph nodes and lymphoid tissue.
• Eosinophils kill parasites, such as worms, that
  have been coated with antibodies.
• Dendritic cells have highly folded plasma
  membranes that can capture invading pathogens.

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Nonspecific Defenses

• Natural killer cells are a class of nonphagocytic
  white blood cells
• They can initiate the lysis of virus-infected
  cells and some tumor cells.

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Nonspecific Defenses

• The inflammation response is used in dealing with
  infection or tissue damage.
• Mast cells and white blood cells called basophils
  release histamine, which triggers inflammation.

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Specific Defenses The Immune System

• Four characteristics of the immune system
• 1. Specificity Antigens are organisms or
  molecules that are specifically recognized by T
  cell receptors and antibodies.
• The sites on antigens that the immune system
  recognizes are the antigenic determinants (or
  epitopes).
• Each antigen typically has several different
  antigenic determinants.
• The host creates T cells and/or antibodies that
  are specific to the antigenic determinants.

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Specific Defenses The Immune System

• 2. Diversity
• It is estimated that the human immune system can
  distinguish and respond to 10 million different
  antigenic determinants.
• 3. Distinguishing self from nonself
• Each normal cell in the body bears a tremendous
  number of antigenic determinants. It is crucial
  that the immune system leave these alone.
• 4. Immunological memory
• Once exposed to a pathogen, the immune system
  remembers it and mounts future responses much
  more rapidly.

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Specific Defenses The Immune System

• The immune system has two responses against
  invaders The humoral immune response and the
  cellular immune response.
• The two responses operate in concert and share
  mechanisms.

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Specific Defenses The Immune System

• The humoral immune response involves antibodies
  that recognize antigenic determinants by shape
  and composition.
• The cellular immune response is able to detect
  antigens that reside within cells.
• It destroys virus-infected or mutated cells.
• Its main component consists of T cells.
• T cells have T cell receptors that can recognize
  and bind specific antigenic determinants.

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Specific Defenses The Immune System

• When the body encounters an antigen for the first
  time, a primary immune response is activated.
• When the antigen appears again, a secondary
  immune response occurs. This response is much
  more rapid, because of immunological memory.

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Specific Defenses The Immune System

• Artificial immunity is acquired by the
  introduction of antigenic determinants into the
  body.
• Vaccination is inoculation with whole pathogens
  that have been modified so they cannot cause
  disease.
• Immunization is inoculation with antigenic
  proteins, pathogen fragments, or other molecular
  antigens.
• Immunization and vaccination initiate a primary
  immune response that generates memory cells
  without making the person ill.

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B Cells The Humoral Immune Response

• Antibody molecules are proteins called
  immunoglobulins.
• Five Classes/Types of IG's.
• G,M,D,A and E

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Figure 18.10 Structure of Immunoglobulins (Part
1)
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Figure 18.11 IgG Antibodies Promote Phagocytosis
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T Cells The Cellular Immune Response

• T cells, like B cells, possess specific surface
  receptors.
• The genes that code for T cell receptors are
  similar to those for immunoglobulins.
• T cell receptors also have constant and variable
  regions.
• A major difference between antibodies and T cell
  receptors is that T cell receptors bind only to
  an antigenic determinant that is displayed on the
  surface of an antigen-presenting cell.

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T Cells The Cellular Immune Response

• Activated T cells give rise to two types of
  effector cells.
• Cytotoxic cells, or TC, recognize virus-infected
  cells and kill them by causing them to lyse.
• Helper T cells, or TH cells, assist both the
  cellular and humoral immune systems.
• Activated helper T cells proliferate and
  stimulate both B and TC cells to divide.
• HIV

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Figure 18.16 The Interaction between T Cells and
Antigen-Presenting Cells (Part 3)
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Figure 18.15 Macrophages Are Antigen-Presenting
Cells
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Figure 18.17 (a) Phases of the Humoral and
Cellular Immune Responses (Part 1)
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Figure 18.17 (a) Phases of the Humoral and
Cellular Immune Responses (Part 2)
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Figure 18.17 (b) Phases of the Humoral and
Cellular Immune Responses (Part 1)
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Figure 18.17 (b) Phases of the Humoral and
Cellular Immune Responses (Part 2)
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T Cells The Cellular Immune Response

• T cells developing in the thymus are tested to
  ensure that they will be functional and will not
  attack normal self antigens.
• If the developing T cell binds to one of the
  bodys own normal antigens, it undergoes
  apoptosis.

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T Cells The Cellular Immune Response

• For organ transplants to be successful, MHC
  molecules must match otherwise, these same
  molecules will act as antigens.
• The cellular immune system is responsible for
  rejection.
• Rejection problems can be controlled somewhat by
  treating patients with immunosuppressing drugs.

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Disorders of the Immune System

• The human immune system can overreact to a dose
  of antigen and produce an inappropriate immune
  response. Allergies are the most familiar
  example.
• Immediate hypersensitivity.
• Delayed hypersensitivity.