Specific, non-specific defense and vaccines

The Immune System is the Third Line of Defense Against Infection

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ImmunitySpecific defenses

Immunity

Passive immunityActive immunity

Following clinical infection

Following subclinical infection

Following vaccination Following administration ofImmunoglobulin or antiserum

Transfer of maternal Antibodies Through milk

Transfer of maternal Antibodies Through placenta

natural

acquired

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Active immunity

• Resistance developed in response to stimulus by an antigen.

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Passive immunity

• Immunity conferred by an antibody produced in another host.

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The Immune ResponseImmunity: Ability to recognize and

defend against specific pathogens or antigens.

Immune Response: production of antibodies and specialized lymphocytes

Antigen: Molecules that provoke a specific immune response.

Pathogen – foreign organism

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Innate or Genetic Immunity: Immunity an organism is born with.

Acquired Immunity: Immunity that an organism develops during lifetime.

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Components of Human Immune System

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Types of Acquired ImmunityII. Artificially Acquired Immunity: by vaccine

1. Active – Antigens from vaccines (immunization). – Body makes immune response.– Immunity can be lifelong or temporary

2. Passive: – antibodies (antiserum) introduced by injection.

• Snake antivenom injection from horses or rabbits.– Immunity is short (half life three weeks).– Host immune system does not respond to antigens.

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Antibodies are Produced by B cells Lymphocytes

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Antibodies are Proteins that Recognize Specific Antigens

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Duality of Immune SystemI. Humoral (Antibody-Mediated) Immunity

– antibodies are made to fight antigens.– Antibodies are made by lymphocytes called B cells.– Stimulated B cells will secrete antibodies called

plasma cells.– Antibodies are found in extracellular fluids (blood

plasma, lymph, mucus, etc.) and the surface of B cells.

– Defense against bacteria, bacterial toxins, and viruses that circulate freely in body fluids, before they enter cells.

– Also cause certain reactions against transplanted tissue.

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II. Cell Mediated Immunity– specialized lymphocytes called T cells

• Helper T cells• Cytotoxic T cells

– T cells regulate proliferation and activity cells in the immune system: B cells, macrophage, etc.

– Defense against:• Bacteria and viruses that are inside host cells and are

inaccessible to antibodies.• Fungi• Cancer cells• Transplanted tissue

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Cell Mediated Immunity is Carried Out by T cells

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How Do B Cells Produce Antibodies?– B cells-- develop from stem cells – mature B cells migrate to lymphoid organs

– Clonal Selection: B cell recognizes,

stimulates and divides into plasma cells,

secrete antibodies.– antibodies recognize only one antigen.

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T Cells and Cell Mediated ImmunityAntigens that stimulate this response are mainly

intracellular.

Requires constant presence of antigen to remain effective.

Unlike humoral immunity, cell mediated immunity is not transferred to the fetus.

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T Cells and Cell Mediated ImmunityCellular Components of Immunity:

– T cells have an antigen receptor • recognizes and reacts to a specific antigens

• major histocompatability (MHC) proteins on the surface of cells.

– Clonal selection increases number of T cells.

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T Cells Only Recognize Antigen Associated with MHC Molecules on

Cell Surfaces

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T Cells and Cell Mediated Immunity

Types of T cells1. T Helper (TH) Cells: Central role in immune

response.

• Recognize antigen• Activate macrophages• Induce formation of cytotoxic T cells• Stimulate B cells to produce antibodies.

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Central Role of Helper T Cells

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Types of T cells (Continued)2. Cytotoxic T (Tc) Cells: Destroy target cells.

• Recognize antigens on the surface of all cells:– Kill host cells that are infected with viruses or bacteria.– Recognize and kill cancer cells.– Recognize and destroy transplanted tissue.

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Humoral Response to T Dependent Antigens

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Overview of the Immune Response

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Vaccination

• Vaccination is a method of giving antigen to stimulate the immune response through active immunization.

• A vaccine is an immuno-biological substance designed to produce specific protection against a given disease.

• A vaccine is “antigenic” but not “pathogenic”.

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Periods of maintained immunity due to vaccines• Short period (months): cholera vaccine• Two years: TAB vaccine• Three to five years: DPT vaccine• Five or more years: BCG vaccine• Ten years: yellow fever vaccine• Solid immunity: measles, mumps, and

rubella vaccines.

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Levels of effectiveness

• Absolutely protective(100%): yellow fever vaccine

• Almost absolutely protective (99%): Variola, measles, mumps, rubella vaccines, and diphtheria and tetanus toxoids.

• Highly protective (80-95%): polio, BCG, Hepatitis B, and pertussis vaccines.

• Moderately protective (40-60%) TB, cholera vaccine, and influenza killed vaccine.

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