Adaptive Body Defense (Third line of defense)

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14 Terms

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The Final Line of Defense
Adaptive or Specific Immunity

  • Features of Adaptive Immunity:

    • Antigen specificity - selectively recognizes and acts against particular foreign substances (i.e. immunity to one disease does not necessarily cause immunity to another).

    • Acquired - because it develops during a person’s lifetime on exposure to specific harmful agents.

    • Systemic - not restricted to the initial infection site.

    • Memory - recognizes and mounts a stronger attack on previously encountered pathogens.

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Adaptive Body Defenses

  • Immune response - is the Immune system’s response to a threat such as microorganisms, pollen, drugs, poison ivy, animal dander, detergents etc.(most of them are proteins)

  • Initial exposure - primes the body

  • Antigens - are molecules which elicit an immune response or bind to components of the immune system, such as antibodies.

  • Self-antigens:

    • Human cells have many surface proteins.

    • Our immune cells do not attack our own proteins.

    • MHC-Major histocompatibility Complex (serves as a barcode)

    • In an Autoimmune disease, body fights against its own cells.

  • Haptens - are small molecules which are antigenic in nature, but cannot elicit an immune response; this means that a hapten can only react with a specific antibody but cannot trigger an immune response. Hapten is essentially an incomplete antigen.

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Cells of the Adaptive Defense system

Lymphocytes:

  • •Both T and B lymphocytes develop from hemocytoblasts (stem cells) in the red bone marrow, as do all blood cells.

  • T Lymphocytes-  migrate to thymus and become T cells (this constitutes about 80% of lymphocytes in blood).They undergo maturation in the Thymus directed by the hormone Thymosin.

  • B Lymphocytes- develop immunocompetence in the bone marrow itself.

  • Antigen Presenting Cells (APCs): mediate the cellular immune response by processing and presenting antigens for recognition by certain lymphocytes such as T cells.

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APCs

Dendritic cells

Macrophage

B Lymphocytes

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Adaptive Immunity - Classification

  • There are two major types of Adaptive Immunity:

    • Humoral Immunity – “B” Cell mediated

  • Cell Mediated Immunity – “T” cell mediated

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Adaptive Defense
Humoral Immunity - B Cell mediated

  • The B lymphocytes (B cells) mature in the red bone marrow before becoming active in the blood.

  • B cells have surface receptors that bind with a specific type of antigen.

  • This binding sensitizes, the lymphocytes to Clonal Selection.

  • B cells rapidly multiply into large numbers of plasma cells.

  • The plasma cells produce antibodies or immunoglobulins (Igs) against the original antigen, and release them into the blood, providing a form of immunity described as humoral immunity.

  • Primary Response - 4-5 days; Antibody peak in 10 days.

  • Those B cells that do not become plasma cells become the Memory cells for future attack by the same antigen.

  • Secondary Response – within hours; antibody peaks in 2-3 days.

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Adaptive Immunity:
Antibodies / Immunoglobulins

  • All antibodies are contained in a portion of the blood plasma called gamma globulin fraction.

  • The antibody can bind only to the antigen that caused its production.

  • Antibodies do not destroy cells directly; rather, they assist in the immune response.

  • Some of the activated B cells do not become plasma cells but, like certain T cells, become memory cells.

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Classes of Antibodies

There are five different classes of antibodies (“GAMED”)

  • IgG (75%)—found in blood, lymph, and intestines, can cross the placental barrier and confer immunity from mother to fetus;

  • IgA (15%)—found mainly in exocrine gland secretions, nasal fluid, tears, gastric and intestinal juice, bile, breast milk and urine

  • IgM (5%-10%)—found in blood and lymph; first antibody produced in an immune response.

  • IgE (<0.1%)—located on basophils and mast cells- active in allergic reactions and parasitic infections.

  • IgD (< 1%)—located on surface of B cells.

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Functions of the Antibodies

  • Complement fixation – there are 20 inactive complements that get activated

  • Neutralization – when they bind to specific sites and block the harmful effects of the virus / exotoxin.

  • Agglutination – process causing clumping of the foreign cells.

  • Precipitation – as a result of the cross linking process the antigens become large, insoluble and settle out as precipitates.

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Naturally Acquired Immunity

  • Naturally Acquired Active Immunity:

    • Occurs naturally through contact with a specific pathogen or its toxins.

      • Ex: suffering the disease like Measles.

    • May last for years, and in some cases for life.

    • Because the host is actively involved in generating protection, this type is described as active immunity.

    • Because the immunity is formed against harmful agents encountered in the normal course of life, it is called natural active immunity.

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Natural Passive Immunity

  • Naturally Acquired Passive Immunity:

    • Occurs when antibodies are obtained from someone else.

      • Conferred naturally from a mother to her fetus (naturally acquired) through placenta.

      • Conferred naturally from receiving gamma globulin, via breast milk.

    • These donated antibodies provide immediate protection, but only lasts 2-3 weeks.

    • Immunological memory does not occur.

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Artificially Acquired Immunity

  • A person unexposed to a particular antigen has no antibodies or T cells against that pathogen, and may be defenseless against that infection.

  • Hence artificial measures may be used to establish immunity.

  • Artificially acquired immunity may be

    • Artificially Aquired Active Immunity:

    Vaccination: Artificial acquired active immunity is

     through vaccinations against particular pathogens.

  • Artificially Aquired Passive Immunity:

    Immune Sera: Artificial acquired passive immunity is

    through injection of immune globulins (gamma globulins)

    after presumed exposure to a particular pathogen.

         Ex: Anti Tetanus Serum

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Adaptive Immunity:
Cell Mediated Immunity - T cell Mediated

  • There are several types of T cells, each with different function:

    • Helper T cells:

      • Release substances such as Cytokines.

      • Cytokines stimulate the production of more cytotoxic T cells, B cells and macrophages.

      • Note: The Corona Virus is causing a Cytokine storm to hit the body’s immune system.

    • Cytotoxic or Killer T cells: (Phagocytosis)

      • Recognize cells infected with viruses or other intracellular pathogens, cancer cells, and foreign antigens present on transplanted tissue.

      • Binding to a foreign cell, releases toxins called Perforins which form pores in the plasma membrane of these cells, allowing Granzymes to enter and destroy them.

  • Suppressor T cells:

    • Halts the immune response in order to prevent over-activity of the T and B cells.

  • Memory T cells:

     Left behind in the system to remember the antigen and start

     a rapid response if that antigen is encountered again.

  • These thymus-derived lymphocytes produce an immunity that is called the cell-mediated immunity.

  • The T cell population is generally responsible for defense against  -

    • cancer cells

    • certain intracellular viruses

    • the rejection of tissues transplanted from another person.

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Disorders of Immunity

Autoimmune Diseases:
  Body reacts to its own tissues.
- Rheumatoid Arthritis
- Myasthenia Gravis
- Multiple Sclerosis
- Grave’s Disease
- Type I Diabetes Mellitus
- Systemic Lupus Erythematosus
- Glomerulonephritis

Allergies and Anaphylaxis:
  (Anaphylaxis – is the life threatening form of severe allergy)

*AIDS: opportunistic infections