Chapter 43: The Immune System

Disease  A departure from health  Types:  Deficiency diseases  Genetic diseases  Communicable diseases  Contagious disease  Infectious disease  Host provides metabolic needs of pathogen or parasite

Infectious disease

  Transmission     Contact Droplet infection Vector Common vehicle transmission Types     Sporadic disease Endemic disease Epidemic disease Pandemic disease

Adaptations of pathogen to resist host defense

    Cell wall  Contain proteins to resist host &/or antibiotics Sticky capsule  Counters phagocytosis; increases virulence of pathogen Production of enzymes or metabolic toxins Manipulates host cell’s metabolic structure  viruses

Adaptations of the Human Body

  1 st   line of defense Physical shield  Skin, mucus, ciliated cells, tears, urine flow, coughing, sneezing, ear wax Chemical shield   Stomach acids kill bateria Enzymes (lysozyme) in tears etc.  Skin acids 2 nd  line: inflammatory response Increased blood flow  Promotes healing  Swelling insulates tissues

 Macrophages, neutrophils, Eosinophils, & Dendritic cells   Phagocytic activity to engulf pathogen Macrophages:   Develop from monocytes Migrate through the body or reside permanently in some organs (i.e. spleen)    Neutrophils:   Enter infected tissue to engulf microbes Self destruct Eosinophils:  Position against multi-cellular parasite & release enzymes to destroy Dendritic cells:  Can act like macrophages but are usually involved in acquired immunity

  Injured, circulating basophils release histamines & prostaglandins  Promotes vasodilation   Capillaries become “leaky” Attracts phagocytic cells  Neutrophil engulfs bacteria  neutrophil macrophage engulfs Infected cells release interferon  Stimulate adjacent cells to produce proteins that prevent viral replication  Activates phagocytes

3

rd

line: Immune response

 Production of Lymphocytes   Circulate in blood & lymph Concentrated in spleen, lymph nodes, & lymphoid tissue     Each lymphocyte is specific to a particular foreign antigen Originate in stem cells of bone marrow Types:   B cells  Mature in bone marrow T cells  Mature in thymus gland Maturing B cells & T cells tested for self-reactivity & destroyed if self reactive

 Production of specific antibodies by lymphocytes  Antitoxins  Neutralize bacterial toxins   Agglutinins  Clumping of bacteria Opsonins  Stimulate phagocytosis of clumped bacteria   Lysins  Dissolve cell walls of bacteria Precipitins  Coagulation chemicals of bacteria

 Immunoglobins (antibodies)    Specific antigen binding immunoglobulins Generated by B cells Types     IgM  First antibodies to arrive at infection site IgC  Most abundant antibodies in blood & lymph IgA  Antibodies found in body secretions (saliva, sweat) IgE  Trigger release of histamines & other chemicals by mast cells & basophils to cause allergic reactions  IgD   On naïve B cells (not yet exposed to foreign antigen) Receives antigen that leads to clonal selection

 Self/non-self    Immune system must be able to distinguish foreign from non-foreign proteins Major histocompatability complex (MHC)  Group of glycoproteins embedded in cell membrane Two major classes of MHC   Class I MHC  Bind to cytotoxic T cells Class II MHC   Known as antigen presenting cells Bind to specialized cells (macrophages, B cells) & activate T cells

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Action of lymphocytes

Humoral Response     B cells   Enter blood & produce specific antibodies to counter specific antigens Antigen-antibody complexes are formed Helper T cells  Secrete interleukins  Stimulate clonin of B cells to memory cells B cells into memory cells (M cells)    Long lived cells Recognize specific antigen Basis of active immunity Plasma cells (P cells)    Short lived cells Produce additional antibodies with initial exposure to antigen Antibodies draw phagocytic cells in to destroy

 Cell mediated response  Cytotoxic T cells   Stored in thymus gland prior to moving into blood Activated when CD8 receptors recognize antigen on Class I MHC; helper T cell releases cytokines to promote activation      Do not produce antibodies Attack & kill antigen-bearing cells  Secrete proteins that destroy infected cells Stimulate the production of B cells  Dispose of infected cells Suppress B cell reproduction when infection has been suppressed Secrete interferon which defends healthy cells from virus

Primary vs. Secondary immune response

  Primary immune response    First exposure or vaccination to antigen Results in formation a specific antibody to inactivate an antigen Requires time to occur Secondary immune response  Rapid reproduction of specific antibodies to inactivate & destroy antigen (immediate)

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Types of Defense

Innate immunity   Present at birth without any exposure Non-specific Acquired immunity/adaptive immunity    Develops after exposure Highly specific Recognition by lymphocytes

Types of immunity

  Natural immunity  Inherited immunity (parent to child) Active immunity  Long term immunity due to   Exposure (i.e. chicken pox, mumps, measles) Vaccination  Intentional exposure to weakened/dead pathogen or pathogenic toxin  Immunization  Polio...

 Passive immunity    Borrowed or temporary immunity through  Injection of antibodies  Blood serum or gamma globulin injections Immediate immunity Short term immunity  Memory cells are not produced

Blood Groups effect on transfusions & transplants

  Antibodies present against non-self blood types without exposure  result of reaction to bacterial antigens MHC molecules stimulate immune response leading to tissue rejection  each person has a unique polymorphic combination of MHC molecules

Exaggerated, self-directed or diminished immune response & disease

  Allergies    Hypersensitive response to antigens on allergens Often involve IgE antibodies  Attach to mast cells to induce histamine release Anaphylactic shock  Whole body, life threatening allergic reaction Autoimmune disease  Body generates antibodies against self  Ex. Lupus, rheumatoid arthritis, multiple sclerosis, diabetes mellitus

 Immunodeficiency diseases   Inborn or primary  Caused by genetic or developmental defect  Defect in production of immune cells or specific proteins Acquired or secondary  Develops later in life   Caused by exposure to agents or disease Ex. Hodgkin's, AIDS