Immunity

 q       Immune defends the body against infection, toxins.

q       Many layers of defense.

o        First Line

§         Skin

·         Is a tight barrier preventing access of antigens

§         Mucous membrane

·         Secretes mucous which adheres / binds antigens

§         Mucous Secretions

·         Often contain lysozymes which lyse bacteria

o        Second Line

§         Phagocytic WBC’s

·         Non-specific immunity where phagocytic WBCs attack and ingest invading organisms

·         These include

o        Neutrophils (60-70% of WBCs)

o        Monocytes / Macrophages (5%)

o        Eosonophils

§         Attack larger antigens by secreting enzymes

o        Natural Killer (NK) cells

§         Specialize in destroying virus infected, worn, or defective cells by lysing them

 

Types of WBCs

 

§         Inflammatory Response

·         Response to damage of tissue

·         Many step process

o        Chemical signals of injury are released by damaged cells.  These include histamines & prostaglandins

o        Signals increase permeability of local capillaries allowing the passage of phagocytes and clotting components to the injured area

o        Phagocytes consume any invading pathogens and foreign materials which may have entered the wound

 

§         Antimicrobial Proteins

·         Include interferons which are released by virus-infected cells.

·         Inhibit infection of neighboring cells

 

Specific Immunity

q       Mediated by WBCs  called lymphocytes.

o        Respond to Specific antigens hence the term specific immunity.

o        Any molecule which elicits this immune response is termed an antigen

o        Antigens often stimulate B-cell lymphocytes to secrete antibodies.

o        Antibodies are molecules designed and manufactured to interfere with certain molecules/antigens

 

q       Works according to following process

o        Antigen binds to antigen receptors of the lymphocyte cells

o        Once stimulated the stem cells divide into either effector or memory cells

§         Effector cells (often called plasma cells) are short lived cells which secrete antibodies to the specific antigen

§         Memory cells are long lived cells bearing antigen specific receptor sites

 

 

§         Memory cells allow a more rapid and effective defense against an antigen the next time it is encountered.

 

o        Cells have the ability to recognize self from non self through surface markers

 

Antibody production

q       Primary response – results from the 1^st exposure of a B cell to an antigen for which it is specific, and produces specific antibodies usually IgM and IgD.  Normally takes 3 to 14 days to produce enough antibodies  to be effective against the antigen

q        Secondary response (memory) – immune system is exposed to an antigen it has already produced antibodies to.  Provides better protection than primary.  Time to produce antibodies is hours to a few days.  The amount of antibody produced is much larger.

Helper T Cells

o        Macrophages Can present antigens to Helper T cells after ingesting an antigen

o        Helper T cells can then stimulate either B Cells or Cytotoxic cells to mount a defense.

§         Cytotoxic lymphocytes work by lysing target cells through secretion of enzymes.  Usually perforin

 

Overview of immune responses

 

Antibodies

 

 

q       Composed solely of proteins

q       Designed to attach to specific antigens @ specific binding sites

q       Composed of a Constant region (Does Not Change), and 2 or more variable regions which bind to an antigen

 

 

q       Have several shapes but generally the same function

 

 

q       Work through the following mechanisms:

o        Neutralize viruses by preventing binding to cells

 

o        Forcing agglutination of particles, thus neutralizing them

 

o        Forcing precipitation of soluble antigens

o        Enhancing phagocytosis by marking targets for WBCs

 

Types of Acquired Immunity:

 

1.     Active Natural Immunity – natural exposure to an antigen.

2.     Active Artificial Immunity – antigen is deliberately introduced to stimulate the immune system.  This process is vaccination, and the introduced antigen is the vaccine.  The vaccine is either part of the microbe, dead microorganisms, or an altered microorganism.

3.     Passive Natural Immunity – transfer of antibodies from a mother to child across the placenta before birth.  IgG provides protection for the first few months.  IgA can also be passed to the newborn through colostrums and milk.

4.     Passive Artificial Immunity – vaccinating an animal, antibodies and T cells are removed from animal and injected into the individual requiring immunity.  Temporary immunity.  Antiserum serum that contains antibodies responsible for passive artificial immunity.  Rabies, hepatitis, measles, bacterial toxins such as tetanus, diphtheria, botulism, and venoms from poisonous snakes and spiders.