First recorded by the Greek historian Thucydides, who noticed that a person getting a disease and recovering would never catch the same disease again.
This immune response conferred protection against a specific disease.
Discovery of Vaccination
In 1796, Edward Jenner, an English doctor, made the first practical use of Thucydides's observation.
In the 1700s smallpox was one of the deadliest diseases in the world—similar to heart disease and cancer today.
It was commonly known that milkmaids who got cowpox never got smallpox.
Cowpox was a mild disease that caused pox marks on the hands but not much else.
Hypothesis: Jenner suspected that cowpox somehow conferred protection against smallpox.
Experiment: Jenner took the eight-year–old son of his gardener, scratched his arm, and rubbed into it pus from the cowpox blisters on a milkmaid's hands.
The boy became mildly ill with cowpox but recovered quickly.
Six weeks later Jenner exposed the boy to smallpox, and the boy didn't get sick.
Jenner tested him a number of other times, but the boy never became ill with smallpox.
Conclusion: cowpox had provided protection against smallpox.
Jenner named this process vaccination from the Latin word vacca, meaning “cow.”
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Jenner's Dream Accomplished: the Eradication of Smallpox
In 1967, the World Health Organization began a worldwide effort to eradicate smallpox from the planet.
In 1966, 10–15 million people died of smallpox.
By 1978 the disease was eradicated from the face of the earth.
Ironically, the last known death due to smallpox was in England on September 11, 1978.
Currently there are only two known frozen stocks of the virus remaining on Earth:
Centers for Disease Control in Atlanta, Georgia
Vector, the Russian virology institute, in Siberia
The closed circulatory system (heart, arteries, capillaries, veins) contains blood, which is made of two parts:
Blood plasma: water and dissolved solutes
Blood cells: red blood cells, white blood cells, and platelets.
The lymphatic system is a network of lymph capillaries and larger vessels that empty into the circulatory system.
Lymph capillaries end blindly in body tissues.
Space between the circulatory and lymph capillaries is called the interstitial space.
Interstitial: pertaining to being between things, especially between things that are normally closely spaced.
Word derivation:
Inter: between
Sistere: to stand
“To stand between”
Pressure in the blood capillaries is so great that there is a net movement of fluid out of the blood capillaries and into the interstitial space.
This fluid, now known as interstitial fluid, contains white blood cells, water and solutes (red blood cells can't leave the capillaries).
As pressure builds up in the interstitial fluid, the fluid is forced into the lymph capillaries through valve-like openings between the lymph capillaries.
Lymph capillaries flow into larger lymph vessels, which have one way valves (like veins).
Contraction of a variety of muscles through everyday movement squeezes this fluid, now known as lymph, through the system.
It finally enters the circulatory system in a vein near the heart.
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The Main Players
Lymph nodes
The lymph vessels pass through nodes of tissue, about the size of a kidney bean.
These nodes essentially “filter” the lymph.
They are lined with macrophages and lymphocytes, which recognize and destroy pathogens (viruses and bacteria).
The nodes swell during certain diseases as a result of the accumulation of now-dead lymphocytes, macrophages, and infected cells.
Spleen
Similar function as lymph nodes, except that it filters the blood.
Tonsils, adenoids, appendix
Patches of tissue with large numbers of lymphocytes.
Thymus
Located beneath the breastbone (sternum).
Where lymphocytes called T cells mature
Bone marrow
Where all blood cells are made
Where lymphocytes called B cells mature
Figure 18.1, Purves's Life: The Science of Biology, 7th Edition
Antibodies (Immunoglobulins)
Antibodies are key components of the immune system.
Because antibodies are globular proteins and part of the immune system they have a fancy name: immunoglobulins.
They are quaternary proteins composed of two pairs of peptide chains.
One pair: heavy chains
The other pair: light chains
Each peptide chain has a constant region and a variable region.
An immunoglobulin looks like a “Y”: it has two arms and one stem, or base.
The variable regions at the tips of the arms of the antibody form a highly specific binding site for antigens.
An antigen is any molecule that can be considered “foreign.”
The name is short for antibody-generators
Usually a protein or polysaccharide
Examples: toxin (from an insect), the protein coat of a virus, molecules found on the plasma membrane of a bacteria, protists, pollen, transplanted organs, etc.
The part of the antigen that is recognized is called the antigenic determinant.
It matches in a lock-and-key fashion similar to enzymes in their active sites.
Figure 18.10, Purves's Life: The Science of Biology, 7th Edition
Five Classes of Antibodies
Class
General Structure
Location
Function
IgG
Monomer
Free in plasma; about 80 % of circulating antibodies
Most abundant antibody in primary and secondary responses; crosses placenta and provides passive immunization to fetus
IgM
Pentamer
Surface of B cell; free in plasma
Antigen receptor on B cell membrane; first class of antibodies released by B cells during primary response
IgD
Monomer
Surface of B cell
Cell surface receptor of mature B cell; important in B cell activation
IgA
Dimer
Monomer found in plasma; polymers in saliva, tears, milk, and other body secretions
Protects mucosal surfaces; prevents attachment of pathogens to epithelial cells
IgE
Monomer
Secreted by plama cells in skin and tissues lining gastrointestinal and respiratory tracts
Found on mast cells and basophils; when bound to antigens, triggers release of histamine from mast cell or basophil that contributes to inflammation and some allergic responses
Antibodies as Receptors
The stem of the antibody is attached to the plasma membrane of a B cell.
Two arms search the blood and lymph for antigens.
The binding of an antigen to receptor antibodies triggers responses in the cells that bear antibodies.
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Antibodies as Effectors
Effector antibodies circulate in the blood system.
They neutralize poisonous antigens and destroy microbes that bear antigens (the latter is illustrated below).
