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(pg. 722 – 736)
Guarding against disease

• Specific defenses are those that give us immunity to certain diseases.
• In specific defenses, the immune system forms a chemical “memory” of the invading microbe. If the microbe is encountered again, the body reacts so quickly that few or no symptoms are felt.

• The major players in the immune system include:
• Macrophage (WBC – engulf antigens)
• T cells (helper, cytotoxic, memory) - wbc
• B cells (plasma, memory) - antibodies
• Antibodies

• Antibody: a protein produced by the human immune system to tag and destroy invasive microbes.
• Antibiotic: various chemicals produced by certain soil microbes that are toxic to many bacteria. Some we use as medicines.
• Antigen: any protein that our immune system recognizes as “not self.”

• Antibodies are assembled out of protein chains.
• There are many different chains that the immune system assembles in different ways to make different antibodies.

• Cells of the immune system are “trained” to recognize “self” proteins vs. “not self” proteins.
• If an antigen (“not self”) protein is encountered by a macrophage, it will bring the protein to a helper T-cell for identification.
• If the helper T-cell recognizes the protein as
“not self,” it will launch an immune response.

• Helper T-cells have receptors for recognizing antigens. If they are presented with an antigen, they release cytokines to stimulate B-cell division.
• The helper T-cell is the key cell to signal an immune response. If helper T-cells are disabled, as they are in people with
AIDS, the immune system will not respond.

• B-cells in general produce antibodies. Those with antibodies that bind with the invader’s antigen are stimulated to reproduce rapidly.
• B-cells differentiate into either plasma cells or memory B-cells. Plasma cells rapidly produce antibodies. Memory cells retain the
“memory” of the invader and remain ready to divide rapidly if an invasion occurs again.

• Antibodies released into the blood stream will bind to the antigens for which they are specific.
• Antibodies may disable some microbes, or cause them to stick together
(agglutinate). They “tag” microbes so that the microbes are quickly recognized by various white blood cells.

• While B-cells divide and differentiate, so do T-cells.
• Some Tcells become cytotoxic, or “killer”
T-cells. These T-cells seek out and destroy any antigens in the system, and destroy microbes “tagged” by antibodies.
• Some cytotoxic T-cells can recognize and destroy cancer cells.

• When the invader is destroyed, the helper T-cell calls a halt to the immune response.
• Memory T-cells are formed, which can quickly divide and produce cytotoxic Tcells to quickly fight off the invader if it is encountered again in the future.

• Medical science has created to systems for augmenting the human immune system:
• Antibiotics
• Vaccines

• Antibiotics help destroy bacteria (but not viruses).
• Antibiotics work in one of several ways:
• Slowing bacteria reproduction.
• Interfering with bacterial cell wall formation.

• Antibiotics are not antibodies.
• Antibiotics do not weaken our immune system.
They help it by weakening bacteria.
• Humans do not become “immune” to antibiotics.
Bacteria that resist antibiotics and are not completely destroyed may multiply, producing more antibiotic-resistant bacteria.

• Variolation: The deliberate inoculation of people with secretions from smallpox ( Variola ) sores. Used for centuries in Asia and Africa.
• Vaccination: Invented by Edward Jenner in
1796. Jenner knew that dairy maids who had contracted cowpox never got smallpox. He inoculated a boy with secretions from cowpox sores, and showed the boy was immune to smallpox. (From vacca , Latin for cow.)

• Modern vaccines are created from killed bacteria or viruses, or fragments of proteins from these microbes.
• The proteins are recognized as antigens by our immune systems. This causes a mild immune response. Memory T-cells and B-cells remain ready to fight off the illness if it is encountered again.

• The flu vaccine does not give you the flu. Some people get the vaccine too late, or catch a cold and think they have the flu.
• Vaccines are not less effective than a “natural” infection with the illness. The immunity is the same, and a mild response to a vaccine is much less risky than a full-blown infection of measles.
• Many myths exist about the safety of vaccines.
Vaccine risks are actually very slight.

• Because there are over 100 different known rhinoviruses, it’s possible to catch colds again and again.
• In addition, cold viruses can mutate quickly. No sooner do we have immunity to one form than along comes another.

• Echinacea is supposed to
“strengthen” the immune system.
• Studies in petrie dishes showed Echinacea stimulated white blood cells to produce more virus-killing peroxides, but controlled human trials have found no significant effects.

• Flu viruses also mutate quickly.
• The same form of the flu may have the ability to infect several different vertebrate animals.
• Different forms may hybridize their genetic material, causing new strains to develop in a single generation.

• Allergies are an immune system reaction to harmless antigens.
• Some, such as pollen, may get in through the respiratory system.
Fragments of food proteins may get through the digestive system.
• The next time these proteins are encountered, the immune system attacks them.

• Pollen is a harmless protein, yet we can become allergic to it.
• Most of the symptoms are caused by histamines released by mast cells. That is why antihistamines are used to treat allergies.

• Autoimmune disorders occur when the immune system fails to recognize a protein as “self” and launches an attack.
• Multiple sclerosis, lupus, and rheumatoid arthritis are examples. None of these can be cured, but they can be controlled with drugs.

• Cancer occurs when the mechanisms that control cell division fail, and body cells divide out of control.
• Cytotoxic T-cells can recognize and destroy these cells. But if division is too rapid, the T-cells cannot keep up.
• Some cancer research involves assisting cytotoxic T-cells in recognizing and destroying cancer cells.

• Severe Combined Immune Deficiency is a genetic condition in which one or more genes for proteins crucial for the immune system are defective. Children born with SCID have no immune system.
• Gene therapy has been used to inject a good copy of the defective gene into blood cells or bone marrow cells. In several cases this has been effective, though it is still experimental.

• AIDS (Acquired Immune Deficiency Syndrome) is caused by an infection by the HIV (Human
Immunodeficiency Virus), which attacks and destroys T-helper cells. Because it attacks the immune system directly, finding a vaccine has been difficult.
• Some drugs can slow down HIV reproduction, but no cure exists yet. Prevention is still the best
“cure.”