Taking a Stand : Defense Mechanisms
- Nonspecific defenses are broad based and defend and organism
against many types of pathogens at once
- Species resistance : some diseases are species-specific.
A species will develop diseases that are unique to it and be resistant to
diseases that can attack other species
- Mechanical barriers : skin and mucous membranes
- Enzymatic actions : enzymes naturally present in varies
body fluids will destroy many pathogens. Pepsin in gastric
juices and lysozyme in tears are examples.
- Interferon : a group of proteins that interfere with the
proliferation of viruses
- Inflammation : redness due to vasodilation and subsequent
edema. Pain receptors are stimulated, WBCs accumulate and phagocytosis
occurs. The inflamed area is often enclosed in a fibrin sac to isolate it.
- Phagocytosis : neutrophils and monocytes are attracted
via chemotaxis to inflamed areas
- Specific defenses are otherwise known as immunity
. A specific defense gives resistance to a specific foreign agent. There
are several immune mechanisms. Lymphocytes and macrophages are the main cells
of immunity.
- Lymphocytes originate from several places. T-cells or t-lymphocytes
originate from the thymus. About 70-80% of circulating lymphocytes are t-cells.
B-cells originate from the bone marrow, and are abundant in
the lymph nodes and lymph.
- Before birth, the body takes "inventory" of its proteins. By doing this,
it knows when a foreign substance enters.
- T-cells and B-cells develop receptors on their surfaces allowing them
to recognize and attack invaders, or antigens.
- The "attack" takes different forms. Some attach to an antigen-bearing
cell (bacteria or virus-infected cell) and interact directly – a cell mediated
immunity (CMI) – this is a T-cell type of response, as it is direct. Some
B-cells act indirectly by producing antibodies. This is an antibody mediated
immunity or AMI.
- Activation of the lymphocyte must occur before it can deal with the
antigen. B-cells are activated when an antigen is encounter that fits its
antigen receptors. This makes the B-cells undergo mitosis. Some of the new
B-cells make an antibody, which is similar to the antigen receptor, so it
will attach to the antigen and render it helpless
- Antibodies are made of soluble globular proteins called IgA, IgM, and
IgG. They are all gamma-globulins, and each has specific functions.
- T-cell activation requires an accessory cell. The accessory cell breaks
down the antigen-bearing agent, and then the released antigens are "displayed"
on the accessory cell’s membrane so the T-cell (usually a T-helper cell)
can "examine it."
- An activate T-helper cell that encounters an activated B-cell will release
lymphokines to furthur stimulate the B-cell mitosis
- Cytotoxic T-cells, also called killer T-cells, are activated the same
way B-cells are. Once activated, they release a protein that destroys the
membrane of the pathogenic cell.
- The initial activation of B and/or T-cells by an antigen for the first
time is the primary immune response. After the threat has passed, some of
the B-cells preserve the "memory" of the antigen, so that if it returns,
a secondary immune response can be prompted quickly.
- Immunity
- Naturally acquired active immunity : once exposed to a live pathogen,
the disease is developed and immunity results.
- Vaccine : also called artifically acquired active immunity. Causes a
primary immune response to generate immunity, but does not cause the disease.
- Artificially acquired passive immunity : gamma globulin transfusion
from plasma. A temporary situation at best.
- Naturally acquired passive immunity : transfer of antibodies from mother
to baby.
- Allergies : overreaction to a specific antigen (allergen
)
- Delayed reaction allergy : can occur in anyone. Repeated skin exposure
to certain chemical substances causes, eventually, a T-cell activation, which
then causes a rash
- Immediate reaction allergy : exaggerated reaction. People with this
can synthesize IgE extremely quickly.