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.

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.

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.