Defense Against Infection

The body has three protective barriers from invasion of microorganisms.

1. Natural Resistance - These are mechanical barriers such as intact skin and mucous membranes that keep out microorganisms.

2. Active Immunity (Natural Immunity) - The production of antibodies causing a person to become immune to an antigen. Occurs naturally by exposure to disease.

Active Immunity (Artificial Immunity) - A person forms antibodies to counteract an antigen in the form of a vaccine or a toxoid.

Vaccine - Consists of a low dose of dead or deactivated bacteria or viruses that stimulate the body to produce antibodies against them.

Toxoid - A chemically altered tocsin. The poisonous material produced by a pathogenic organism that triggers the development of antibodies.

Examples - Vaccines for smallpox, polio, tetanus and diphtheria.

3. Passive Immunity (Artificial Immunity) - The administration of the dose of preformed antibodies from the immune serum of an animal, usually a horse.

A. Used when a person is exposed to serious disease, but has no immunity against it.

B. The exposure requires an immediate supply of antibodies to prevent a possible fatal infection (hepatitis, rabies and tetanus).