Immunity

For a pathogen floating in the air to enter a body and make its host ill, it must pass through multiple lines of defense. The two main types of immunity are innate, or nonspecific immunity, and adaptive, or specific immunity. Innate immunity is the barriers of skin, tears, mucus, and saliva. These, as well as the rapid inflammation of tissues that takes place shortly after injury or infection, physically hinder the entrance of pathogens into the body.

If the pathogen makes it into the body, adaptive, or specific immunity comes into play. There are four important characteristics of adaptive immunity. It:

• 1. Responds only if an invader is present.
• 2. Respondes in a way tailored to act against that specific invader.
• 3. Has a type of "chemical" memory; it reponds more effectively after a first exposure.
• 4. Usually only attacks foreign substances.