Innate Immunity

The human body has the ability to resist almost all

types of organisms or toxins that tend to damage the

tissues and organs. This capability is called immunity.

Much of immunity is acquired immunity that

does not develop until after the body is first

attacked by a bacterium, virus, or toxin, often

requiring weeks or months to develop the immunity. An additional portion of

immunity results from general processes, rather than from processes directed

at specific disease organisms. This is called innate immunity. It includes the

following:

1. Phagocytosis of bacteria and other invaders by white blood cells and cells

of the tissue macrophage system,

2. Destruction of swallowed organisms by the acid secretions of the stomach

and the digestive enzymes.

3. Resistance of the skin to invasion by organisms.

4. Presence in the blood of certain chemical compounds that attach to

foreign organisms or toxins and destroy them. Some of these compounds

are (1) lysozyme, a mucolytic polysaccharide that attacks bacteria and

causes them to dissolute; (2) basic polypeptides, which react with and

inactivate certain types of gram-positive bacteria; (3) the complement

complex that is described later, a system of about 20 proteins that can be

activated in various ways to destroy bacteria; and (4) natural killer

lymphocytes that can recognize and destroy foreign cells, tumor cells, and

even some infected cells.

This innate immunity makes the human body resistant to such diseases as

some paralytic viral infections of animals, hog cholera, cattle plague, and distemper—

a viral disease that kills a large percentage of dogs that become

afflicted with it. Conversely, many lower animals are resistant or even immune

to many human diseases, such as poliomyelitis, mumps, human cholera, measles,

and syphilis, which are very damaging or even lethal to human beings.