LESSON 1
IMMUNITY
Section I. INTRODUCTION TO IMMUNITY
1-1.
INTRODUCTION
The concepts of immunology are ancient and pragmatic and are derived primarily
from the study of resistance to infection. Immunity is defined as the physical, chemical,
and cellular defense against antigens and the specific activities of certain body cells
and/or chemical constituents of body fluids that aid in its defense.
1-2.
TYPES OF IMMUNITY
Resistance or immunity to disease can be classified as innate immunity (also
known as natural, native, or inherited) and acquired immunity. If the disease-resisting
ability is a result of one's genetic makeup, and not acquired by exposure to infectious
agents, it is said to be innate immunity. In contrast, acquired immunity develops after
birth and as a result of contact with a foreign substance.
a. Innate Immunity. Innate immunity, known also as natural immunity or
inherited immunity, refers to that type of resistance which each individual has by virtue
of being the individual he or she is in terms of species, race, sex, or other factors
associated with genetically controlled resistance. Natural immunity is commonly
thought of as a nonspecific barrier that is effective against many different kinds of
infectious agents.
b. Acquired Immunity. Acquired immunity is the type of immunity which an
individual develops during a lifetime. It is antigen specific and may be based on
antibodies or may be cell-mediated in origin and more closely associated with the
activities of macrophages and T lymphocytes. This form of immunity is subdivided into
that which is actively acquired and that which is passively acquired. In active immunity,
the individual synthesizes his or her own antibodies; in passive immunity, the individual
receives antibodies from some other individual. Both active and passive immunity are
subdivided into two categories, depending on whether the immunity is acquired by
natural or artificial means.
(1) Active immunity. Active immunity refers to that type of immunity in which
production of significant amounts of antibody occurs about 7 to 14 days (or longer) after
initial exposure to antigen. Upon subsequent exposure, antibody is detectable in 1 to 3
days.
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