Page 25 - Veterinary Immunology, 10th Edition

• Explain why there are two major forms of adaptive immunity: humoral and cell
VetBooks.ir • Understand that adaptive immunity directed against bacterial invaders is
mediated.

mediated by antibodies produced by lymphocytes called B cells.
• Understand that adaptive immunity mediated by lymphocytes called T cells is
called cell-mediated immunity.

• Explain how the adaptive immune system also generates memory cells and the
importance of immunological memory.
• Define innate immunity, adaptive immunity, antibody-mediated immunity and

cell-mediated immunity.

The animal body contains all the components necessary to sustain
life. It is warm, moist, and rich in nutrients. As a result, animal
tissues are extremely attractive to microorganisms that try to invade

the body and exploit these resources for themselves. The magnitude
of this microbial attack can be readily seen when an animal dies.
Within a few hours, especially when warm, a body decomposes
rapidly as bacteria invade its tissues. On the other hand, the tissues

of living, healthy animals are highly resistant to invasion since their
survival depends on preventing microbial invasion. The defense of
the body is encompassed by the discipline of immunology and is
the subject of this book.

Because effective resistance to infection is critical, the body dare
not rely on a single defense mechanism alone. To ensure reliability,
multiple defense systems must be available. Some may be effective
against many different invaders. Others may destroy specific

organisms. Some act at the body surface to exclude invaders. Others
act deep within the body to destroy organisms that have breached
the outer defenses. Some defend against bacterial invaders, some
against viruses that live inside cells, and some against large

invaders such as fungi or parasitic worms and insects. The
protection of the body therefore depends upon a complex system of
overlapping and interlinked defense networks using cells and
molecules that collectively destroy or control almost all invaders.

Any failure in these defenses, permitting invading organisms to
overcome or evade them, will result in disease and possibly death.

25