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CHAPTER

3

Immunity, Infection,

& Inflammation

OBJECTIVES

After studying this chapter, you should be able to:

■

Understand the significance of immunity, particularly with respect to defending

the body against microbial invaders.

■

Define the circulating and tissue cell types that contribute to immune and inflam-

matory responses.

■

Describe how phagocytes are able to kill internalized bacteria.

■

Identify the functions of hematopoietic growth factors, cytokines, and chemokines.

■

Delineate the roles and mechanisms of innate, acquired, humoral, and cellular im-

munity.

■

Understand the basis of inflammatory responses and wound healing.

INTRODUCTION

As an open system, the body is continuously called upon to

defend itself from potentially harmful invaders such as bacte-

ria, viruses, and other microbes. This is accomplished by the

immune system, which is subdivided into innate and adaptive

(or acquired) branches. The immune system is composed of

specialized effector cells that sense and respond to foreign

antigens and other molecular patterns not found in human

tissues. Likewise, the immune system clears the body’s own

cells that have become senescent or abnormal, such as cancer

cells. Finally, occasionally, normal host tissues become the

subject of inappropriate immune attack, such as in autoim-

mune diseases or in settings where normal cells are harmed as

innocent bystanders when the immune system mounts an

inflammatory response to an invader. It is beyond the scope of

this volume to provide a full treatment of all aspects of mod-

ern immunology. Nevertheless, the student of physiology

should have a working knowledge of immune functions and

their regulation, due to a growing appreciation for the ways in

which the immune system can contribute to normal physio-

logical regulation in a variety of tissues, as well as contribu-

tions of immune effectors to pathophysiology.

IMMUNE EFFECTOR CELLS

Many immune effector cells circulate in the blood as the white
blood cells. In addition, the blood is the conduit for the pre-
cursor cells that eventually develop into the immune cells of
the tissues. The circulating immunologic cells include
granu-
locytes (polymorphonuclear leukocytes, PMNs),
comprising
neutrophils, eosinophils,
and
basophils; lymphocytes;
and

monocytes.

Immune responses in the tissues are further am-

plified by these cells following their extravascular migration,

as well as tissue

macrophages

(derived from monocytes) and

mast cells

(related to basophils). Acting together, these cells

provide the body with powerful defenses against tumors and

viral, bacterial, and parasitic infections.