15.1 Overview of the Innate Defenses (Table 15.1)

1. The innate defense system is composed of first-line defenses, sensor systems such as toll-like receptors and complement, and phagocytes. Inflammation is a coordinated response that involves many aspects of the innate defenses.

15.2 First-Line Defenses (Figures 15.2,15.3)

Physical Barriers

1. The skin provides the most difficult barrier for microbes to penetrate; it is composed of two main layers—the dermis and the epidermis.

2. The cells of the mucous membranes are constantly bathed with mucus and other secretions that help wash microbes from the surfaces. Some mucous membranes have mechanisms that propel microbes, directing them toward areas where they can be eliminated more easily.

Antimicrobial Substances

1. Lysozyme, peroxidase enzymes, lactoferrin, and defensins are antimicrobial substances that inhibit or kill microorganisms.

Normal Flora

1. Members of the normal flora competitively exclude pathogens and stimulate the host defenses.

15.3 The Cells of the Immune System (Figure 15.4, Table 15.2)


1. There are three types of granulocytes—neutrophils, basophils, and eonsinophils.

Mononuclear Phagocytes

1. Monocytes differentiate into either macrophages or dendritic cells. (Figure 15.5)


1. Lymphocytes, which include B cells, T cells, and natural killer (NK) cells, are involved in adaptive immunity.

15.4 Cell Communication

Surface Receptors

1. Surface receptors bind ligands that are on the outside of the cell, enabling the cell to detect that the ligand is present.

Summary 391

2. A macrophage can increase its killing power, becoming an activated macrophage.

3. Macrophages, giant cells, and T-helper cells form concentrated groups called granulomas that wall off and retain organisms or other material that cannot be destroyed by macrophages.

Specialized Attributes of Neutrophils

1. Neutrophils play a critical role during the early stages of inflammation, being the first cell type recruited from the bloodstream to the site of damage.

15.7 Inflammation—A Coordinated Response to Invasion or Damage (Figure 15.10)

1. Swelling, redness, heat, and pain are the signs of inflammation, the attempt by the body to contain a site of damage, localize the response, and restore tissue function.

Factors that Initiate the Inflammatory Response

1. Inflammation is initiated when pro-inflammatory cytokines or other inflammatory mediators are released as a result of the engagement of toll-like receptors or activation of complement by invading microbes, or when tissue damage occurs.

Cytokines (Table 15.3)

1. Cytokines include interleukins (ILs), colony-stimulating factors (CSFs), tumor necrosis factors (TNFs), chemokines, and interferons.

Adhesion Molecules

1. Adhesion molecules allow cells to adhere to other cells.

15.5 Sensor Systems

Toll-Like Receptors (Figure 15.6)

1. Toll-like receptors enable cells to detect molecules that signify the presence of an invading microbe.

The Complement System (Figure 15.7)

1. Complement proteins circulate in the blood and the fluid that bathes tissues; in response to certain stimuli that indicate the presence of foreign material, they become activated.

2. The major protective outcomes of complement activation include opsonization, lysis of foreign cells, and initiation of inflammation.

15.6 Phagocytosis

The Process of Phagocytosis (Figure 15.9)

1. The steps of phagocytosis include chemotaxis, recognition and attachment, engulfment, destruction and digestion, and exocytosis.

Specialized Attributes of Macrophages

1. Macrophages are always present in tissues to some extent, but are able to call in reinforcements when needed.

The Inflammatory Process

1. The inflammatory process leads to a cascade of events that result in dilation of small blood vessels, leakage of fluids from those vessels, and the migration of leukocytes out of the bloodstream and into the tissues.

2. Acute inflammation is marked by a preponderance of neutrophils; chronic inflammation is characterized by the prevalence of macrophages, giant cells, and granulomas.

Outcomes of Inflammation

1. Inflammation can contain an infection, but the process itself can cause damage; a systemic response can be life threatening.

Apoptosis—Controlled Cell Death that Circumvents the Inflammatory Process

1. Apoptosis is a mechanism of eliminating self-cells without evoking an inflammatory response.

15.8 Interferons (Figure 15.11)

1. One of the roles of interferons is to induce cells in the vicinity of a virally infected cell to prepare to cease protein synthesis in the event they become infected with a virus; double-stranded RNA signifies to the cell that it has been infected.

15.9 Fever

1. Fever occurs as a result of certain pro-inflammatory cytokines released by macrophages when their toll-like receptors bind microbial products.

2. Fever inhibits the growth of many pathogens and increases the rate of various body defenses.

392 Chapter 15 The Innate Immune Response

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