Chapter Checkpoints
These are some important ideas you are learning in Chapter 14:

Defense Mechanisms of the Host Perspective
The multilevel, interconnecting network of host protection against microbial invasion is organized into three lines of defense. The first line consists of physical and chemical barricades provided by the skin and mucous membranes. The second line encompasses all the nonspecific cells and chemicals found in the tissues and blood. The third line, the specific immune response, is customized to react to specific antigens of a microbial invader. This response immobilizes and destroys the invader every time it appears in the host.

Introducing the Immune System
The immune system operates first as a surveillance system which discriminates between the host's self identity markers and non-self identity markers of foreign cells. When it recognizes that a marker or antigen is foreign, or non-self, the immune system generates a double-pronged response tailored to the specific antigen(s). As far as the immune system is concerned, if an antigen is not self, it is foreign, does not belong, and must be destroyed.

Systems Involved in Immune Defenses
The immune system is a complex collection of fluids and cells that penetrate every organ, tissue space, fluid compartment, and vascular network of the body. The four major subdivisions of this system are the RES, the ECF, the blood vascular system, and the lymphatic system.

The RES, or reticuloendothelial system, is a network of connective tissue fibers inhabited by macrophages ready to attack and ingest microbes invading the first and second lines of defense.

The ECF, or extracellular fluid compartment surrounds all tissue cells and is penetrated by both blood and lymph vessels, which bring all components of the second and third line of defense to attack infectious microbes.

The blood contains both specific and nonspecific defenses. Nonspecific cellular defenses include the granulocytes and macrophages. The two components of the specific immune response are the T lymphocytes, which provide specific cell-mediated immunity and the B lymphocytes, which produce specific antibody or humoral immunity.

The lymphatic system has three functions: 1. It returns tissue fluid to general circulation. 2. It carries away excess fluid in inflamed tissues. 3. Its lymph tissues act as checkpoints for foreign invaders and are the sites which initiate the specific immune response.

Nonspecific Immune Reactions of the Body's Compartments
Nonspecific immune reactions are generalized responses to invasion, regardless of the type. These include inflammation, phagocytosis, interferon, and complement.

The four stages of inflammation are rubor (redness), calor (heat), tumor (edema), and dolor (pain).

Fever is another component of nonspecific immunity. It is caused by both endogenous and exogenous pyrogens. Fever increases the rapidity of the host immune responses and reduces the viability of many microbial invaders.

Macrophages are activated monocytes. Macrophages and neutrophils (PMNS) are the key phagocytic agents of nonspecific response to disease.

The plasma contains complement, a nonspecific group of chemicals that works with the third line of defense to attach foreign cells.

Specific Immunity- The Third and Final Line of Defense
B and T lymphocytes are the agents of the specific immune response. Unlike the nonspecific responses, it develops after exposure to a specific antigen and is tailor-made to it. In addition, the B and T cells ``remember'' the antigen and respond much more rapidly on subsequent exposures.

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