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Inflammatory Response

What happens when an enemy gets past the first line of defense?

For this running back to make it past the first line of defense, there usually has to be a hole or break in the line. He then runs into the secondary, or the second line of defense. Whenever the skin is broken, it is possible for pathogens to easily enter your body. They get past the first line of defense, and run into the second line of defense.

The Second Line of Defense

If you have a cut on your hand, the break in the skin provides a way for pathogens to enter your body. Assume bacteria enter through the cut and infect the wound. These bacteria would then encounter the body’s second line of defense.

Inflammatory Response

The cut on your hand may become red, warm, and swollen. These are signs of an inflammatory response. This is the first reaction of the body to tissue damage or infection. As explained in the figure below, the response is triggered by chemicals called cytokines and histamines, which are released when tissue is injured or infected. The chemicals communicate with other cells and coordinate the inflammatory response. You can see an animation of the inflammatory response at this link.

Elements of an inflammatory response

This drawing shows what happens during the inflammatory response. Why are changes in capillaries important for this response?


The chemicals that trigger an inflammatory response attract leukocytes to the site of injury or infection. Leukocytes are white blood cells. Their role is to fight infections and get rid of debris. Leukocytes may respond with either a nonspecific or a specific defense.

  • A nonspecific defense is the same no matter what type of pathogen is involved. An example of a nonspecific defense is phagocytosis. This is the process in which leukocytes engulf and break down pathogens and debris. It is illustrated in the figure below. The immune system’s first line of defense is also a nonspecific defense.
  • A specific defense is tailored to a particular pathogen. Leukocytes involved in this type of defense are part of the immune response and are described in other concepts.
Leukocytes attacking pathogens

In this image, leukocytes (white) are attacking pathogens (star-shaped).


  • The second line of defense attacks pathogens that manage to enter the body.
  • The second line of defense includes the inflammatory response and phagocytosis by nonspecific leukocytes.

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