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Immune System Overview

3 min read

The immune system is the body’s defense against infectious organisms and harmful or toxic compounds. The basic function of the immune system is to attack organisms and substances that invade the body’s systems through a series of steps called the “immune response”.

This system involves a network of cells, tissues and organs that all work together to protect the body. Immune system cells are called “white blood cells” (leukocytes). These come in two basic types that combine to seek out and destroy disease-causing organisms or substances. The two basic types of leukocytes are:

  1. Phagocytes: cells that absorb and destroy invading organisms
  2. Lymphocytes: cells that allow the body to remember and recognize previous invaders and help the body destroy them (creation of antibodies)

A number of different cells are considered phagocytes. The most common type is the neutrophil, which primarily fights bacteria. When looking for evidence of a bacterial infection, a physician may order a blood test to verify an increased number of neutrophils triggered by the infection.

There are several other types of phagocytes, each with their own specific function to make sure that the body responds appropriately to a specific type of invader. The two kinds of lymphocytes are B lymphocytes and T lymphocytes. Lymphocytes are grown in the bone marrow and either mature there into B cells, or migrate to the thymus gland, where they mature into T cells. B lymphocytes and T lymphocytes  have separate functions: B lymphocytes function as the body’s intelligence system, seeking out their targets and sending defenses to lock onto them. T lymphocytes are like soldiers, destroying invaders that the intelligence system has identified.

Here’s how it all works:

When antigens (foreign substances that invade the body) are detected, several types of cells work together to recognize them and respond. These cells trigger the B lymphocytes to produce antibodies, specialized proteins that lock onto specific antigens.

Once antibodies are produced, they continue to exist in a person’s body. These can recognize the same antigen at a later time, and allow the immune system to react quickly. As an example, if someone gets sick with a disease like chickenpox, that person typically doesn’t get sick from it again. The immune system reaction is so fast; the person never experiences the symptoms of the disease. This is also how immunizations may prevent certain diseases.

An immunization (vaccination) introduces a safe or inactive version of an antigen to the body. This allows the body to produce antibodies that will then protect the person from future attack by the germ or substance that produces that particular disease. Although these antibodies have the ability to recognize an antigen and lock onto it, they cannot destroy the invader. T cells are tagged by antibodies or cells that have been infected or somehow changed. These become specialized hunters for the antigens that match their tagged antibodies.

These T cells are called “Killer Cells.” T cells then signal other cells (like phagocytes) to destroy the invader. Antibodies can also neutralize toxins (poisonous or damaging substances) produced by different organisms. Lastly, antibodies can activate the production of complement proteins that assist in killing bacteria, viruses or infected cells.

All of these specialized cells, and parts of the immune system, offer the body protection against disease. This protection is called immunity.