The Beginner’s Immune
The immune system, which
is made up of special cells, proteins, tissues, and organs, defends people against germs and microorganisms
The immune system is made up of a network of cells, tissues, and organs that work together to protect the body. The
cells involved are white blood cells, or leukocytes, which come in two basic types that combine to seek out and
destroy disease-causing organisms or substances.
Leukocytes are produced or stored in many locations in the body, including the thymus, spleen, and bone marrow. For
this reason, they're called the lymphoid organs. There are also clumps of lymphoid tissue throughout the body,
primarily as lymph nodes, that house the leukocytes.
The leukocytes circulate through the body between the organs and nodes via lymphatic vessels and blood vessels. In
this way, the immune system works in a coordinated manner to monitor the body for germs or substances that might
The two basic types of leukocytes are:
, cells that chew up invading organisms
, cells that allow the body to remember and recognize previous invaders and help the body destroy
A number of different cells are considered phagocytes. The most common type is the neutrophil, which
primarily fights bacteria. If doctors are worried about a bacterial infection, they might order a blood test to see
if a patient has an increased number of neutrophils triggered by the infection. Other types of phagocytes have
their own jobs 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 start out in the bone
marrow and either stay there and mature into B cells, or they leave for the thymus gland, where they mature into T
cells. B lymphocytes and T lymphocytes have separate functions: B lymphocytes are like the body's military
intelligence system, seeking out their targets and sending defenses to lock onto them. T cells are like the
soldiers, destroying the invaders that the intelligence system has identified.
Here's how it 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 produced, these antibodies continue to exist in a person's body, so that if the same antigen is presented to
the immune system again, the antibodies are already there to do their job. So if someone gets sick with a certain
disease, like chickenpox, that person typically doesn't get sick from it again.
This is also how immunizations prevent certain diseases. An immunization introduces the body to an antigen in a way
that doesn't make someone sick, but does allow 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 antibodies can recognize an antigen and lock onto it, they are not capable of destroying it without help.
That's the job of the T cells, which are part of the system that destroys antigens that have been tagged by
antibodies or cells that have been infected or somehow changed. (Some T cells are actually called "killer cells.")
T cells also are involved in helping signal other cells (like phagocytes) to do their jobs.
Antibodies also can neutralize toxins (poisonous or damaging substances) produced by different organisms. Lastly,
antibodies can activate a group of proteins called complement antibodies that are also part of the immune
system. Complement antibodies assists 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.
The Beginner’s Immune System Primer Top