IDF Patient & Family Handbook for Primary Immunodeficiency ... - IDFA

8 The Immune System And Primary Immunodeficiency Diseases
Examples of How the Immune System
Fights Infections
Bacteria
Our bodies are covered with bacteria and our
environment contains bacteria on most surfaces.
Our skin and internal mucous membranes act
as a physical barrier and prevent infection with
those bacteria in most cases. When the skin or
mucous membranes are broken due to disease,
inflammation, or injury, bacteria can enter the
body. An infecting bacteria is usually coated with
complement and antibody once it enters the
tissues and this allows the neutrophil to easily
recognize the bacteria as foreign. The neutrophil
then engulfs the bacteria and destroys it. When
the antibody, complement, and neutrophils are
all functioning normally, this is typically the end
of the process. When the number of bacteria is
overwhelming, or there are defects in antibody,
complement, and/or neutrophils, recurrent
bacterial infections can occur.
Viruses
Most of us are exposed to viruses frequently. The
way our bodies defend against viruses is slightly
different than how we fight bacteria. Viruses
can only survive and multiply inside our cells.
This allows them to hide somewhat from our
immune system. When a virus infects a cell, the
cell releases chemicals to alert other cells to the
infection and prevent other cells from becoming
infected. Many viruses have outsmarted this
protective strategy and they continue to spread
the infection. Circulating T-cells become alerted
to the infection and migrate to the site where they
kill the cells harboring the virus. This is a very
destructive manner to kill the virus since many
of our own cells are sacrificed in the process.
Nevertheless, it is an efficient mechanism to
eradicate the virus. Our bodies have a back-up
strategy so that we do not have to go through the
process of T-lymphocytes killing so many cells
each time we are infected. At the same time, the
T-lymphocytes are killing the virus, they are also
instructing the B-lymphocytes to make antibody.
When we are exposed to the same virus a second
time, the antibody will prevent the infection.