Download The Immune System The immune system is the collection of tissues

The Immune System
The immune system is the collection of tissues, cells, proteins and other molecules that
protect an individual from infection. The immune system is associated with resistance to
viruses and bacteria, but it also includes the host’s ability to resist toxins, transplants and cancer.
We begin to utilize our immune systems as infants when we receive immunizations
[www.geocities.com/Athens/Troy/4383/index01.html]as early as 2 months of age (Table 1)
which are intended to protect us from various pathogens. We continue to receive boosters for
some of these throughout our lives, the best example is the tetanus booster given every 5-10
years.
Most people have become keenly
aware of the importance of the
immune system over the last two
decades because of the spread of the
human immunodeficiency virus (HIV)
which causes
acquired immune deficiency syndrome
[www.niaid.nih.gov/publications/aids.
htm] (AIDS). The depletion of an
infected individual’s immune system
by the virus allows microorganisms
that normally do not grow or cause
problems to flourish and cause
disease. Left uncontrolled those
opportunistic organisms kill.
Table 1
Age
Vaccine
2 months
Diptheria-pertussis-tetanus (DPT),
Poliomyelitis (OPV)
DPT and OPV
OPV
DPT
Varicella zoster (VZV)
Measles-mumps-rubella (MMR)
DPT, OPV, MMR
DPT, MMR, VZV
tetanus
4 months
6-18 months
12-15 months
4-6 years
15 years
After exposure
if not current
There are many genetic diseases, often called primary immunodeficiency diseases,
[www.niaid.nih.gov/Publications/pid/contents.htm] that disrupt the normal function of the
immune system. These accidents of nature have provided insight on how the immune system
functions and remind us about the tenuous environment we really live in. These naturally
occurring defects impact all parts of the immune system including granulocytes, lymphocytes
and soluble substances (e.g. complement components).
Several genetic mutations disrupt the ability of phagocytes to kill bacteria. Collectively, this
disease is called chronic granulomatous disease. Individuals with this disease can live fairly
normal lives. However, they can have episodes where they are confronted with life-threatening
infections by bacteria such as Staphylococcus aureus. Another genetic defect, called leukocyte
adhesion deficiency, affects the ability of white blood cells to leave the blood stream and attack
invading bacteria at sites like skin cuts. These infections can lead to systemic bacterial
infections, septic shock and death. Thus, the phagocytes are critical component to our continued
survival.
People with DiGeorge syndrome lack their thymus and parathyroid glands and are severely
physiologically affected. The thymus is the organ where T-lymphocytes (for “T” for thymus)
develop. The T-lymphocytes mature in the thymus so they can respond to virus-infected cells,
tumors, and transplants. People with DiGeorge syndrome are much like people with acquired
immune deficiency syndrome (AIDS) because they lack T-cells. Moreover, they are highly
susceptible to a number of infections including Pneumocystis carinii, herpes viruses and oral
candidiasis. T-cell deficiencies are severe and people with them rarely survive into adulthood.
The other major lymphocyte subpopulation, the B-lymphocytes are also impacted by a
number of naturally occurring genetic defects. These agammaglobulinemias, can and reduce
selective subpopulations of B cells (e.g. selective IgA deficiency) or can deplete all of the B cells
(congenital agammaglobulinemia).
Pneumococcal and streptococcal bacterial
infections of the lung and upper respiratory tract
are the predominant manifestations of B-cell
deficiencies, but skin and central nervous system
infections also occur with higher frequency.
Life as we know it would not be possible
without our immune systems. This was no better
evidenced than by the life of David Demaret,
“The Bubble Boy”. David was born with
severe combined immune deficiency syndrome
© Baylor College of Medicine
[www.scid.net] (SCIDS). Lacking both B- and
T-lymphocytes, David was forced to live in an 8
x10 plastic enclosure supplied with sterile food,
air and clothes. His only exposure to the outside
similar to that of astronauts on the moon, in a
space suit, specially designed to allow him access
to the world. We take the color of leaves for
granted, but without an immune system, we could
not explore our backyard, let alone the rest of our
galaxy.
As evidenced by AIDS, the immune system can be compromised by the environment.
Viruses, radiation, chemotherapy and stress can depress the immune system. The factors can
make someone more susceptible to infectious disease organisms they might encounter in their
environment, but it can also make them more susceptible to the organisms they normally harbor
and control, the opportunistic pathogens. If we want to explore our galaxy in person, manned
space travel will be necessary. Although our data sets are limited, there is evidence that space
flight can affect a space traveler’s immune status. We know this because delayed-type
hypersensitivity responses which reflect an individuals ability to respond to pathogens to which
they have been vaccinated, are depressed by space shuttle flight! Therefore, understanding the
immune system is a goal of the National Aeronautics and Space Administration [www.nasa.gov]. The
intent of this web-site will be to introduce you to immunology and what we know about the
effects of space travel on the immune system and immune cells.
Bibliography
Kuby, J., Immunology, third edition, W.H. Freeman and Co., NY 1997.
[www.whfreeman.com/immunology]
Sompayrac, L. How the Immune System Works, Blackwell Science, Inc., Malden, MA, 1999.
[www.jleukbio.org]