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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]