Immunology: The Immune System

I. Introduction. (Overhead T20-1)
A. Immunology: the medical study of the immune system, its related structures, associated diseases and conditions, and treatments.
B. Immunity refers to the way in which a healthy body responds to foreign substances.
II. Structure and Function of the Immune System. (Overhead T20-2)
A. The immune system must be able to distinguish foreign substances (nonself) from the body's own tissue (self).
B. Innate (nonspecific) immunity is immunity that is present at birth.
1. Skin and mucous membranes provide physical barriers against foreign substances.
2. Fluids such as gastric juices contain chemicals that kill microorganisms.
3. Leukocytes fight off toxic foreign substances.
C. Adaptive (specific) immunity is acquired during a person’s lifetime.
1. Active adaptive immunity to specific substances is acquired from having had a disease or having had exposure to a disease.
2. Passive adaptive immunity to specific substances is acquired through immunization.
D. An antigen (Ag) is a substance that induces an immune response from the body.
1. It stimulates the body to produce antibodies.
2. Antigens include foreign microscopic organisms such as certain bacteria and viruses.
(a) They also include environmental agents such as pollen, perfume, or food substances when these substances induce an adaptive immune response.
(b) An allergy is an immune response to a specific substance that does not cause an adaptive immune response in most people.
3. Self-antigens are substances produced within the body that induce an immune response.
(a) In beneficial ways they can help the body recognize abnormal cells, such as cancerous cells.
(b) In nonbeneficial ways antigens can destroy normal body tissue. This occurs when the immune system incorrectly identifies body tissue as non-self. Autoimmune diseases are the results of this incorrect identification.
(c) Antigens cause the body to reject transplanted tissue that it does not recognize as self. This is why drugs that suppress the immune system are prescribed for transplant recipients.
III. The Lymphatic System. (Overhead T20-3)
A. The lymphatic system performs a number of functions.
1. It assists in maintaining the body’s fluid balance.
2. It absorbs lipids from the small intestine and transports them to the cardiovascular system.
3. It defends the body against foreign organisms.
B. Lymph is a clear, watery fluid that flows in lymph vessels throughout the body.
C. Interstitial fluid is filtered fluid that becomes lymph once it passes into the lymph capillaries.
D. Lymph nodes are masses of lymphatic tissue contained in capsules of fibrous connective tissue.
1. They produce lymphocytes.
2. They filter lymph.
3. They trap abnormal or foreign substances.
E. The tonsils are located in the pharynx.
1. They provide a ring of lymphatic tissue around the pharynx.
2. They protect the body from harmful substances entering through the mouth and nose.
F. The spleen is located in the upper left quadrant of the abdomen between the diaphragm and stomach.
1. It filters microorganisms, foreign materials, and old erythrocytes from the blood.
2. It stores macrophages, erythrocytes, and platelets.
G. The thymus is located in the mediastinum.
1. It grows until puberty and then shrinks in size.
2. It can produce lymphocytes.
IV. The Immune System at the Cellular Level. (Overhead T20-4)
A. Leukocytes (white blood cells) are a vital component of the immune system.
1. They protect the body from foreign microorganisms.
2. They remove dead cells and debris left behind by the destruction of foreign substances.
3. They are produced in bone marrow and lymphatic tissue.
4. All leukocytes can be divided into two broad categories: granulocytes and agranulocytes.
(a) Neutrophils, basophils, and eosinophils are granulocytes. Granulocytes contain large granules that stain readily, simplifying microscopic identification.
(b) Lymphocytes and monocytes are agranulocytes.
5. There are five types of mature leukocytes.
(a) Neutrophils are first to arrive at the site of an infection.
(1) They surround and swallow up foreign substances by a process called phagocytosis.
(2) They are the most common type of leukocyte.
(b) Monocytes arrive at the site of infection later than neutrophils.
(1) They can ingest a larger quantity of microorganisms than neutrophils.
(2) When they leave the blood and enter the surrounding tissue, they enlarge and become macrophages.
(c) Basophils release histamine and other chemical substances to promote inflammation.
(d) Eosinophils release chemicals that reduce inflammation.
(e) Lymphocytes produce antibodies that contribute to allergic reactions and control tumors.
(1) There are two types of lymphocytes that respond to antigens: B cells and T cells.
(2) B cells are derived from bone marrow.
[a] They are transformed into plasma cells when they encounter an antigen.
[b] They produce an antibody (also called an immunoglobulin) for the specific antigen encountered.
(3) T cells mature and differentiate in the thymus.
[a] Their surfaces contain special receptors that bind with specific antigens, causing an immune response.
[b] Some produce chemicals that destroy microorganisms and control their reproduction.
(4) Natural killer cells (NK) are a type of lymphocyte that can recognize and kill abnormal cells such as tumor cells or virus-infected cells.
B. Major histocompatibility complex (MHC) consists of glycoproteins found in all nucleated cells.
1. Class I is derived from T cells.
2. Class II is derived from B cells.
3. Human leukocyte antigen (HLA) is the most important MHC in humans.
C. Serum complement is a group of more than 34 proteins that circulate in the blood.
1. These proteins facilitate immunological and inflammatory responses.
2. They are usually inactive, but can be activated in a variety of ways.
D. Cytokines are proteins secreted by T cells and monocytes.
1. Interferons protect the body against viral infections.
2. Interleukins stimulate the growth and activities of lymphocytes and mast cells.
3. Tumor necrosis factors (TNF) destroy tumor cells.
4. Colony-stimulating factors (CSF) stimulate the growth of granulocytes and monocytes.
V. Aging of the Immune System. (Overhead T20-5)
A. As an individual ages, the immune system loses its ability to respond to outside antigens and becomes more sensitive to the body’s own antigens.
B. T cells lose their ability to work properly and are no longer able to efficiently destroy abnormal cells.
VI. Examining the Immune System. (Overhead T20-6)
A. Question the patient regarding frequency and type of infections, malaise, unintentional weight loss, and social and family history.
B. Assess risk of HIV infection. At-risk behaviors include intravenous drug use, unsafe sex practices, and a history of other sexually transmitted diseases.
C. Observe for signs of chronic or acute infections and/or irritation(s) indicative of one or more allergies.
D. Look for signs of opportunistic infections such as oropharyngeal candidiasis and lesions on the genitalia or oral mucosa.
E. Order any needed laboratory tests.

VII. Diseases and Conditions. (Overhead T20-7)
A. Acquired immunodeficiency syndrome (AIDS): a life-threatening immunodeficiency disease caused by the human immunodeficiency virus (HIV).
B. Allergic rhinitis: an antigen-antibody reaction that results in inflammation of the mucous membranes and is typically accompanied by sneezing, coughing, etc.
C. Contact dermatitis: inflammation of the skin and mucous membranes arising from hypersensitivity to environmental allergens.
D. Hay fever: acute seasonal allergic rhinitis typically caused by reactions to wind-borne allergens such as ragweed and flower pollens.
E. Hodgkin disease: a proliferation of malignant growths within the lymphatic system.
F. Hypersensitivity disorder: a harmful response to an antigen that does not cause an adaptive immune response in most people. Also called an allergy.
G. Lymphoma: a neoplasm of the lymphatic tissue that is usually malignant.
H. Mononucleosis: a condition caused by the Epstein-Barr virus that is characterized by fever, pharyngitis, etc.

VIII. Common Diagnostic Tests and Procedures. (Overhead T20-8)
A. Agglutination tests: a group of tests in which blood serum is tested for the presence of specific antibodies.
B. Bacterial culture: Samples of purulent tissue are sent to the laboratory and cultured to determine whether bacteria are present and, if so, their type(s).
C. Complement deficiency tests: blood is checked for complement deficiency that may indicate an immunodeficiency disorder.
D. ELISA: a group of blood tests used as a preliminary screening tool to detect the presence of a specific antigen or antibody in blood serum.
E. Lymphangiography: radioactive material is injected into the lymph vessels and x-rays are taken. Useful in diagnosing lymphoma.
F. Patch test: a small piece of gauze or filter paper saturated with a test substance is placed on the skin to determine whether there is an allergic reaction. The test is positive if a reaction occurs.
G. RAST test (radioallergosorbent test): blood serum is tested for the amount of specific antibodies (IgE) present, aiding in identifying patient allergen(s).
H. Western blot (WB): blood serum is tested for the presence of antibodies to specific antigens.
IX. Drug Classifications. (Overhead T20-9)
A. AIDS drug: prevention of the progression of HIV infection and treatment of the symptoms associated with AIDS.
B. Antihistamine: reduction of the inflammation, itching, and swelling caused by allergic reactions.
C. Immunostimulant/immunomodulator: stimulation of immune system activity in the treatment of conditions such as chronic hepatitis C and multiple sclerosis.
D. Immunosuppressant: suppression of immune activity, thereby preventing rejection of organ transplants. Also used in the treatment of autoimmune disorders.
E. Mast cell inhibitor: prevention of the release of histamine by mast cells.
F. Vaccine: stimulation of an immune response against a pathogen to prevent infection or reaction.

X. Therapeutic Procedures. (Overhead T20-10)
A. Splenectomy: surgical removal of the spleen.
B. Thymectomy: surgical removal of the thymus.
C. Transplantation of thymic tissue from stillborn infants into children whose lymphatic system is abnormal in hopes of restoring the immune system to normal.
- posted by gopi @ 6:36 AM