Biology & Life Sciences Chapter 18 Homework Hypersensitivity And Autoimmune Disease Commences When

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CHAPTER

Immune Disorders

Chapter Outline

Hypersensitivities (pp. 522–534)

Type I (Immediate) Hypersensitivity

Type II (Cytotoxic) Hypersensitivity

Type III (Immune Complex–Mediated) Hypersensitivity

Type IV (Delayed or Cell-Mediated) Hypersensitivity

Autoimmune Diseases (pp. 534–536)

Causes of Autoimmune Diseases

Examples of Autoimmune Diseases

Immunodeficiency Diseases (pp. 536–544)

Chapter Summary

Hypersensitivities (pp. 522–534)

If the immune system functions excessively, the body develops any of a variety of immune hy-

persensitivities, such as allergies. Hypersensitivities may be more precisely defined as any im-

mune response against a foreign antigen that is exaggerated beyond the norm. For example,

itching in response to contact with wool is an example of a hypersensitivity response.

Type I (Immediate) Hypersensitivity

Type I hypersensitivities are localized or systemic (whole body) reactions that result from the

release of inflammatory molecules such as histamine. These responses are termed immediate

Sensitization upon Initial Exposure to an Allergen

In some individuals, B cells are stimulated to become plasma cells producing IgE against aller-

Instructor’s Manual for Microbiology with Diseases by Body System, 5e

Degranulation of Sensitized Cells

When the same allergen enters the body again, it binds to the active sites of IgE molecules on

The Roles of Degranulating Cells in an Allergic Reaction

Mast cells are large cells distributed throughout the body in connective tissues other than blood.

Their cytoplasm is full of granules of inflammatory chemicals. One significant chemical re-

leased from mast cells is histamine, a small molecule that stimulates smooth muscle contraction

and vasodilation and irritates nerve endings, causing itching and pain. Histamine also increases

Clinical Signs of Localized Allergic Reactions

Depending on the amount and site at which these molecules are released, type I hypersensitivity

reactions can produce various clinical syndromes. Hay fever is localized to the upper respirato-

Clinical Signs of Systemic Allergic Reactions

When the inflammatory mediators exceed the body’s coping mechanisms, acute anaphylaxis or

anaphylactic shock may occur. This is a form of systemic shock in which violent constriction

Diagnosis of Type I Hypersensitivity

Clinicians diagnose type I hypersensitivity with a test that detects the amount of IgE directed

against an allergen. High levels of a specific IgE indicate a hypersensitivity against that allergen.

The tests are called ImmunoCAP Specific IgE blood test, CAP RAST, or Pharmacia CAP.

Prevention of Type I Hypersensitivity

Prevention begins with identification of an allergen and avoidance of that allergen. Avoidance

may require lifestyle and/or dietary changes. Some patients elect immunotherapy (“allergy

Treatment of Type I Hypersensitivity

For treating hay fever, antihistamines are administered. Asthma is treated with inhalants con-

taining glucocorticoid and a bronchodilator, which counteract the effects of many inflammatory

mediators. Epinephrine quickly neutralizes anaphylaxis.

Type II (Cytotoxic) Hypersensitivity

Type II hypersensitivity reactions result when cells are destroyed by an immune response, typi-

The ABO System and Transfusion Reactions

Some surface molecules of red blood cells, called blood group antigens, have many useful

functions and vary in complexity. The ABO group system, for example, consists of just two an-

tigens, A and B, and individuals can have either one (in which their blood type would be either

The Rh System and Hemolytic Disease of the Newborn

Rh antigens are proteins common to the red blood cells of 85% of humans as well as rhesus

monkeys. If an Rh-negative mother is pregnant with an Rh-positive fetus, fetal red blood cells

Instructor’s Manual for Microbiology with Diseases by Body System, 5e

Type III (Immune Complex–Mediated) Hypersensitivity

The formation of complexes of antigen bound to antibody (IgG), also called immune complex-

es, initiates several molecular processes, including complement activation. Normally, immune

complexes are removed from the body via phagocytosis. However, in type III hypersensitivity

Hypersensitivity Pneumonitis

Type III hypersensitivity reactions in the lungs cause a form of pneumonia called hypersensi-

tivity pneumonitis. Individuals become sensitized when minute mold spores or other antigens

Glomerulonephritis

Glomerulonephritis occurs when immune complexes circulating in the bloodstream are depos-

ited in the walls of the glomeruli, the minute blood vessels of the kidneys. Damage to the ves-

sels can result in kidney failure, as the glomeruli lose their ability to filter wastes from the body.

Rheumatoid Arthritis (RA)

Rheumatoid arthritis (RA) is both a type III hypersensitivity and an autoimmune disease. RA

commences when B cells secrete IgM that binds to certain IgG molecules. The IgM-IgG com-

Systemic Lupus Erythematosus (SLE)

Systemic lupus erythematosus (SLE), or lupus, is also both a type III hypersensitivity and an

autoimmune disorder. The immune system of the affected individual produces autoantibodies

Chapter 18 Immune Disorders

Type IV (Delayed or Cell-Mediated) Hypersensitivity

When certain antigens contact the skin of sensitized individuals, they provoke inflammation that

The Tuberculin Response

A good example of a delayed hypersensitivity reaction is the tuberculin response, generated

when tuberculin, a protein extract of Mycobacterium tuberculosis, is injected into the skin of an

Allergic Contact Dermatitis

Another example of a type IV hypersensitivity reaction is allergic contact dermatitis, which is

T cell–mediated damage to chemically modified skin cells, such as those that have contacted

Graft Rejection

Graft rejection is a special case of type IV hypersensitivity. Grafts are tissues or organs that

have been transplanted, either between sites within an individual or between a donor and a re-

cipient. These are of several types:

 In an autograft, tissues are moved to a different location within the same patient.

 In an isograft, tissues are moved between genetically identical individuals (identical twins).

Graft-Versus-Host Disease

Transplant recipients may suffer graft-versus-host disease when donated bone marrow T cells

recognize the recipient’s cells as foreign. Radiation therapy destroys the recipient’s leukemia or

Donor-Recipient Matching and Tissue Typing

The very high degree of MHC variability makes MHC compatibility hard to achieve. Even close

relatives may not have matching MHC antigens. Attempts to match donor and recipient tissues

The Actions of Immunosuppressive Drugs

Potent immunosuppressive drugs are used to increase the success of transplant procedures and

treat autoimmune disorders. Commonly used immunosuppressive drugs include glucocorti-

coids, commonly called corticosteroids or steroids, such as prednisone and methylprednisolone,

Autoimmune Diseases (pp. 534–536)

Autoimmune diseases are any of a group of diseases that can result when an individual begins

to make autoantibodies or cytotoxic T cells against normal body components.

Causes of Autoimmune Diseases

There are many theories concerning the cause of autoimmune diseases, which are far more

common in women than in men and tend to arise as an individual ages. These theories include

the following:

 Estrogen may stimulate the destruction of tissues by cytotoxic T cells.

Examples of Autoimmune Diseases

One group of autoimmune diseases involves only a single organ, tissue or cell type. Examples

include the following.

Chapter 18 Immune Disorders

Autoimmunity Affecting Blood Cells

Autoimmune hemolytic anemia is a disease that results when an individual produces antibod-

Autoimmunity Affecting Endocrine Organs

Type I (juvenile-onset) diabetes mellitus is an immunological attack on the islets of Langer-

hans cells resulting in the inability to produce the hormone insulin. Viral infection may trigger

Autoimmunity Affecting Nervous Tissue

Multiple sclerosis (MS) is a type IV hypersensitivity disorder in which cytotoxic T cells attack

and destroy the myelin sheath that insulates neurons. An infection may result in production of

Autoimmunity Affecting Connective Tissue

Rheumatoid arthritis is a crippling, autoimmune disease resulting from a type III hypersensitivi-

ty reaction in which autoantibodies are formed against connective tissue in joints.

Immunodeficiency Diseases (pp. 536–544)

Immunodeficiency diseases result from defective immune mechanisms and may be classified in-

to two types:

2. Acquired or secondary immunodeficiency diseases result from other known causes, such as

malnutrition, severe stress, or infectious disease.

Primary Immunodeficiency Diseases

One of the more important primary immunodeficiency diseases is chronic granulomatous dis-

ease, in which children have recurrent infections characterized by the inability of their phago-

cytes to destroy bacteria.

Some children fail to develop any lymphoid stem cells whatsoever and cannot mount any

type of immune response. The resulting immune defects cause severe combined immunodefi-

Instructor’s Manual for Microbiology with Diseases by Body System, 5e

Acquired Immunodeficiency Diseases

Previously healthy immune systems may become damaged in very old age and by severe stress,

malnutrition, or environmental toxins. Insufficient T cell production leads to an increased inci-

dence of viral diseases and certain types of cancer.