Patho: Chapter 12 (Disorders of the Immune response including HIV and AIDs)

Type I hypersensitivity reactions are commonly called _________.

Allergic reactions

What are Type I hypersensitivity reactions?

IgE-mediated reactions.

The antigens for Type I hypersensitivity reactions are called ________.

Allergens

The typical allergens are _____________.

Proteins in plant pollens, house dust mites, animal dander, foods, antibiotics like penicillins and sulfur drugs

Can type Type I hypersensitivity reactions be local or systemic?

Yes

How can a Type I hypersensitivity reaction be local or systemic?

It depends on the portal of entry of the allergen

What are the first steps of a Type I hypersensitivity reaction?

• Allergen activates TH2 cells

• TH2 cells stimulate B cells

• B cells differentiate into plasma cells

What happens after plasma cells are formed in a Type I hypersensitivity reaction?

• Plasma cells produce IgE antibodies

• IgE binds to mast cels and basophils (sensitization)

• Upon re-exposure, the allergen binds to IgE on mast cells

What happens when an allergen binds to IgE on mast cells?

• Mast cells degranulate

• Histamine and other inflammatory mediators are released

• An allergic reaction occurs.

What is anaphylaxis?

A systemic life-threatening response to the inflammatory mediators released during a Type I hypersensitivity reaction.

What causes anaphylaxis?

• Type I hypersensitivity reaction

• Release of inflammatory mediators from mast cells

• Exposure to an antigen through: Injection, skin exposure, and absorption through epithelial surfaces or GI mucosa

What are the characteristics/manifestations of anaphylaxis?

• Systemic allergic reaction

• Vascular shock due to vasodilation

• Bronchoconstriction

• Respiratory distress

What causes vascular shock during anaphylaxis?

Vasodilation caused by histamine and other inflammatory mediators

What causes respiratory distress during anaphylaxis?

Bronchoconstriction

What is a Type II hypersensitivity reaction?

An antibody-mediated cytotoxic hypersensitivity reaction in which IgG or IgM antibodies bind to tissue-specific antigens and trigger cell destruction, inflammation, or altered cell function.

What causes a Type II hypersensitivity reaction?

• Binding of IgG antibodies to tissue-specific antigens

• Binding of IgM antibodies to tissue-specific antigens

What are the characteristics/manifestations of a Type II hypersensitivity reaction?

• Cell destruction

• Tissue inflammation

• Altered cell function

• May affect RBCs, WBCs, or tissues

What are examples of Type II hypersensitivity reactions?

• Transfusion reactions

• Graves disease

• Goodpasture syndrome

• Myasthenia gravis

What is Graves disease?

An autoimmune disorder in which autoantibodies bind to and activate TSH (thyroid stimulating hormone) receptors, causing excessive thyroid hormone production (hyperthyroidism).

What causes Graves disease?

• Type II hypersensitivity reaction

• Autoantibodies bind to TSH receptors on thyroid cells

• Continuous activation of TSH receptors

• Excess thyroid hormone production

What are the characteristics/manifestations of Graves disease?

• Overstimulation of thyroid cells

• Excess thyroid hormone production

• Hyperthyroidism

What is immunodeficiency?

A disorder in which the immune system is unable to function normally, resulting in impaired immune responses.

What are the two types of immunodeficiency?

• Primary immunodeficiency

• Secondary (Acquired) immunodeficiency

What causes primary immunodeficiency?

Genetic defects affecting the immune system

What causes secondary (Acquired) immunodeficiency?

• Malnutrition

• Immunosuppressive drugs

• AIDS (HIV infection)

What are the characteristics/manifestations of immunodeficiency?

• Ineffective immune responses

• Increased susceptibility to infections

• Depending on the disorder, deficiencies of B-cells, T-cells, or both may be involved.

What are the primary (genetic) forms of immunodeficiency?

• Severe Combined Immunodeficiency (SCID)

• Wiskott-Aldrich syndrome

• Humoral (B-cell) deficiencies

• Cellular (T-cell) deficiencies

What are the secondary (acquired) forms of immunodeficiency?

• Malnutrition

• Immunosuppressive drugs

• AIDS

What is Human Immunodeficiency Virus (HIV)?

A retrovirus that infects CD4-positive T helper cells and macrophages, causing immunodeficiency.

What cells does Human Immunodeficiency Virus infect?

CD4-positive T helper cells and macrophages

What causes Human Immunodeficiency Virus (HIV)?

Transmission through infected body fluids:

• Sexual contact

• Breast milk

• Blood-to-blood contact

• Contaminated needles

• Blood transfusions

• Pregnancy or birth

What are the characteristics/manifestations of Human Immunodeficiency Virus (HIV)?

• Immunodeficiency

• Infection of macrophages

• Infection of CD4-positive T helper cells

• Reduction in CD4-positive T cell count

• May lead to AIDS

A person is considered to have AIDS when _________.

their CD4 count is less than 200 cells/mL or if they have an AIDS defining illness.

What is Acquired Immunodeficiency Syndrome (AIDS)?

A disease caused by infection with Human Immunodeficiency Virus (HIV) that results in severe immunodeficiency due to a reduction in CD4-positive T helper cells.

What causes Acquired Immunodeficiency Syndrome (AIDS)?

• Infection with HIV

• Reduction in CD-4positive T helper cells

• Progressive immune system dysfunction

What are the characteristics/manifestations of AIDS?

• Immunodeficiency

• Reduced CD4-positive T helper cell count

• Opportunistic infections

• May lead to failure to thrive

• May lead to severe infections

All of the following are true about Type I Hypersensitivity Reactions EXCEPT:

TH2 cells block the differentiation of B cells into plasma cells

A client is being treated for an anaphylactic reaction after eating shrimp. Which class of antibodies mediates the anaphylaxis?

IgE