Chapter 19

Hypersensitivity

Abnormal, undesirable response to antigen

Type 1 Hypersensitivity Reaction

Anaphylactic; IgE bind to mast cells + basophils by an antigen bridge —→ degranulation—> release of histamine—> hemotactic for neutrophils + eosinophils

• after that reaction you’ll get edema(the swelling that happens because histamine makes blood vessels leaky, so fluid escapes into tissues during an allergic reaction.)

• erythema( redness) due to the vasodilation

• In the lungs you’ll get smooth muscle contraction—> leading to asthma symptomps

• Relase of leukotrienes( what causes smooth muscle contraction in the lungs - asthma attack)

• Release of prostaglandins( leads to mucous secretion in lungs)

Type I: Anaphylactic ( allergic reaction)

• Fastest of the reaction (2-30)

• Systemic ( shock)

• Vasolidation——> drop in blood pressure

• Epinephrine can be used to cause vasoconstriction—> increase blood pressure

• Injection like bee stings= systemic anaphylactic

Local Anaphylactic

• Hives, hay fever, asthma

• Ingested or inhaled allergen

Prevention for Type I Anaphylactic

• Identify allergen

• allergy skin tests- wheals ( small affected area)

• desensitization: add increasing doses of the allergen in order to build a IgG antibodies instead of IgE

• IgG will bind before IgE—> ‘‘blocking antibodies

Type 2 Hypersensitivity Reaction

• Cytotoxic; IgM and IgG bind to cell surface antigen and activate complement system

• Cell associated antigen

• RBC: Type A,B, AB, O

• Rh-factor surface antigen: +: have, -: dont have. - only produce anti-Rh antibodies if Rh+ blood to someone who is Rh-

Type 2: Transfusion Reaction

Antibody-antigen reaction—> agglutination—complement—> hemolysis : this is killing the red blood cell, you DONT WANT TRANSUFSION REACTION! therefore only certain donors can receive certain blood types

Type 2: Hemolytic Disease of the Newborn (HDNB)

• Occurs when you have a mother that is Rh-

• First baby is Rh+

• Body later on the pregnancy, the body will make anti Rh antibodies

• Second baby is also Rh+

• That is when we get HDNB! —> anti-Rh antibodies to cross the placenta—> lead to hemolysis of the baby’s blood which can be fatal for the baby.

A mother who is Rh- can receive a shot of Rhogam to prevent HDNB

Type 3 Hypersensitivity Reaction

Immune complex, antigen- antibody complex, IgG; inflammatory response

Type 3 - Immune complex

• Dealing with soluble antigen in serum and not attached to cells

• Form antigen-antibody complexes—> go to organs—> lead to inflammation

• IgG

• Immune complexes are going to deposit in vessel walls—leads to activation of complement—> attracts inflammatory cells( neutrophils) —> able to release enzymes that cause damage of basement membrane

• example of that is glomerulonephritis- immune complex condition of kidneys

Type 4 Reaction

• Delayed cell-mediated

• T-cell response ( not antibodies)

• Transplant Rejection ( immune system recognizes a transplanted organ or tissue as foreign invader )

• MHC (HLA) = ‘‘self” surface antigen ( internal fingerprints)

• Foreign antigen is going to be phagocytosed by macrophage—> presented to TCR

• T-cells→ build memory T-cells → re-exposure→ activate memory T-cells → release of cytokines+ inflammation

• This is the basis of a TB skin test

• Poison ivy allergic, 1st time nothing happens, then 2nd time BOM you get a inflammation response ( T-cell mediated response)

Autoimmunity

Loss of self tolerance ( dont recognize your own cells)

• Defect in thymic selection ( loss of clonal deletion) ; bone marrow for B-cells

• Cytotoxic: Graves disease

• Immune complex: lupus, rheumatoid armritis

• Cell-mediated response: Multiple scorosis, diabetes mellitus

Immunodeficiencies

Absence of a sufficient immune response

• Congenital: primary immunodeficiency, born with

• Accquired: secondary immunodeficiency, drugs, cancer, infectious agent like a virus ( HIV) attacks CD4 + T-cells ( immune cell)