Diagnosis of Immediate hypersensitivity

What are the three properties of the immune response?

• antigen receptors that recognize a wide range of pathogens

• immune memory to produce rapid recall IR

• tolerance to prevent autoimmunity

With a hypersensitivity reaction, the _____ is harmful not the ____

the immune response is harmful not the antigen

What is a hypersensitivity reaction?

an exaggerated or inappropriate IR to a benign antigen

What hypersensitivity is this?

antigen (allergen) induces IgE antibody that binds to mast cels and basophils

when exposed to the alergen again, the allergen cross-links the bound IgE on those cells. This causes degranulation and release of mediators (like histamine)

Type I

What hypersensitivity is this?

IgG mediated

antibody binding to cell membrane antigens leads to complement-mediated lysis of the cells or autoimmune hemolytic anemia

Type II

What hypersensitivity is this?

antigen-antibody immune complexes are deposited in tissues and neutrophils are attracted to the site. They release lysosomal enzymes, causing tissue damage (if IgG or IgM are involved then complement is also involved)

Type III

What hypersensitivity is this?

T cell mediated, not antibodies

CD4 and/or CD8 T cells are sensitized by protein antigens. Memory T cells release cytokines upon second contact with the same antigen

Type IV

What hypersensitivity is this?

examples: uticaria (hives), asthma, hay fever, allergic rhinitis, pollen, latex gloves, medications, bee stings, food, atopic dermatitis (eczema)

Type I

What hypersensitivity is this?

examples: hemolytic anemia, thrombocytopenia, blood transfusions (ABO transfusion reactions), rheumatic fever

Type II

What hypersensitivity is this?

examples: systemic lupus erythematosus, rheumatoid arthritis, serum sickness

Type III

What hypersensitivity is this?

examples: contact dermatitis, poison oak/ivy, TB skin test, SJS, drug rash

Type IV

Explain the relationship between angioedema and hypersensitivity reactions

angioedema can be a symptom of hypersensitivity, but it can also be its own disease (hereditary and aquired types)

Hereditary angioedema is characterized by what?

C1 esterase inhibitor deficiency (type 1) or C1 esterase inhibitor functional abnormality (type 2)

What are some signs of allergies? (remember signs are what we see on exam while symptoms are what the pt presents with)

turbinate hypertrophy, lymphoid hyperplasia, allergic conjunctivitis

What are some signs of allergics asthma? (remember signs are what we see on exam while symptoms are what the pt presents with)

barrel chest, prominent ribs, signs of labored breathing (like seeing the intercostal muscles contract)

What are some routine lab tests we can run to evaluate hypersensitivity reactions?

CBC, nasal or chest secretions, urine analysis (UA) or stool sample, and immuniglobulin levels (look for increased eosinophils with most of these)

What are some in vivo tests we can run to evaluate hypersensitivity reactions?

these are tests done on/to the pt

skin test (prick, patch, etc.) and respiratory test

What are some in vitro tests we can run to evaluate hypersensitivity reactions?

these are done by taking blood and testing it in the lab

RAST, ImmunoCAP (note: they have panels for different regions)

Patch testing is an example of a _____ hypersensitivity

type IV

What are some ways we manage anaphylaxis

assess and manage airway, breathing, circulation

admin EPIand provide supportive care (even if pt has epipen you still go to the ER)

place in recumbent position and elevate the lower extremities

What are some signs of atopy?

allergic salute (can cause a crease to form across bridge of nose) edema, dark under eyes (allergic shiner), “allergic facies”

How does atopic dermatitis (eczema) present in darker skinned pts?

hyper or hypopigmentation, and follicular prominence

What is atopy?

a genetic predisposition to develop IgE-mediated hypersensitivity reactions to common environmental allergens

we see the allergic tetrad: eczema, allergic rhinitis, extrinsinc asthma, and food allergy

How can we distinguish angioedema from angioedema related to a hypersensitivity reaction?

angioedema not associated with a hypersensitivity reaction is not mediated by histamine or IgE and does not cause hives

Explain the two phases of the Type 1 hypersensitivity reaction:

Two Phases of Response:

1. Immediate Phase (minutes): Histamine-mediated; vasodilation, edema, pruritus

2. Late Phase (2–12 hrs): Eosinophil and mononuclear infiltration, cytokine release → tissue damage, sustained inflammation