Understanding Allergy and Hypersensitivity Reactions

Hypersensitivity

Exaggerated immune response to foreign agents.

Type I Hypersensitivity

Immediate IgE-mediated allergic reactions.

Type II hypersensitivity

non-IgE mediated(cytotoxic)

Type III hypersensitivity reaction

-Immune-Complex Reaction

-Local or systemic

-Immediate or delayed

Type IV hypersensitivity reaction

non-IgE mediated(cell mediated)

Anaphylaxis

Severe, life-threatening allergic reaction.

What is the most common hypersensitivity reaction?

Type I Hypersensitivity

How quickly do Type I Hypersensitivity reactions occur after exposure to an allergen?

Rapidly

What range of consequences can Type I Hypersensitivity reactions have?

From mild irritation to life-threatening (e.g., anaphylaxis)

What mediates Type I Hypersensitivity reactions?

IgE

What causes the pathological effects in Type I Hypersensitivity?

Release of inflammatory mediators (e.g., histamine) from mast cells and basophils

What are some examples of atopic disorders associated with Type I Hypersensitivity?

Asthma, eczema, urticaria

What hypothesis explains the increasing incidence of allergies?

The hygiene hypothesis

What does IgE mediate?

Allergic responses and parasite defense.

What type of parasites has IgE evolved to help eliminate?

Metazoan parasites, e.g., Ascaris and Schistosoma.

What immune cells help B-cells switch to IgE production?

CD4 T-cells (TH2).

How does the body physically expel parasites mediated by IgE?

Coughing, sneezing, vomiting, etc.

What cells are 'armed' by IgE to respond to parasite antigens?

Mast cells, eosinophils, and basophils.

What receptors do IgE bind to on immune cells?

High affinity Fc receptors.

what other roles does mast cells have in the immune system

responses at mucosal surfaces(they express TLR and other Fc receptors)

Mast Cells

Cells releasing inflammatory mediators in allergies.

Degranulation

Release of mediators from mast cells upon activation.

TH2 Cells

CD4 T-cells assisting B-cells in IgE production.

Immediate Reaction

Rapid response due to mast cell degranulation.

Late Phase Response

Delayed reaction involving mediator production and inflammation.

Atopic Eczema

Skin condition with genetic predisposition and allergens.

Urticaria

Red, itchy wheals caused by various allergens.

Pruritus

Itching caused by histamine on sensory neurons.

Systemic Anaphylaxis

Widespread mast cell activation causing shock.

Penicillin Allergy

IgE response to penicillin-peptide complexes.

Hapten

Small molecule that binds proteins, eliciting immune response.

Skin Prick Test

Initial test for identifying allergens, results in 20 minutes.

Hygiene Hypothesis

Theory explaining rising allergy incidence in developed countries.

Eosinophils

White blood cells involved in allergic responses.

Basophils

Cells releasing histamine during allergic reactions.

Vascular Changes

Alterations in blood vessels during allergic reactions.

Oedema

Swelling caused by fluid accumulation in tissues.

Allergic Reaction Symptoms

Range from mild irritation to severe reactions.

Genetic Predisposition

Inherited tendency to develop allergic conditions.

Specific IgE Test

Measures blood IgE levels in response to allergens.

Patch Test

Tests skin reactions to contact allergens.

Food Challenge

Gradual exposure to suspected food allergens.

Epinephrine

First-line treatment for anaphylactic shock.

Type II Hypersensitivity

Cytotoxic reactions mediated by IgG or IgM.

Haemolytic Anemia

Destruction of red blood cells due to antibodies.

Type III Hypersensitivity

Reactions involving immune complexes and IgG.

Arthus Reaction

Localized vasculitis from antigen-antibody complexes.

Serum Sickness

Systemic reaction from injected foreign serum proteins.

Oral Erythema Multiforme

Blistering of oral mucosa from immune complexes.

Type IV Hypersensitivity

Delayed T-cell mediated immune response.

Nickel Hypersensitivity

T-cell response to nickel altering peptide binding.

Contact Dermatitis

Skin reaction to lipid-soluble antigens.

Gell and Coombs Classification

Classifies hypersensitivity reactions into four types.

Anti-histamines

Block histamine receptors to alleviate allergic symptoms.

Hydrocortisone

Inhibits histamine synthesis in allergic reactions.

Cromoglycate

Stabilizes mast cells, preventing histamine release.

Hyposensitization

Allergen injections to shift IgE to IgG production.

Biphasic Response

Recurrence of symptoms after initial anaphylaxis resolution.

Complement Activation

Triggered by immune complexes leading to inflammation.

Fc Receptors

Bind antibodies to mediate immune responses.

Mast Cell Granules

Contain histamine and inflammatory mediators.

T-cell Activation

Initiates inflammatory response in Type IV reactions.

Intravenous Immunoglobulin

Used in severe allergic reactions for treatment.