HYPERSENSITIVITY

DACIL & HARVI

What are the Two Types of Immune System?1. INNATEHOURS

◦ Epithelial Barriers◦ Phagocytes◦ Dendritic Cells◦ Complement◦ Natural Killer Cells

2. ADAPTIVEDAYS/MONTHS◦ B-LymphocytesANTIBODIES◦ T-LymphocytesEffector T

Cells

What is meant by the term HYPERSENSITIVITY?◦ An INAPPROPRIATE and EXCESSIVE immunological reaction to

an external antigen.

◦ The external antigen is usually called an ALLERGEN!

What is meant by the term Autoimmunity?◦ INAPPROPRIATE and EXCESSIVE immunological reaction to a

self-antigen/auto-antigen

◦Due to a dysfunctional control of the immune system.

TYPES OF HYPERSENSITIVITY REACTIONS

Type Name Mediators Examples

I Immediate or IgE mediatedAllergic

IgE + Mast cells

AllergiesAnaphylaxisAsthmaAtopy- genetic predisposition

II Antibody-dependentCytotoxic

IgM/ IgG Autoimmune haemolytic anaemia- Goodpasture’s syndrome- lung + kidney

Myasthenia GravisGrave’s disease

III Immune complexImmune complex deposition

IC Serum SicknessExtrinsic Allergic Alveolitis (EAA)Rheumatoid ArthritisSystemic Lupus Erythematosus

IV Delayed or Cell mediatedDelayed

T lymphocytes

Allergic Contact DermatitisChronic Transplant RejectionMSTuberculin Skin Test

AnGST

Type 1- Immediate/ IgE mediated

What is the process of type I?1. Sensitisation occurs first (IgE production & binding to mast

cells)

2. Thereafter exposure generates immediate response (degranulation)

Angioedema

Urtricaria- rash caused by fluid

leaking out of surface blood vessels. Hives/ wheals

 A 5 year old child is being brought to your dept after developing noisy breathing and a rash. He has respiratrory distress with a RR 50, Sats of 90% on high flow oxygen. Pulse is 140. CRT of 4 secs. The child is accompanied by his mother. He is having a nebuliser on route.The mother says she took her child to the GP this morning who prescribed some antibiotics. She gave these about half an hour ago. Within in a few minutes he became wheezy and complained of difficulty in breathing. He is not known to be allergic to anything. ◦ What is your immediate plan of action?

◦ ABCDE◦ Lie patient down◦ IV fluids

When performing your examination you notice the patient is pale, sweaty and has a generalised urtricarial rash, swelling around lips and eyes, and pyrexial at 38.2c

◦ What is your diagnosis?◦ Anaphylaxis

◦ What will you now give?◦ Adrenaline◦ IV chlorphenamine ◦ IV hydrocortisone◦ Nebulised salbultamol

◦ The child does not appear to improve over the next 5 minutes, what should you do?◦ Repeat adrenaline

◦ How is adrenaline given?◦ 500mcg IM

Tom’s girlfriend buys him a stylish watch for his birthday which he immediately puts on. Later, when she leaves he decides he doesn’t like it so decides not to wear it. However, a couple of days later she notices him not wearing it, so he decides to put it on. However, to his dismay Tomnotices the skin underneath the watch is becoming itchy and red, by the afternoon there are vesicles present.◦ What is the diagnosis?

◦ Allergic contact dermatitis

◦ What kind of hypersensitivity reaction is this?◦ Type IV (delayed/ cell mediated)

◦ What distinguishes this type of reaction to a Type I?◦ Slower and more specific/ localised

◦ To prove its type I can measure blood markers (IgE)

◦ How would the GP identify the exact allergen?◦ Skin patch testing

◦ What would be the first line of treatment for Tom?◦ Avoidance

◦ Metals e.g. nickel

◦ What other treatments are possible?◦ Anti-histamines- Topical Eye drops or Systemic Tablets

◦ Steroids- Topical Eye drops or Systemic Tablets

◦ Desensitisation- Allergen immunotherpay◦ Creates tolerances to allergens by small exposure gradually increasing sublingually or

subcutaneously.

THE END- THANKOOOO