Allergy & hypersensitivity

1. Allergy
&
Hypersensitivity

2. Allergy
A disorder of the immune system often also referred to as atopy.
Strictly, allergy is one of four forms of hypersensitivity and is called type I (or
immediate) hypersensitivity.
Allergic reactions occur to normally harmless environmental substances known as
allergens.
Reactions are acquired, predictable, and rapid Include eczema, hives, hay fever,
asthma attacks, food allergy, and reactions to drugs and the venom of stinging insect
such as wasp and bees

3. Hypersensitivity Reactions
Excessive, undesirable (damaging, discomfort-producing and sometimes
fatal) reactions produced by the normal immune system.
Require a pre-sensitized (immune) state of the host
Gell-Coombs Classified the reactions into four types based on the mechanisms
involved and time taken for the reaction----
Type I, type II, type III and type IV
Produce tissue injury

4. Hypersensitivity Types & Immune Reactant
3 involve antibody-
Type I (immediate): mediated by IgE (Mast Cells)
Type II: mediated by IgG or IgM
Type III (immune complex disease): IgG & complement
One involves antigen specific cells-
Type IV: Delayed type hypersensitivity, cell- mediated immune memory
response.

10. INDUCTION AND EFFECTOR MECHANISMS IN
TYPE I HYPERSENSITIVITY

11. T-helper cells
Antigen presentation stimulates T cells to become either
"cytotoxic" CD8+ cells or "helper" CD4+ cells. TCR: T-cell
receptor
MHC proteins are only found on the surface of specialised
antigen- presenting cells (APCs).