From the Guidelines
The four types of hypersensitivity reactions are Type I, Type II, Type III, and Type IV, as classified by Gell and Coombs, with distinct mechanisms and examples, including anaphylaxis, haemolytic anaemia, serum sickness, and allergic contact dermatitis, respectively. These reactions can be described as follows:
- Type I: IgE antibody-mediated reactions, such as anaphylaxis, which can be life-threatening and require immediate medical attention 1.
- Type II: Antibody-mediated cytotoxic reactions, including haemolytic anaemia and thrombocytopaenia, which can lead to significant morbidity and mortality if not properly managed 1.
- Type III: Immune complex-mediated hypersensitivity, exemplified by serum sickness and vasculitis, which can cause significant inflammation and tissue damage 1.
- Type IV: Delayed T cell-mediated responses, such as allergic contact dermatitis and psoriasis, which can impact quality of life and require ongoing management 1. It is essential to understand these different types of hypersensitivity reactions to provide appropriate diagnosis and treatment, minimizing morbidity, mortality, and improving quality of life 1.
From the Research
Hypersensitivity Reactions
The four types of hypersensitivity reactions are:
- Type I: immediate or IgE mediated 2, 3
- Type II: cytotoxic or IgG/IgM mediated, which can be further divided into type IIa and type IIb 2
- Type III: IgG/IgM immune complex mediated 2, 3
- Type IV: delayed-type hypersensitivity or T-cell mediated, which can be further divided into four categories: type IVa, type IVb, type IVc, and type IVd 2
Subcategories of Type IV Hypersensitivity Reactions
The subcategories of type IV hypersensitivity reactions are:
- Type IVa: CD4(+)Th1 lymphocyte mediated with activation of macrophages 2
- Type IVb: CD4(+)Th2 lymphocyte mediated with eosinophilic involvement 2
- Type IVc: cytotoxic CD8(+) T lymphocyte with involvement of perforin-granzme B in apoptosis 2
- Type IVd: T-lymphocyte-driven neutrophilic inflammation 2
Clinical Significance
These hypersensitivity reactions can occur simultaneously in some diseases, making diagnosis and treatment challenging 3. Understanding the different types of hypersensitivity reactions is essential for improved diagnostics and therapeutic interventions 3, 4.