Hypersensitivity reactions: Introduction, Classification and Types
- Types of hypersensitivity reactions
- It may be defined as undesirable reactions produced by normal immune system which includes allergies and autoimmunity.
Classification of hypersensitivity reactions
- Hypersensitivity reactions are classified traditionally into immediate and delayed type.
Immediate hypersensitivity (B cell or Antibodies mediated).
- Antibody mediated cell damage
- Arthus phenomenon
- Serum sickness
- T cell mediated.
- Infection type.
- Contact dermatitis type.
- Hypersensitivity reactions are inflammatory reaction within the humoral or cell mediated immune system death proceeds for tissue damage or death.
- They are localized reaction induced by non infectious antigen which are called allergens.
|Immediate hypersensitivity||Delayed hypersensitivity|
|Appears and recedes rapidly||Appear slowly, lasts longer|
|Induced by antigen or haptens by any route||Antigen or haptens intradermally or with Freunds reagent or by skin contact.|
|Antibody mediated reaction: In this type of hypersensitivity circulating Antibodies are present and they are responsible for Reactions.||Cell mediated reaction: Here circulating Antibodies are absent and they are not responsible for the Reactions.|
|Passive transfer is possible with the serum||Can’t be able to transfer with the serum|
|Desensitization easy but short lived||Difficult but it is long lasting|
Types of hypersensitivity
Hypersensitivity reactions is of four types:
- Hypersensitivity Type 1
- Hypersensitivity Type 2
- Hypersensitivity Type 3
- Hypersensitivity Type 4
- IgE or reagin dependent.
- Antibodies, cytotropic IgE antibodies are fixed on the surface of tissue cells (basophils and mast cell) in sensitized individual.
- Clinical complex of Type 1 reaction includes potential system and anaphylaxis and localized responses like hey fever and asthma.
Hypersensitivity Type- 2
- Cytotoxic or cell stimulating.
- These type of hypersensitivity reactions is initiated by IgG antibodies that may be reacts either with cell surface or tissue antigens.
- ADCC-antibody dependent cell mediated cytotoxic reaction.
- Cell or tissue damage occurred within the presence of complement or mononuclear cells.
- Type 2 reactions are intermediate between hypersensitivity and autoimmunity.
Hypersensitivity Type- 3
- Immune complex or toxic complex diseases.
- In this type of hypersensitivity reactions, antigen-antibody complexes are responsible for damages.
- These may precipitate in a round small blood vessel, causing damage to secondary cells or on membranes, interfering with their functions.
Hypersensitivity Type 4 (Delayed type hypersensitivity)
- Delayed or cell mediated hypersensitivity.
- Some cytokines like MCF, MIC and interferon – Gamma, are released from sensitized TH-1 cells and meditate the reactions.
- The release of cytokines makes accumulation of macrophages which produce lytic enzymes and causes the tissue damage along with neutralization of the poison or antigen.
|Type of Reactions||Clinical syndrome||Time required for manifestation||Mediators|
|Type 1: IgE type||
||Minutes||IgE, histamine and other agent|
|Type 2: cytolytic and cytotoxic||Antibody mediated damage, anemia, agranulocytosis etc.||Variable hours to days||IgG, IgM|
|Type 3: immune complex||
||Variable : hours to days||IgM, IgG,C and leucocytes|
|Type 4: delayed hypersensitivity||
||Hours to days||T- cells, lymphokines, macrophages.|
Reference and Sources
- 1% – https://en.wikipedia.org/wiki/Hypersensitivity
- 1% – https://emedicine.medscape.com/article/136118-overview
- 1% – https://www.slideshare.net/MartaGerasymchuk/metod-med-fty-1st-semester-book-2017-module-1
- 1% – https://www.studyblue.com/notes/note/n/nurse-pathophysiology-study-guide-2012-13-pittiglio/deck/9711393
- 1% – https://quizlet.com/170287342/immuno-4-flash-cards/