Hypersensitivity microbiology notes


hello, doctor vanakam,
I hope you all are doing good, as intimated through the last post on anaerobic culture method https://www.stencildent.com/2020/08/anaerobic-culture-methods-microbiology.html if u haven't checked it out do read using this link without any further ado lets get started.


3)type 1 hypersensitivity reaction
a)1st exposure
b)2nd exposure
c)mediators of reaction
d)late-phase reaction
4)type 4 hypersensitivity


It refers to a condition in which immune response results in excessive reaction leading to tissue damage, disease, or even death in a sensitised host.


  • Coomb and gel classification in 1963 into type 1 to 4 
  • Type 1,    type 2, type 3       :
  • They depend on the interaction of antigen with humoral antibodies
  • They are the immediate-type reaction 
type 4 :
  • They are mediated by t lymphocyte
  • Delayed-type of hypersensitive reaction


  • They are involved with the IgE antibody , also called an IgE mediated type of reaction.
  • The most allergic reaction
  • An antigen that causes an allergic reaction: allergen
  • It occurs in 2 steps: 1)first exposure (sensitization), 2)subsequent exposure

a) first exposure  

  • eg)When a person inhales pollen after it enters there will be t cells against the pollen making the molecule allergen
  • Allergen picked by immune cells in airways migrate to lymph node
  • These are antigen-presenting cells like dendritic cells, macrophage that present to t helper cell
  • When a person is allergic it exhibits co-stimulatory molecule, before t cells seize antigen is called naive t helper 
  • When t cell bind to the antigen-presenting cell and co-stimulatory molecule is called primed t cell
  • In type 1 it converts to type 2 cell or t helper 2, interleukin (cytokine) help in conversion IL-4,IL-5, IL-10
  • B cell instead of making Ig M specific antibody it starts making IgE specific antibody
  • T helper 2 also release interleukin -5 that stimulate and activate eosinophil and release a toxic substance
  • Ig E specific to Fce receptor in mast cell gets attached they are called cytotrophic antibodies as they bind to  antigen surface

 b)2nd exposure:

Few months , later during 2nd exposure , the antibody binds to an antigen they get cross-link and degranulate pro-inflammatory mediators producing an allergic reaction.


  1. Histamine bind to h1 receptor resulting in bronchi smooth muscle to contract this further leads to difficulty in breathing and also because of blood vessel dilation , increase in permeability results in edema, urticaria
  2. Eosinophil
  3. Protease

d)late-phase reaction: 8-12 hours

Eosinophil,t helper 2 cells,and basophil are recruited to site where an allergen is located
mild symptoms are urticaria, eczema, allergic rhinitis 9inflammation in the nose , asthma
severe symptoms include increase n vascular permeability, airway constriction and may result in anaphylactic shock 


  • Its a delayed type of hypersensitivity, after 48-72 hours of exposure 
  • Cell-mediated response 
  • immune system elements are:
  • 1)Antigen-presenting cell
  • 2) Major histocompatibility class 2 
  • 3)Helper t cells: Based on glycoprotein present on the surface   
  • a)CD4+ glycoprotein they are known as helper t cells and present MHC class 2 
  • b) CD 8+ glycoprotein: they are known as killer t cells and present MHC class 1 
  • phases:
  1. Sensitization phase:
  • When an antigen enters our body it doesn't produce any reaction unless it binds to hapten and then causes an immune response 
  • When an antigen enters the body the dendritic cells engulf them and act as an antigen-presenting cell with the help of major histocompatibility complex class 2 on their surface its been recognized by cd 4 cells and t helper cell and secrete interleukin and results in proliferation of cd 4 cells.

2) Effector:

  • The proliferation of cd 4 cells results in the formation of interferon-gamma and activates macrophages and release  cytokines (tumor necrosis factor, interleukin) 
  • This gets activated by dd 8 cells and destroys the target organ.

 5) treatment:

1) Antihistamine: decrease in bronchoconstriction, and vascular permeability 
2)Corticosteroids: decrease the inflammatory response
3)Epinephrine: constrict the blood vessel 

Vanakam, today we have discussed about hypersensitivity reaction I would like to share my own experience on sensitivity all of us would be definitely allergic to some products like for me I am allergic to yam , turmeric I know u all might have got shocked, what? turmeric is considered to be antiseptic, how can u be allergic to it well I got your mind voice yes we do exist allergic to turmeric I googled about it in the net it was surprising to me to see that there are people with this allergic and I wasn't the only with this allergy.


 The next post is about thrombosis ; definition,factors favouring thrombus formation and fate of thrombus. I hope you all understood if it had helped you do let me know in the comment section below.
                                                     thank you


  1. You dentistry article is acedamic reference, i write general fun dental blog from Dentsma, thanks.

  2. This comment has been removed by the author.

  3. Thanks for sharing and explaining about antihypertensive medication Antihypertensive with peripheral action work by reducing or preventing the release of catecholamines from peripheral nerve endings.

  4. This post is so informative and makes a piece of very nice information best medical training institute/a>


Post a Comment

Popular posts from this blog

Sterilization technique in microbiology