Hypersensitivity 

Hypersensitivity simply means allergy.  It is defined as the violent reaction of the immune system leading to severe symptoms and even death in a sensitized animal when it is re - exposed to the same antigen for the second time.  The factors causing hypersensitivity are called allergens.  In clinical terms, hypersensitivity is called allergy.  A familiar example for hypersensitivity is the allergy caused by penicillin injection.  Sometimes, in hospitals a patient dies immediately after penicillin injection.  This is due to allergy.  The allergy caused by drugs is called drug allergy.  The immune system is devised by nature primarily to protect the human body against pathogens.  Sometimes this system becomes overenthusiastic, and brings discomfort.  This phenomenon is similar to the overenthusiastic servant who tried to kill the fly sitting on the king's nose with a strong sharp knife.  Immune response is always directed towards the protection of host.  But in hypersensitivity the immune response becomes injurious to the host.  Hence the immune response becomes a destructive process in hypersensitivity.  In protective immune response, the antigen or bacterium or virus is killed or neutralized.  But in hypersensitivity, the cells of the host are killed or the last itself is damaged or killed.  Hypersensitivity is the changed reactivity of the immune system.  It is a beneficial protective system gone out of order.

Hypersensitivity does not occur in all human beings. Only about 10% of human population suffer from hypersensitivity.

 Hypersensitivity can bring its symptoms either immediately within minutes or in a delayed state, after 24 to 48 hours.

 Factors Causing Hypersensitivity

 Hypersensitivity is caused by numerous factors. These factors causing al lergy are called allergens. They may be extrinsic factors (introduced into the body from outside) or intrinsic factors (factors which remain within the body). They are the following: U A jak och

 1. Drugs such as penicillin, sulphamide, aspirin, etc .

2. Airborne particles such as pollen grains, house dust mite, spores, animal danders (scales and feathers of animals), etc. 

 3. Food stuffs such as shell fish, strawberries, brinjal, etc. 

 4. Infectious organisms like bacteria, viruses, fungi, parasite, etc. 

 5. Blood transfusion of mismatched blood.

 Symptoms 

Diarrhoea and vomiting Atopy 

• Rashness 

• Itching

 • Joint pain

• Malaise

•  Hypotension 
• "Abdominal pain Lymphadenopathy
• Swollen lymph nodes
•  Splenomegaly
•  Endocarditis 
•  Glomerulonephritis 
• Vasculitis 

• Odema

 Vasodilatation. 

Highlights 

Hypersensitivity violent reaction of the immune system leading to severe symptoms and even death in a sensitised animal when it is re exposed sensitivity  the same antigen for the second time.

 Hypersensitivity is the allergy. 

The factors causing hypersensitivity are called allergens. 

In hypersensitivity, the cells of the host are killed or the host itself is damaged or killed.  . 

• Hypersensitivity is caused by extrinsic factors or intrinsic factors. They are the following: 

• Drugs 
• Airborne particles
• Food stuffs Infectious organisms 
• Blood transfusion.

 • Hypersensitivity or Delayed hypersensitivity,

 Based on the different mechanisms of pathogenesis it is classi fied into  5 types: 

Type I: Anaphylact  ic hypersensitivity 

Type II: Antibody - dependent cytotoxic hypersensitivity 

Type III: Immune complex - mediated hypersensitivity 

Type IV: Cell - mediated hypersensitivity

 Type V: Stimulatory hypersensitivity 

• The reactions caused in hypersensitivity may be local reactions or systemic reactions.

When the symptoms appear in a restricted area the reaction is called   local.

 When the symptoms affect all the organ systems of the body, theis called systemic.

The following are the common hypersensitivity reactions and disases:

•  Anaphylaxis
•  Transfusion reactions
•  Erythroblastosis foatalis
•  Arthus reaction 
• Serum sickness 
• Mantoux reaction
•  Contact dermatitis 
• Grave's diseases 
• Leprosy
•  Small pox 
• Measles
•  Herpes 
• Graft rejection 
• Candidiasis
•  Leishmaniasis
•  Bacterial  thyroiditis 
• Autoimmune glomerulonephritis
•  Mysthenia gravis.