Allergy and its types
Allergy and its types:-
Allergy:-
> An allergy is an immunological hypersensitivity mediated by immunoglobulin E antibody (IgE).
> It is not related to any disease or infections.
> Allergies can be seen in many organs, but most commonly, they affect the skin and mucous membranes.
> Our body is sensitive to specific particles in the environment, and these particles are called allergens.
> Allergies are mostly a type of antigen that produces an abnormally vigorous immune response.
Types of Allergies:-
a. Type I:-
> This reaction is initiated by the antigen reacting with tissue mast cells passively sensitized by antibodies (IgE) elsewhere, leading to pharmacologically active mediator release.
> The reaction is manifested within seconds or minutes after exposure and referred to as immediate hypersensitivity.
> It includes general anaphylaxis and local manifestation of symptoms in various organs or systems.
> The examples include bronchial asthma, rhinitis, urticaria, vomiting, diarrhoea, etc.
b. Type II:-
> In this case the antibody (IgG/IgM) is directed against the antigen on an individuals’ own cells (target cells) or foreign antigen, e.g., transfused red blood cells.
> This may lead to cytotoxic action by killer cells or by complement mediated lysis.
> The examples are mismatched blood transfusion, transplant rejection, etc.
c. Type III:-
> In a type III reaction, antibodies (IgG and IgM) form complexes with antigen and complement, generating neutrophil generating factors.
> The immune complexes are deposited in the tissue.
> The complement cascade is activated and polymorphs are attracted to the site of deposition causing local damage.
> The examples include the Arthus reaction, serum sickness, etc.
d. Type IV:-
> This type of reaction is initiated by the action of antigen sensitized T-lymphocytes, releasing lymphokines following a secondary contact with the same antigen.
> Lymphokines induce inflammatory reaction and activate macrophages which release mediators.
> The reaction takes more than 12 hours to develop.
> The examples are tuberculin hypersensitivity, graft rejection, contact dermatitis, etc.