The consequences of Type I Hyper sensitivity reactions may be local or systemic.
Since mast cells are located in diverse areas of the body such as respiratory tract, gastro intestinal tract, reproductive tract and skin, exposure to allergen may lead to development of local responses like eczema, fever etc., or systemic response like asthma.
Generally the clinical symptoms of Type I hyper sensitivity reactions depend on the release of pharmacological products from mast cells and basophils.
The severity and area of the reactions depends on the number of mast cells stimulated, the amount of antigen administered, the route of administration etc. If small quantities of mild antigens are administered through intradermal injection, mild and localized reactions develop due to body’s response for harmonizing the changes developed under the influence of mast cell derived factors.
If a strong antigen in little large quantity is injected intravenously the reaction may be systemic and faster. Systemic anaphylaxis is a shock like condition and occurs in a very short time.
A wide range of antigens such as venom of bees, penicillin drugs, antitoxins, sea food, etc have been shown to trigger Type -1 hyper sensitivity reactions in humans.
Allergic rhinitis, hay fever, allergic bronchitis, vomiting, diarrhea, utricaria, atopic dermatitis etc. are some of the examples of Type I hyper sensitivity reactions.
Since Type I hypersensivity reactions are developed by humoral immunity, it can be transferred from an allergic person to other non allergic persons through serum transfer.
Since all the clinical signs of Type I hypersensitivity are related to the release of vasoactive substances from mast cells and basophils, the severity and site of the reactions depends on the number of mast cells stimulated, amount of antigens, and route of administration.
If the antigens are administered slowly in small quantities clinical signs would be very less. Because the individual gets an opportunity to balance the vascular changes provoked by the factors derived from mast cells.
Clinical Tests for Allergy
If a person is suspected to be allergic to any particular substance/allergen, it can be confirmed by simple wheal and flare test. In this clinical procedure a small dose of allergen is injected under the skin and the injected area is marked and studied in less than 30 minutes.
If the person is allergic to the injected allergen, a wheal and flare response at the site of infection is developed.
PK test or Prausnitz-Kustner procedure is one of the skin testing techniques for allergy, to detect reactive antibodies for specific antigens.
This test is based on repetition of intra dermal injection of serum from an allergic individual to non allergic person once in 24 hours, to observe inflammatory response. If the individual is positive (allergic) to that specific allergen, inflammatory response develops within 1 or 2 minutes.
This test can be carried to test certain life threatening allergens such as bee venom, scorpion venom etc.
The first step in therapy is identifying and stay away from contact with the allergens. Otherwise desensitization or immuno therapy with repeated injections of antigens in increasing doses (hyposensitization) can be done to reduce the strength of reactions in allergic people.
In this procedure repeated encounter with antigens may cause a shift in antibody production from IgE to IgG and the IgG antibodies may block or minimize binding of antigen with the mast cell bound IgE antibodies.
Use of anti histamines, to block histamine binding with the target cells through their receptors would work in the prevention of development of clinical symptoms.