type I hypersensitivity

Which of the primary principal mediators involved in type I hypersensitivity causes an increase in vascular permeability and smooth-muscle contraction?

Histamine and 5-hydroxytryptamine (serotonin) both do this. Histamine is stored in the granules, and its biological effects occur within minutes of mast-cell activation. It makes up as much as 10% of the weight of mast-cell granules. Serotonin results in increased vascular permeability, smooth muscle contraction, and complement activation, enabling the migration of leukocytes.

How are immediate hypersensitivity reactions, such as those induced by an insect sting, treated and how does the treatment work?

Clinical signs and symptoms associated with this type of hypersensitivity are quickly terminated by administering epinephrine (also called adrenaline). The medication relaxes stomach cramps and stops itching and hive formation. Additionally, it prevents any further release of mediators by increasing cAMP levels in mast cells. Epinephrine is normally injected into the outer thigh and may be administered directly through the fabric if it is relatively light. If the site is rubbed, it improves absorption of the medication. Epinephrine causes the blood vessels to contract, cardiac output to increase, and bronchial tubes to relax, thereby preventing collapse of the vasculature and allowing the individual to breathe much more easily.

How would one prevent further recurrences of anaphylaxis due to bee stings?

A type of therapy known as hyposensitization is highly effective in reducing or eliminating hypersensitivity type reactions. Increasing doses of the allergen is repeatedly injected into the susceptible individual. One type of hyposensitization, venom immunotherapy has been reported as high as 100% efficacious in eliminating anaphylaxis due to bee stings. In this type of therapy, the dosage of venom is increased twice weekly and given as an inoculum for 20 weeks. The highest dosage is then given every four weeks for as many as five years. When this therapy is conducted subcutaneously there is an increase in TH1- driven reactions and a decrease in the TH2-driven IgE responses. TH1 cells produce IFN- , a cytokine that inhibits type I responses. A shift toward IgG production has been quantified and is thought to be due to competition for the same allergen.

How should a person that is susceptible to these types of hypersensitivities take precautions?

It is recommended that they carry self-injectable kits. Epi-pen and ana-kit are two common kits that are used. Epi-pen is an automatic syringe that delivers exactly 0.3 mg of epinephrine. Ana-kit is a syringe and two needles, each with 0.3-mg doses of epinephrine. Additionally, susceptible individuals need to refrain from going outside without shoes in order to avoid bees that are foraging on flora such as white clover, and they should wear barrier clothing in order to reduce exposure to insects. It is also advisable for these individuals to avoid wearing fragrances that may attract unwanted bees and to avoid areas where bees predominate, such as garbage containers.

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