Admission Test for Dental Hygiene (ATDH) Practice

Which type of hypersensitivity is usually temporary and reversible?

1. Type I

2. Type II

3. Type III

4. Type IV

The correct answer is: Type I

Type I hypersensitivity is characterized by an immediate allergic reaction that typically arises from the interaction between an allergen and IgE antibodies, leading to the release of histamine and other mediators from mast cells and basophils. This type of hypersensitivity is commonly associated with allergic reactions such as hay fever, asthma, and anaphylaxis. One key aspect of Type I hypersensitivity is that the reactions can be acute and often subside quickly once the allergen is removed or after a short course of treatment. This transient nature of the response is why it is considered temporary and reversible. In contrast, Type II and Type III hypersensitivities involve antibody-mediated reactions that can lead to more prolonged tissue damage and are often associated with conditions like autoimmune diseases and chronic inflammatory states. Type IV hypersensitivity is a delayed-type response mediated by T cells, which also does not resolve as quickly and may take hours to days to manifest after exposure to the antigen. Thus, the nature of Type I hypersensitivity, with its rapid onset and resolution, distinguishes it as the type that is usually temporary and reversible.