Which of the following is an example of a Type I hypersensitivity reaction?

A Type I hypersensitivity reaction, also known as an immediate hypersensitivity reaction, is primarily associated with the actions of IgE antibodies and the activation of mast cells and basophils. This type of reaction typically occurs rapidly after exposure to an allergen and can lead to various clinical manifestations, such as allergic rhinitis, asthma, anaphylaxis, and urticaria (hives).

In this context, asthma fits the characteristics of a Type I hypersensitivity reaction. It can be triggered by allergens such as pollen, dust mites, or pet dander, leading to symptoms that range from wheezing and coughing to difficulty breathing. The underlying mechanisms involve IgE-mediated degranulation of mast cells, resulting in the release of inflammatory mediators such as histamine, which contribute to airway contraction and inflammation.

The other options in the question involve different immunological processes. Transplant rejection typically involves a Type IV hypersensitivity reaction, which is mediated by T cells rather than antibodies. Contact dermatitis is also a Type IV hypersensitivity reaction, characterized by delayed allergic responses to contact allergens, leading to skin inflammation. Tubercular caseous necrosis is associated with a granulomatous reaction, primarily mediated by cell-mediated immunity rather than by IgE and mast cells