The most important cells in type I hypersensitivity:
**Core Concept**
Type I hypersensitivity, also known as immediate hypersensitivity, is an allergic reaction mediated by IgE antibodies. This reaction involves the activation of mast cells and basophils, leading to the release of histamine and other chemical mediators.
**Why the Correct Answer is Right**
The correct answer is mast cells and basophils. These cells play a crucial role in type I hypersensitivity reactions by releasing histamine and other chemical mediators when IgE antibodies bind to their Fcε receptors. This binding causes the degranulation of mast cells and basophils, leading to the symptoms associated with allergic reactions, such as vasodilation, increased vascular permeability, and smooth muscle contraction. The histamine released from these cells also stimulates the release of other chemical mediators, such as leukotrienes and prostaglandins, which contribute to the allergic response.
**Why Each Wrong Option is Incorrect**
**Option A:** Neutrophils are not typically involved in type I hypersensitivity reactions, as they are more commonly associated with phagocytic activity and the inflammatory response.
**Option B:** T cells, particularly T helper 2 cells, play a role in the regulation of the immune response and the production of IgE antibodies, but they are not the primary effector cells in type I hypersensitivity reactions.
**Option C:** Eosinophils are involved in the late phase of allergic reactions, particularly in asthma and atopic dermatitis, but they are not the most important cells in type I hypersensitivity reactions.
**Clinical Pearl / High-Yield Fact**
Mast cells and basophils are the primary effector cells in type I hypersensitivity reactions, and their activation leads to the release of histamine and other chemical mediators, causing the symptoms associated with allergic reactions.
**Correct Answer:** C. Mast cells and basophils.