**Question:** The eosinophils secrets all EXCEPT-

A. histamine
B. leukotrienes
C. cytokines
D. prostaglandins

**Core Concept:** Eosinophils are a type of white blood cell that plays a crucial role in the immune system, particularly in combating parasitic infections. They are part of the adaptive immune response and are activated upon recognition of specific antigens. Eosinophils release various substances upon activation, including granule proteins, cytokines, and chemokines.

**Why the Correct Answer is Right:** Eosinophils primarily release granule proteins (such as major basic protein, eosinophil cationic protein, eosinophil-derived neurotoxin, and eosinophil peroxidase) upon activation. These proteins contribute to the destruction of parasites and modulation of the immune response. Histamine, leukotrienes, and prostaglandins are substances released by other cell types, particularly mast cells and immune cells involved in inflammation, not eosinophils. Cytokines are a broad group of signaling molecules, including interleukins and interferons, which regulate immune response and cell differentiation.

**Why Each Wrong Option is Incorrect:**

A. Histamine: Histamine is released by mast cells, not eosinophils. Histamine is involved in inflammation, vasodilation, and increased vascular permeability.

B. Leukotrienes: Leukotrienes are released by mast cells and basophils, not eosinophils. They contribute to inflammation, bronchoconstriction, and increased vascular permeability.

C. Cytokines: Cytokines are released by various immune cells, including T-cells, B-cells, and macrophages. They play a crucial role in immune response, inflammation, and cell differentiation.

D. Prostaglandins: Prostaglandins are released by various cell types, including immune cells, endothelial cells, and smooth muscle cells. They are involved in inflammation, pain, fever, and platelet aggregation.

**Clinical Pearl:** Understanding the specific substances released by different immune cells is essential for understanding the immune response and its regulation. Mast cells, basophils, eosinophils, and other immune cells release specific substances that contribute to inflammation, immune response, and tissue remodeling.

**Correct Answer:** D. Prostaglandins

**Why Each Wrong Option is Incorrect:**

A. Histamine: Histamine is involved in inflammation, vasodilation, and increased vascular permeability, but it is not a substance primarily released by eosinophils.

B. Leukotrienes: Leukotrienes contribute to inflammation, bronchoconstriction, and increased vascular permeability, but they are released by mast cells and basophils, not eosinophils.

C. Cytokines: Cytokines are released by various immune cells, including T-cells, B-cells, and macrophages. They play a crucial role in immune response, inflammation, and cell differentiation.

D. Prostaglandins: Eosinophils are part of the immune response and release specific substances like eotaxin,