**Question:** All are mononuclear-macrophages except ?

**Core Concept:** Mononuclear macrophages are a type of white blood cell that plays a crucial role in the immune system, particularly in phagocytosis and antigen presentation.

**Correct Answer: D.**

**Why the Correct Answer is Right:** Polymorphonuclear macrophages, also known as neutrophils, are a different type of white blood cell that shares some functions with mononuclear macrophages but is distinct in terms of cell structure and role in immune response. Mononuclear macrophages are characterized by a single large nucleus, while polymorphonuclear macrophages have multiple nuclei.

**Why Each Wrong Option is Incorrect:**

A. **Option A (Monocytes):** Monocytes are indeed mononuclear macrophages, contributing to phagocytosis and antigen presentation. This option is incorrect as it includes the correct type of macrophage.

B. **Option B (Eosinophils):** Eosinophils are another type of polymorphonuclear white blood cell, not mononuclear macrophages. They play a role in immune response but are distinct from mononuclear macrophages.

C. **Option C (Basophils):** Basophils are another type of polymorphonuclear white blood cell, similar to eosinophils and neutrophils. Like option B, basophils are not mononuclear macrophages.

D. **Option D (Polymorphonuclear macrophages):** As explained earlier, polymorphonuclear macrophages (polymorphonuclear leukocytes or neutrophils) are distinct from mononuclear macrophages and belong to a different category of white blood cells.

**Clinical Pearl:** Understanding the difference between mononuclear and polymorphonuclear macrophages is crucial for understanding the complexity and diversity of immune cells involved in the immune response. These cells play a vital role in phagocytosis, antigen presentation, and inflammation.

**Correct Answer Explanation:** Option D (Polymorphonuclear macrophages) is incorrect because it refers to polymorphonuclear leukocytes or neutrophils, which are polymorphonuclear macrophages and not mononuclear macrophages. The correct answer should be one of the other options (A, B, or C), representing mononuclear macrophages.