Q.86. Which ONE of following leucocytes is phagocytic and has clear cytoplasm?
(A) Eosinophil
(B) Monocyte
(C) TH-lymphocyte
(D) Basophil

The correct answer is: Monocyte (Option B). Monocytes are phagocytic white blood cells with comparatively clear, non-granular cytoplasm under the light microscope.

Question and correct answer

The MCQ asks: “Which one of the following leucocytes is phagocytic and has clear cytoplasm?”

• Eosinophils and basophils are granulocytes, so their cytoplasm is packed with prominent granules and does not appear clear.

• TH-lymphocytes (T‑helper cells) are lymphocytes mainly involved in immune regulation, not primary phagocytosis.

• Monocytes are agranulocytes with relatively clear cytoplasm and strong phagocytic activity, so they best match both conditions in the question.

Therefore, Monocyte (Option B) is the most appropriate choice.

Explanation of monocyte (correct option)

Monocytes are large agranular white blood cells that circulate in blood and then migrate into tissues, where they differentiate into macrophages and dendritic cells. Their cytoplasm appears relatively clear or lightly basophilic because they lack the dense, coarse specific granules seen in granulocytes.

Functionally, monocytes and their tissue derivatives are key professional phagocytes: they ingest and destroy bacteria, dead cells and debris, and present processed antigens to lymphocytes. This makes them central to both innate defense (phagocytosis) and initiation of adaptive immune responses.

Why eosinophil is incorrect (Option A)

Eosinophils are granulocytic leukocytes characterized by large, acidophilic (eosin-staining) cytoplasmic granules that give the cytoplasm a bright reddish‑orange granular appearance under the microscope. They do have some phagocytic capacity, but their primary role is in defense against helminthic parasites and in modulating allergic and hypersensitivity reactions via degranulation of toxic proteins and mediators.

Because the question specifically asks for a leucocyte that is phagocytic and has clear cytoplasm, eosinophils are unsuitable: their cytoplasm is prominently granular, not clear, so they do not fit the morphological criterion even though they can participate in phagocytosis to a limited extent.

Why TH‑lymphocyte is incorrect (Option C)

TH‑lymphocytes (T‑helper cells, a subtype of CD4⁺ T cells) are lymphocytes that coordinate immune responses by secreting cytokines and helping B cells, cytotoxic T cells and macrophages. Morphologically, small lymphocytes have a large, dense nucleus with a thin rim of pale cytoplasm, which may look clear, but they are not considered professional phagocytes.

Their main function is immunoregulation and “helping” other cells, not engulfing and digesting pathogens or debris. Hence, despite their sometimes clear cytoplasmic rim, TH‑lymphocytes fail the functional requirement of being a phagocytic leukocyte, so this option is incorrect.

Why basophil is incorrect (Option D)

Basophils are granulocytes with large, coarse basophilic granules that often obscure the nucleus under light microscopy. These granules contain histamine, heparin and other mediators involved in inflammatory and allergic reactions, especially in IgE‑mediated hypersensitivity.

Basophils are not primary phagocytic cells; instead, they act mainly through degranulation and mediator release. In addition, their cytoplasm is heavily packed with dark granules, so it certainly does not appear clear. Therefore, basophils do not fulfill either the morphological (clear cytoplasm) or functional (phagocytic) requirement of the question.

Key points for exam preparation

• The most important professional phagocytes in blood are neutrophils and monocytes; in tissues, monocyte‑derived macrophages dominate.

• Granulocytes (neutrophils, eosinophils, basophils) show prominent cytoplasmic granules; agranulocytes (lymphocytes, monocytes) have relatively clear cytoplasm with no prominent specific granules.

• Among the options given, monocyte is the only leucocyte that is both clearly phagocytic and typically described as having clear (agranular) cytoplasm, making it the correct MCQ answer.