Question
Classify the five types of WBCs (leukocytes). For each type, describe the nucleus shape, staining properties, percentage in blood, and primary function. Which WBC type is most abundant? Which is involved in allergic reactions?
(NEET + CBSE Board pattern)
Solution — Step by Step
WBCs are classified into:
- Granulocytes — have granules in cytoplasm: Neutrophils, Eosinophils, Basophils
- Agranulocytes — no visible granules: Monocytes, Lymphocytes
| WBC Type | Group | % in Blood | Nucleus Shape | Function |
|---|---|---|---|---|
| Neutrophils | Granulocyte | 60-70% | Multi-lobed (3-5 lobes) | Phagocytosis of bacteria — first responders |
| Eosinophils | Granulocyte | 2-3% | Bilobed | Combat parasitic infections, allergy modulation |
| Basophils | Granulocyte | 0.5-1% | S-shaped/bilobed (often obscured by granules) | Release histamine, involved in allergic responses |
| Monocytes | Agranulocyte | 6-8% | Kidney-shaped | Phagocytosis (become macrophages in tissues) |
| Lymphocytes | Agranulocyte | 20-25% | Large, round | Immune response — B cells (antibodies), T cells (cell-mediated) |
- Most abundant WBC: Neutrophils (60-70%)
- Largest WBC: Monocytes
- Smallest WBC: Lymphocytes (though they have the largest nucleus-to-cytoplasm ratio)
- Allergic reactions: Basophils and Eosinophils — basophils release histamine, eosinophils modulate the response
- Antibody production: Lymphocytes (specifically B-lymphocytes)
The names come from their staining behaviour with acidic and basic dyes:
- Neutrophils: stain with both acidic and basic dyes (neutral staining)
- Eosinophils: stain with eosin (acidic dye) — granules appear red/orange
- Basophils: stain with basic dyes (like methylene blue) — granules appear blue/purple
graph TD
A[WBCs - Leukocytes] --> B[Granulocytes]
A --> C[Agranulocytes]
B --> B1["Neutrophils 60-70%"]
B --> B2["Eosinophils 2-3%"]
B --> B3["Basophils 0.5-1%"]
C --> C1["Monocytes 6-8%"]
C --> C2["Lymphocytes 20-25%"]
B1 --> D["Phagocytosis"]
B2 --> E["Anti-parasitic"]
B3 --> F["Histamine release"]
C1 --> G["Macrophages"]
C2 --> H["B cells + T cells"]
style A fill:#fbbf24,stroke:#000,stroke-width:2px
style B1 fill:#86efac,stroke:#000Why This Works
The five WBC types represent a division of labour in the immune system. Neutrophils are the foot soldiers — they arrive first at infection sites and engulf bacteria. Eosinophils handle parasites (too large for phagocytosis — they release toxic granules instead). Basophils are like alarm bells — they release histamine to increase blood flow and recruit more immune cells. Monocytes are the heavy artillery — they become macrophages that clean up dead cells and present antigens. Lymphocytes are the intelligence network — B cells produce antibodies, T cells coordinate the attack.
Common Mistake
Students frequently confuse basophils with mast cells. Basophils circulate in blood; mast cells reside in tissues (skin, respiratory tract, gut). Both release histamine during allergic reactions, but they are different cell types. NEET may ask: “Which blood cell releases histamine?” — the answer is basophils (not mast cells, since mast cells are tissue-resident, not blood cells).
Mnemonic for WBC abundance order: “Never Let Monkeys Eat Bananas” — Neutrophils (60-70%) > Lymphocytes (20-25%) > Monocytes (6-8%) > Eosinophils (2-3%) > Basophils (0.5-1%). This order appears in NEET almost every year.