White Blood Cell Types: Functions and Roles in Immunity

White blood cells (leukocytes) are the immune system's cellular defenders. Five main types have specialized roles:

1. Neutrophils (50–70%)

• First responders to bacterial/fungal infection.
• Phagocytic: engulf and digest pathogens.
• Short-lived (hours to days); form pus.

2. Lymphocytes (20–30%)

• T cells: Cell-mediated immunity; kill infected/cancerous cells; regulate immune response.
• B cells: Produce antibodies for humoral immunity.
• NK cells: Innate killing of virus-infected and tumor cells.

3. Monocytes (5–10%)

• Circulate briefly, then become tissue macrophages.
• Phagocytosis, antigen presentation, cytokine secretion.
• Key in chronic inflammation and tissue repair.

4. Eosinophils (1–3%)

• Defense against parasites (helminths).
• Modulate allergic reactions (asthma, hay fever).

5. Basophils (<1%)

• Release histamine, heparin, leukotrienes.
• Initiate allergic/inflammatory responses.

Collaboration

These cells communicate via cytokines and direct contact, providing layered defense: innate (neutrophils, monocytes, eosinophils, basophils) and adaptive (lymphocytes). Dysregulation leads to immunodeficiency, autoimmunity, or malignancy.