Makindo Medical Notes

🛡️ Phagocytes are immune cells that engulf and digest foreign particles, bacteria, and dead or dying cells. This process is called phagocytosis. They are crucial in defending against infection and maintaining tissue homeostasis.

🔎 Types of Phagocytes

• 🧪 Neutrophils :
  • Most abundant white blood cell.
  • 🚨 First responders to infection/injury.
  • Engulf and destroy bacteria & fungi.
  • Short-lived; form pus when they die.
• 🦠 Macrophages :
  • Derived from monocytes migrating into tissues.
  • Clear pathogens, dead cells & debris.
  • 📡 Present antigens to T cells.
  • Long-lived, tissue-resident.
• 🌐 Dendritic Cells :
  • Professional antigen-presenting cells (APCs).
  • Found in skin & mucous membranes.
  • 🚀 Initiate adaptive immune response.
• 🪱 Eosinophils :
  • Combat parasites 🪱 and allergy-related responses 🤧.
  • Engulf parasites, modulate inflammation.
• 💊 Basophils :
  • Involved in allergies & parasitic infections.
  • Release histamine & inflammatory mediators.
  • Less important for direct phagocytosis.

⚙️ Mechanism of Phagocytosis

• ➡️ Chemotaxis: Attracted to site of infection by cytokines/chemokines.
• 🧲 Adherence: Recognise & bind via receptors; opsonisation enhances binding.
• 🫴 Engulfment: Membrane surrounds target → phagosome.
• ⚡ Digestion: Phagosome + lysosome = phagolysosome; enzymes & ROS kill target.
• ♻️ Exocytosis: Waste expelled from cell.

🛡️ Role in Immune Response

• Innate Immunity: Rapid, non-specific defence via PRRs (pattern recognition receptors).
• Adaptive Immunity: Macrophages & dendritic cells present antigens to T cells → bridge innate & adaptive immunity.
• Inflammation: Release cytokines to recruit immune cells, orchestrating inflammation & healing.

⚠️ Clinical Significance

• 🦠 Infections: Essential against bacteria, fungi, parasites. Deficiency → recurrent infections.
• 🔁 Autoimmune Disease: Can damage host tissue by misdirected attack.
• 🔥 Chronic Inflammation: Overactivation → diseases such as rheumatoid arthritis, IBD.
• 🎗️ Cancer: Dual role: may attack tumours or promote tumour growth/metastasis.

📚 Summary

Phagocytes (neutrophils, macrophages, dendritic cells, eosinophils, basophils) are essential defenders of the immune system. Phagocytosis proceeds through chemotaxis ➡️ adherence ➡️ engulfment ➡️ digestion ➡️ exocytosis. They are key to innate immunity, antigen presentation, and inflammatory regulation. Understanding their roles aids in recognising infections, autoimmune disease, chronic inflammation, and cancer biology.