Phagocytes: Your Body's Cellular Cleanup Crew

Phagocytes are white blood cells that engulf and destroy pathogens, dead cells, and debris — the frontline of innate immunity.

Major Types & Roles

Cell	Location	Key Features
Neutrophils	Blood, tissues (first responders)	60% of WBCs; short-lived (hrs–days); NETosis (DNA traps); pus former
Monocytes / Macrophages	Blood → tissues (all organs)	Long-lived (months–years); high capacity; antigen presentation; tissue repair
Dendritic Cells	Skin, mucosa, lymphoid organs	Specialized antigen capture → migrate to lymph nodes → activate T cells (bridge to adaptive)
Microglia	CNS	Brain-resident macrophages; synaptic pruning, neuroinflammation

Phagocytosis Steps

1. Recognition (PRRs bind PAMPs/DAMPs; opsonins: IgG, C3b)
2. Engulfment → phagosome formation
3. Phagolysosome fusion (lysosomal enzymes, ROS, RNS, low pH)
4. Digestion & antigen presentation (MHC II → CD4+ T cells)
5. Resolution: efferocytosis (clear apoptotic cells) → anti-inflammatory signals

Clinical Relevance

• Neutropenia (ANC <1500/µL) → bacterial/fungal infection risk.
• Chronic Granulomatous Disease: NADPH oxidase defect → recurrent catalase+ infections.
• Macrophage activation syndrome: Cytokine storm (HLH).
• Therapeutic targeting: CAR-macrophages, trained immunity.

Phagocytes are ancient, essential, and remarkably versatile — cleaning up yesterday so we can face tomorrow.