Immune Surveillance by NK Cells and Phagocytes

Immune surveillance involves monitoring peripheral tissues to detect pathogens and infected or cancerous body cells.

Natural killer, or NK cells, which are non-phagocytic cells in the blood and lymph, use pattern recognition receptors or PRRs to recognize infectious organisms, cancerous cells, and infected body cells.

Upon binding the target cell, the NK cell is activated and realigns the maturing face of its Golgi apparatus, releasing secretory vesicles.

These vesicles contain glycoproteins like perforin, which form pores in the membrane of the target cell.

Through these pores, granzymes — protein-digesting enzymes secreted by NK cells, enter the target cell and trigger apoptosis.

In case the cell debris contains live intracellular pathogens, they are eliminated by phagocytes.

Neutrophils and macrophages are the two primary types of phagocytes. They use PRRs to identify pathogens.

After binding to its target cell, the phagocyte forms a pseudopod to engulf the foreign particle, trapping it inside a phagocytic vesicle.

Eventually, the vesicle fuses with a lysosome containing enzymes that can digest the invading particle.