There are approximately 50 billion white blood cells in our bodies and that one of their functions is to engulf foreign cells. Here we see a white blood cell chasing bacteria which it eventually engulfs by the process Phagocytosis.
Phagocytosis in mammalian immune cells is activated by attachment to Pathogen-associated molecular patterns (PAMPS), which leads to NF-κB activation. Opsonins such as C3b and antibodies can act as attachment sites and aid phagocytosis of pathogens.
Engulfment of material is facilitated by the actin-myosin contractile system. The phagosome of ingested material is then fused with the lysosome, leading to degradation.
References (for phatocytosis only):