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):
Thomas P. Stossel (^ The Immune System, Peter Parham, Garland Science, 2nd edition
Ishimoto H, Yanagihara K, Araki N, et al. (July 2008). "Single-cell observation of phagocytosis by human blood dendritic cells". Jpn. J. Infect. Dis. 61 (4): 294–7. PMID 18653972.
Mukundan L, Odegaard JI, Morel CR, Heredia JE, Mwangi JW, Ricardo-Gonzalez RR, Goh YP, Eagle AR, Dunn SE, Awakuni JU, Nguyen KD, Steinman L, Michie SA, Chawla A. (2009)PPAR-delta senses and orchestrates clearance of apoptotic cells to promote tolerance.Nat Med. 2009 Nov;15(11):1266-72.
Brigham and Women's Hospital and Harvard Medical School), June 22, 1999