Phagocytosis is simply the immunological process mediated by some immune system cells such as macrophages and neutrophils engulf or ingest bacteria and other particulate materials. These cells of the immune system whose main function is to eat or engulf bacteria are generally known as phagocytes. Phagocytes attack and engulf exogenous bacteria and other extracellular particles; and they also ingest and digest other insoluble particles and endogenous materials. The biological significance of phagocytosis in immune response was first explained by Elie Metchnikoff (1845-1916), a Russian scientist– who coined the phrase “phagocytes” to describe some type or group of white blood cells (WBCs) that engulf or eat pathogenic bacteria and other large complex molecules during phagocytosis.
Phagocytosis is a significant biological phenomenon during immune response; and it helps to localize and restrain pathogenic bacteria and other foreign bodies that invaded the host from further expression of their pathogenic activity in vivo. Though a well established innate immune response, phagocytosis also facilitates the cell-mediated immunity since some phagocytic cells (e.g. dendritic cells) helps in antigen presentation to the MHC complex molecules i.e. Class I MHC and Class II MHC molecules depending on the type of antigenic molecule being processed.
The process of phagocytosis ensures that ingested bacteria and other particulate materials are properly digested by specialized enzymes (e.g. lysozymes) and then released or eliminated from the body. Phagocytosis is generally an innate immune response that ingests and degrades bacteria and other extracellular materials. During phagocytosis, the plasma membrane of the phagocytic cells (e.g. macrophages) expands and engulfs the microorganism to form a large vesicle known as the phagosome; and degradative enzymes (e.g. lysozymes) present in the phagosome ensures that the ingested bacteria is efficiently degraded or digested before being eliminated from the host’s body. Phagocytosis is a multifaceted immunological process that involves several processes and these stages of phagocytic action during immune response shall be elucidated in this section.
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