It is define as the process of engulfment of solid particles by the cell, the cell performing this function are called as phagocytic cell.There are two main type of phagocytic cell –
1) PMNs -It appears in acute inflammatory response also called as “microphages”.
2) Monocytes– It appears in chronic inflammatory response also called as “macrophages”.
These cells produce several proteolytic enzyme that is- proteolytic collagenases, elastases, lipase etc. The microbe undergo the process of phagocytosis involve three steps-a) Recognition and Attachment, b)Engulfment, c) Killing and Degradation. A) Recognition and Attachment– Phagocytosis is initiated by expression of surface receptor on macrophages which recognize microorganism by mannose receptor or scavenger receptor. The process of phagocytosis progressed when the microorganism are coated with specific protein opsonin from the serum. Opsonin establish a bond between bacteria and cell membrane of phagocytic cell. The main opsonin present in serum is IgG,C3b,lectin. B) Engulfment- The opsonized particle bound to the surface of phagocyte is ready to engulfed. This is accomplised by formation of cytoplasmic pseudopod around the particle due to activation of actin filament beneath the cell wall, enveloping it in phagocytic vacuole, plasma membrane enclosing the particle breaks from the surface, so phagosome lies free into the cytoplasm. The phagosome fuse with lysosome and form “phagolysosome”. C) Killing and Degradation- The microorganism being killed by antibacterial substance and are degraded by hydrolytic enzyme.