Phagocytosis

Phagocyosis is the process of engulfment and digestion of microorganisms performed by macrophages & microphages.

The macrophages:

These cells originate from bone marrow promonocytes; after circulating in blood for few hours they migrate to tissues and constitute the mononuclear phagocyte system. They have been given specific names in accordance with their residing tissues; in lungs ; alveolar macrophages, in  liver ; kupffer cells, microglial cells in brain, mesangial cells in kidney and in bone as osteoclasts.

Macrophages are capable of ingesting and digesting exogeneous antigens such a s whole microorganisms and insoluble particles and endogeneous matter such as injured or dead cells. Macrophages act by process of chemotaxis in which they get attract towards variety of substances. In the next step antigen adheres to the cell membrane of macrophage. Adherence induces the protrusions called Pseudopodia to extend around the attached antigen. Fusion of pseudopodia encloses the antigen with in membrane bound structure called Phagosome which then enters the phagocytic processing pathway. Here Phagosome fuses with the lysosome and makes phagolyosome. Lysome has hydrolytic enzymes which digest the ingested material. The digested contents are then released through the process of exocytosis.

It has been found that phagocytosis of antigen can be enhances many times in the presence of specific antibody; so antibody functions as opsonin; a molecule that binds to antigen and macrophage and enhance the process of engulfment. This whole process whereby antigens are rendered more susceptible to phagocytosis is called as opsonisation.

for further reads:::

kuby's immunology