Phagocytosis

description about phagocytosis

1. PHAGOCYTOSIS Dr. TULIKA CHAUDHARY

2. PHAGOCYTOSIS Phagocytosis is defined as the process of engulfment of solid particulate material by the cell. Phagocytosis is chiefly a defensive reaction against infection and invasion of the body by foreign substances ( antigens ).

3. PHAGOCYTES The white blood cells protects the body by ingesting harmful foreign particles, bacteria and dead cells. These cells helps in performing the process of phagocytosis and known as Phagocytes. There are 2 main type of phagocytic cells: Neutrophils macrophages

4. Neutrophil * Polymorphonuclear neutrophils helps in engulfment of foreign particles or bacteria and kill them by phagocytosis .

5. STAGES OF PHAGOCYTOSIS Attachment stage ( opsonisation ) Engulfment stage Secretion stage ( degranulation ) Killing or degradation stage

6. Attachment stage( Opsonization ) Opsonization refers to the process of coating of bacteria by opsinins by which bacteria become tasty to the phagocytes. IgG opsonin and its corresponding receptor on the surface of polymorphs and monocytes is Fc fragment of immunoglobulin. C3b opsonin fragment of complement and corresponding receptor for C3b on the surface of phagocytic cells.

7. ENGULFMENT STAGE The opsonized particle bound to the surface of phagocyte is ready to be engulfed. This is done by formation of pseudopods around the particle, enveloping it in a phagocytic vacuole. Pseudopods meet each other on opposite side and fuse, this create an enclosed chamber with the engulfed material.

8. SECRETION STAGE Once the bacteria is engulfed, the lysosomes pour their enzymes into the vesicles and also in interstitial space. This process is called degranulation . There are large number of enzymes geared up for digesting bacteria. Lysosomes of macrophages contain lipases which digest the thick lipid membranes possesed by certain bacteria.

9. KILLING STAGE The neutrophils and macrophages contain bactericidal agents which can kill most of the bacteria. The microorganism after killed by antibacterial sustances are degraded by hydrolytic enzymes,this mechanism fails to kill & degrade some bacteria like tubercle bacilli. The antimicrobial agents act by either of the following mechanism: Oxygen dependent mechanism Oxygen independent mechanism

10. Oxygen dependent mechanism It is important mechanism of microbicidal killing is by the production of reactive oxygen metabolites. Increased oxygen consumption with an increased formation of ROS- respiratory burst Increase in the activity of NADPH phagosome oxidase . NADPH- oxidase present in the cell membrane of phagosome reduce oxygen to superoxide ion. Oxygen is converted to superoxide ion , hydrogen peroxide , all of these are microbicidal agents.

11. OXYGEN INDEPENDENT MECHANISM Some agents released from the granules of phagocytic cells do not require oxygen for bactericidal activity. These include lysosomal hydrolases , permeability increasing factors , defensins and cationic proteins.