Question

Describe the stages of phagocytosis. Explain how toll-like receptors and pathogen associated molecular patterns are involved in the process of phagocytosis. list any organelles involved in the process.

Answer 1

Answer-The stages of phagocytosis--i)Activation of the Phagocyte-Reating phagocytes are activated by inflammatory mediators such as bacterial products.As a result ,the circulating phagocytes produce surface glycoprotein receptors that increase their ability to adhere to the inner surface of capillary walls,enabling to squeeze out of the capillary and be attracted to the site of infection.in addition they produce pamp or pattern associated molecular patterns. II)Chemotaxis-chemotaxis is the movement of phagocytes toward an increasing concentration of some attractant such as bacterial factors.iii)Attachment of the phagocyte to the microbe or cell-Attachment of microbes is necessary for ingestion and it may be unenhanced or enhanced.iv)Ingestion of the microbe or cell by the phagocyte-following attachment and then depolymerization of actin filaments send pseudopods out to engulf the microbe and place it in endocytic vesicle called phagosome.V)Destruction of the microbe or cell-Phagocytes contain membranous sacs called lysosome produced by the Golgi apparatus that contain various digestive enzymes. Answer-Opsonization of pathogens by antibody ,complement factors C1q,C3b,and Can,and lectins can assist phagocytic cell in recognition of pathogens and attachment to initiate phagocytosis.However not all pathogen recognition is opsonin dependent.Phagocytes can also recognize molecular structures that are common to many groups of pathogenic microbes.Such structures are called pathogen associated molecular patterns .(PAMPs).Common pamps include the following- i)peptidoglycan,ii)flagellin iii)lps iv)lipopeptides v)nucleic acid. The structures that allow phagocytic cells to detect pamps are called pattern recognition receptors .One group of PRR's is the toll like receptors.which bind to the various pamps and communicate with the nucleus of the phagocyte to elicit a response.Many tlr's are located on the surface of a phagocyte ,but some can also be found embedded in the membranes of interior compartments and organelles.These interior prr's can be useful for binding and recognition of intracellular pathogens that may have gained access to the inside of the cell before phagocytosis could take place .In addition to providing the first step of pathogen recognition ,the interaction between pamps and prrs on macrophages provide an intracellular signal that activates the phagocyte ,causing it to transition from a dormant state of readiness and slow proliferation to a state of hyperactivity ,proliferation,production of cytokines and enhance intracellular killing.PRR's on macrophage also respond to chemical distress signals from damaged or stressed cells.This allows macrophages to extend their responses beyond protection from infectious disease.