Phagocytosis LO Describe phagocytosis as a defence mechanism

Phagocytosis LO: Describe phagocytosis as a defence mechanism. Some Most All • What role do lysosomes have in phagocytosis? • What is “phagocytosis”? • What is the first line of defence against disease?

Today we are covering from the specification: Pages 102 & 103 of your text book

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Artificial immunity 4 of 38 © Boardworks Ltd 2008

What is the first line of defence to disease?

What is the first line of defence to disease? Barriers to entry.

The body’s barriers to entry A protective covering The skin covers the body surface, providing a physical barrier that most pathogens find hard to penetrate. Epithelia covered in mucus Many epithelial layers produce mucus, which acts as a further defence against invasion. In the lungs, pathogens stick to this mucus, which is then transported away by cilia, up the trachea, to be swallowed into the stomach. Hydrochloric acid in the stomach This provides such a low p. H that the enzymes of most pathogens are denatures and therefore the organisms are killed.

The immune response 8 of 38 © Boardworks Ltd 2008

Non-specific immune response The non-specific or innate immune response quickly targets a wide range of pathogens and foreign substances. Phagocytosis, inflammation and the antimicrobial proteins lysozyme and interferons are all part of this immune response. l Lysozyme is an enzyme that disrupts the cell walls of gram-positive bacteria by digesting the peptidoglycan. It is found in human tears, saliva and lysosomes. l Interferons are proteins produced by virus-infected body cells in response to the virus. Interferons trigger the production of a second protein that inhibits viral replication by binding to m. RNA coded by the virus. 9 of 38 © Boardworks Ltd 2008

Specific immune response The specific or adaptive immune response can target a specific pathogen, although it is slower to act than the non-specific response. It features two main types of response to pathogens: l the cellular or cell-mediated response involves highlyspecialized cells that target pathogens inside cells. l the humoral or antibodymediated response targets pathogens in body fluids with antibodies. 10 of 38 © Boardworks Ltd 2008

What is phagocytosis? • Phagocytosis (from Ancient Greek φαγεῖν (phagein) , meaning "to devour", κύτος, (kytos) , meaning " cell", and -osis, meaning "process") is the cellular process of engulfing solid particles by the cell membrane to form an internal phagosome by phagocytes. • It can be used by the immune system as a nonspecific second line of defence against invading pathogens.

What happens during inflammation? 12 of 38 © Boardworks Ltd 2008

Phagocytosis flow chart Phagocytes – originate from bone marrow / foetal liver • Pathogen recognised as foreign – pathogen is antigenic; chemotaxis • Pathogen attached to phagocyte by antibody and surface receptors • Engulfed by phagocyte by endocytosis – invagination of plasma cell membrane to form a phagosome (a membrane bound vesicle containing the pathogen) • Lysosomes (containing lysins & hydrolytic enzymes) fuse to phagosome • Release of H 2 O 2, HCl, free radicals into phagosome • Digest pathogen – harmless products removed (egested / excreted) or used by phagocyte 13 • Phagocyte also displays antigenic components on external surface of plasma cell membrane (antigen presentation) to start immune response

Non-specific immunity: true or false? 14 of 38 © Boardworks Ltd 2008

Phagocytosis flow chart Phagocytes – originate from bone marrow / foetal liver • Pathogen recognised as foreign – pathogen is antigenic; chemotaxis • Pathogen attached to phagocyte by antibody and surface receptors • Engulfed by phagocyte by endocytosis – invagination of plasma cell membrane to form a phagosome (a membrane bound vesicle containing the pathogen) • Lysosomes (containing lysins & hydrolytic enzymes) fuse to phagosome • Release of H 2 O 2, HCl, free radicals into phagosome • Digest pathogen – harmless products removed (egested / excreted) or used by phagocyte • Phagocyte also displays antigenic components on external surface of plasma cell 15 membrane (antigen presentation) to start immune response 15 minutes – Label your diagram of phagocytosis. Summarise and add the extra information to the correct part of the flow diagram.

To Do: 1. Read pages 102 & 103. 2. Add any extra information from the diagram in the book onto your flow diagram. 3. Answer summary questions 1 & 2. 10 minutes

Spot Quiz 1. Are phagocytes an example of specific or nonspecific immunity? 2. What is formed when a phagocyte infolds and engulfs a pathogen? 3. What do lysosomes contain? 4. What is the process called when vesicles bind and release their contents from the cell membrane? 5. What cell organelle manufactures proteins? 6. What cell organelle releases vesicles e. g. lysosomes?