1、Lecture 6BIOL 5331Phagocytosis and the Interactionsof Various PhagocytesBIOL 533Lecture 6Medical MicrobiologyLecture 6BIOL 5332Leukocyte Chemotaxins Types of chemotaxins C5a attracts neutrophils and monocytes Made by bacteria Peptide clipped off N-terminus(beginning with N-formylmethionine)during pe
2、ptide maturation after protein synthesis Made by bacteria and nucleated blood cells Leucotrieneslipid products of cell membrane metabolismLecture 6BIOL 5333Leukocyte Chemotaxins Function of chemotaxins Enhance and direct motility of phagocytic cells To a limited extent,oxidative metabolism of phagoc
3、ytic cellsLecture 6BIOL 5334Opsonization and Opsonins General aspects Substances that enhance ability of phagocytes to ingest microbes Defend against presence of capsules and other microbial mechanisms that interfere with phagocytosisLecture 6BIOL 5335Opsonization and Opsonins Types of opsonins Anti
4、bodies C3b component of complement Binds covalently to bacterial surface and is recognized by receptors on neutrophils,monocytes,and macrophage Bacteria become bound to surface of phagocyte facilitating their uptakeLecture 6BIOL 5336Opsonization and Opsonins Types of opsonins,continued Mechanism Whi
5、te blood cell receptors for C3b At least 3CR1,CR2,CR3(complement receptor)Children deficient in CR3 very vulnerable to bacterial infectionsLecture 6BIOL 5337PhagocytesTypes of Cells Neutrophilscell origin Actively motile cells produced in bone marrow Differentiate from stem cells over about a two-we
6、ek period Production of granules during this time Azurophil Produce specific granules laterLecture 6BIOL 5338PhagocytesTypes of Cells Neutrophilscell origin,continued Upon maturation(in numbers of 1010 per day),they move into peripheral blood and circulate for about 6.5 hours Next move into capillar
7、y bed and marginateLecture 6BIOL 5339PhagocytesTypes of Cells Neutrophilscell origin,continued Margination caused by stickiness due to interleukin-1 Summoned by chemotaxis,they move through endothelial cell junctions(diapdesis)into extravascular tissue spacesLecture 6BIOL 53310PhagocytesTypes of Cel
8、ls Neutrophils are most active in gut Gut has enormous microbial population lying just one cell layer away from aseptic tissue Flora generates large amounts of chemotaxins that recruit most of bodys available leukocytesLecture 6BIOL 53311PhagocytesTypes of Cells As a result,submucosa of gut is in a
9、constant state of inflammation Keep microbial flora down Synthesis of neutrophils inhibited by chemicals or radiation Infections in gut regionLecture 6BIOL 53312PhagocytesTypes of Cells Monocytes and macrophage Compared to neutrophils Arrive at damaged tissue later in infection Days after neutrophil
10、s have been active in fighting intruders Eventually settle in tissues and become resident macrophageLecture 6BIOL 53313PhagocytesTypes of Cells Monocytes and macrophage Share progenitor cell type,but kinetics of maturation&appearance are very different Monocytes continue cell differentiation after l
11、eaving bone marrow Monocytes and macrophage involved in both constititive and inducible mechanisms Interact with T cells and play important role in cell-mediated immunityLecture 6BIOL 53314PhagocytesTypes of Cells Tissue(resident)macrophage Exist throughout body Different names and functions in diff
12、erent tissues Kupffer cellsliver Alveolar macrophagelungs Osteoclastsbone MicrogliabrainLecture 6BIOL 53315PhagocytesTypes of Cells Monocyte and macrophage functions Phagocytize invading microbes Contribute greatly to inflammatory response Releases IL-1enhances sticking of neutrophil to capillary en
13、dothelia TNFactivates newly arrived neutrophilsLecture 6BIOL 53316Mechanism of Phagocyte Killing Neutrophils General steps Attach to microbes Ingest microbes Kill microbes Granulesconsidered as enlarged lysosomes containing hydrolytic enzymesLecture 6BIOL 53317Mechanism of Phagocyte Killing Neutroph
14、il granule types Azurophil(primary granule)Contains Lysozyme Elastase A chymotryptic-like protease Myeloperoxidase Several antibacterial cationic proteinsLecture 6BIOL 53318Mechanism of Phagocyte Killing Neutrophil granule types Specific(secondary granule)Contains Cytochrome Lysozyme Lactoferin(iron
15、-binding protein)Vitamin B12 binding protein CollagenaseLecture 6BIOL 53319Mechanism of Phagocyte Killing The neutrophil membrane Contains receptors for chemotaxin and opsonins After binding chemotaxins,receptors are internalized and replaced with new onesLecture 6BIOL 53320Mechanism of Phagocyte Ki
16、lling Effectiveness of chemotaxis:very effective Neutrophils are very motile Move by rearranging cytoplasmic microfilaments and microtubules Actin and myosin in microfilaments are affected by protein gelsolin Portions that face upstream in chemotactic gradient form structure called lamellipodium Cyt
17、oplasm is densely packed with microfilaments Portions face downstream form knob-like uropodLecture 6BIOL 53321Mechanism of Phagocyte Killing Process of phagocytosis General aspects Differs from pinocytosis in that particles,not liquids,taken upLecture 6BIOL 53322Mechanism of Phagocyte Killing Proces
18、s of phagocytosis,continued Receptors on phagocyte surface progressively attach to ligands on bacterial surface Stimulates mechanisms of killing Oxidative metabolism leading to production of hydrogen peroxide and compounds lethal to microbes(oxygen-dependent killing)Discharge of toxic compounds from
19、 granules into phagosome(oxygen-independent killing)Lecture 6BIOL 53323Mechanism of Phagocyte Killing Process of phagocytosis,continued Form phagosomepouch-like structure that invaginates,displacing the nucleus and granules toward uropod Form phagolysosomemembrane of granules and phagosome fuse,rele
20、asing toxic substances Forms separate pinched-off organelle Bacteria coated with antibacterial proteinsLecture 6BIOL 53324Oxygen-Dependent Killing Fusion of specific granules with phagosome membrane(derived from plasma membrane)brings together:NADPH oxidase(oxidizes NADPH;found in neutrophil plasma
21、membrane)Unique cyt b(granule membrane)A quinoneLecture 6BIOL 53325Oxygen-Dependent Killing Reaction O2 O2(reduces oxygen to superoxide radical)2O2 +H2O H2O2+O2(superoxide dismutase)Lecture 6BIOL 53326Oxygen-Dependent Killing Patients lacking cytochrome components Children having chronic granulomato
22、us disease(CGD)Failure to synthesize superoxide radical and therefore hydrogen peroxide Due to decreased amount of cytochrome b Gene for larger subunit is missing(90K,20K)Lecture 6BIOL 53327Oxygen-Dependent Killing Children having chronic CGD,contd.Neutrophils can phagocytize normally,but do not eff
23、iciently oxidize NADPH and kill via oxidative pathway Usually dont survive into adulthoodLecture 6BIOL 53328Oxygen-Dependent Killing How does oxidative process kill?Interaction with myeloperoxidase supplied by fusion with azurophil Combines chloride ions and hydrogen peroxide to form hypochlorous io
24、ns(analogous to bleach)Bacteria lacking catalase produce hydrogen peroxide(pneumococci);basically commit suicide Pneumococci are not dangerous to CGD patientsLecture 6BIOL 53329Oxygen-Independent Killing Process Triggered by binding opsonized bacteria to the plasma membrane of neutrophils Specific g
25、ranules fuse first Deliver several bacteriodical proteins,including lysozyme and lactoferinLecture 6BIOL 53330Oxygen-Independent Killing Azurophil granules discharge antimicrobial cationic proteins Some are amphipathic and resemble other cationic surface proteins such as polymyxin BLecture 6BIOL 533
26、31Oxygen-Independent Killing Azurophil granules,continued Disrupt outer membrane of Gram and kill by causing leakage of vital components Each of the proteins has unique antimicrobial spectrum,but tend to affect Gram more than Gram+Proteins may account for survival of some CGD childrenLecture 6BIOL 5
27、3332Oxygen-Independent Killing Efficiency Bacterial killing under highly anaerobic conditions of deep abscesses Patients lacking genes Coding for cationic proteins None found,maybe lethalLecture 6BIOL 53333Oxygen-Independent Killing Chediak-Higashi syndrome(genetic disease)Premature fusion of neutro
28、phil granules while cells in bone marrow When mature cells phagocytize,granules are already spent,substantially reducing killing powerLecture 6BIOL 53334Comparison of Bacterial Sensitivity Gram rods in gut killed by oxygen-independent Gram+bacteria on skin and upper respiratory epithelia are resista
29、nt to oxygen-independent and killed by oxygen-dependentLecture 6BIOL 53335Mechanism of Phagocyte Killing Eosinophils Much like neutrophils,but indicative of parasitic infectionLecture 6BIOL 53336Killing by Monocytes and Macrophage General aspects Tend to take care of what is left after battle with n
30、eutrophils Mechanisms of chemotaxis,phagocytosis,and killing resemble mechanisms of neutrophils Not studied in same detailLecture 6BIOL 53337Killing by Monocytes and Macrophage Differences Continue to differentiate after leaving bone marrow and are activated Called“angry macrophage”Phagocytize more
31、vigorously Take up more oxygen Secrete large quantity of hydrolytic enzymes In general,better prepared to killLecture 6BIOL 53338Killing by Monocytes and Macrophage Activated by Elicited by substances made in response to presence of bacteria(C3b)or viruses(interferon)Endotoxin of Gram Tetrapeptide d
32、erived from immunoglobulins(tuftsin)Lecture 6BIOL 53339Killing by Monocytes and Macrophage Microbial(bacterial,fungi,protozoa)growth within Some can grow until activated,then killed Participation in immune response Help rid body of not only microbial invaders,but also tumor and foreign cellsLecture
33、6BIOL 53340Killing by Monocytes and Macrophage Immune response process Stimulate development of T lymphocytes Respond to signals from other lymphocytes that stimulate differentiation and activation of macrophageLecture 6BIOL 53341Phagocytotic Killing Macrophages/neutrophils/mast cells stimulated by
34、TNF interferon Produce reactive nitrogen intermediates Nitric oxide Nitrite(NO2)Nitrate(NO3)Lecture 6BIOL 53342Phagocytotic Killing Released from cells or contained within vacuoles Macrophages produce NO from arginine when stimulated by cytokines NO can block cellular respiration by complexing iron in electron transport proteinsLecture 6BIOL 53343Macrophage KillingHerpes simplexToxoplasma gondiiLeishmania majorCryptococcus neoformansSchistosoma mansoniLecture 6BIOL 53344Lecture 6 Questions?Comments?Assignments.
