The Listeria monocytogenes Essay


Definition of Innate Immune system and its importance to support human organic structure against intracellular encroachers. Be every bit concise as possible, because a good essay focal points on the inquiry, and does n’t rewrite the text books. You will necessitate to explicate the map of the cells ( dendritic and macroph ) .

Definition of Microbial Virulence and its importance to happen disease or infection in human organic structure. Again, focal point on L.monocytogenes and its virulency factors, such as listeriolysin and internalin, and of import mechanisms such as lysosomal flight and how cells are infected ( listeriopods ) . Who gets disease… ..

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The purpose of this essay is to see the map of Macrophage and Dendritic cells how they could play critical function to command and defence human organic structure as initial immune system. Have you found any documents yet? Most are mouse theoretical accounts, so you need to demo that you are cognizant that they are a via media to the existent state of affairs ( infection by nutrient ) whereas mouse theoretical accounts are endovenous, infected theoretical accounts.

The purpose of this essay is to exemplify L.monocytogenes ‘s virulency as a tool for get awaying from Macrophage cells and Dendritic cells. And any differences between these cells in how they handle l.monocytogenes ( that ‘s really the of import portion ) .

Describe the function dendritic cells and macrophage cells play in the control and flight of Listeria monocytogenes.


The intent of this essay is to exemplify Listeria monocytogenes ‘s virulency as a tool for get awaying from phagosome vacuole of Macrophage and Dendritic cells. The parametric quantities of this essay will be exemplifying instead than being deep probe. In other word, from the inquiries that will be answered subsequently, how do L.monocytogene go opposition or have the ability to get away from phagosome before merger with lysosome vacuole? Another inquiry is that what makes L.monocytogene virulency? First, the relationship between Dendritic and Macrophage will be explained. Second, this essay will seek profoundly inside the contents of cell to detect what the differences between these antigenic presenting cells in relation to response to infection of L.monocytogene as intracellular encroacher? Third, some manner of action of virulency factors of L.monocytogene will be mentioned. Last but surely non least, some suggestions for commanding of L.monocytogene get awaying will be given.

Glance of innate immune system

The immune system plays a critical function to protect human organic structure from spread out L.monocytogenes into neighbouring cells or variety meats ( Zenewicz, L.A, 2007 ) . Innate immune cells consist of different cells with regard to map and form. There are two immune cells play of import defense mechanism against any invader source straight. These cells are dendritic cell and macrophage cell. A macrophage cell, which is found in tissues and variety meats e.g. lung and encephalon, is derived originally from monocyte, which is found in blood watercourse. Dendritic cell can be found in, as good, in many variety meats. It plays of import functions in unconditioned unsusceptibility to extinguish bugs every bit good as, macrophages. All of these two cells called Antigenic Presenting Cells ( APC ) due to show microbic merchandises after phagocytic mechanism and degrading bug ‘s protein into peptides, and show peptides on Major Histocompatibility Complex ( MHC I, II ) ‘for acknowledgment by the T cells ‘ ( Abbas, et Al, 2007: p.116 ) .

However, there are many micro-organisms have adapted themselves in order to occupy human organic structure and occur infective disease through intracellular infective mechanism by virulency factors which might be toxin secernments and many factors. Virulence factors can invert the balance of conflict between bacteriums and APCs for bacterium. One of those intracellular bugs, which is interested by this essay, is Listeria monocytogenes. This bacteria is a Gram-positive rod and it causes Listeriosis in worlds and animate beings, in add-on, the infection by this bacteria is perchance by “ hypodermic vaccination and eating ” ( Liu. D, 2008: p.99 ) .

Intracellular immune reaction of L. monocytogenes

Phagocytosis mechanism

Any of these cells within APCs has the ability to steep foreign organic structure to its cytol surrounded by vacuole which is really of import to maintain the bug from get awaying into cytol. The Phagocytosis procedure has been explained by Abbas, et Al, ( 2007: p.11 ) in inside informations by following stairss. The first measure, bugs are recognised in surface of APCs by many receptors e.g. scavenger, mannose and Toll-like receptors. The following measure, APCs membrane ‘zips up about bug ‘ and steep it in vacuole. This vacuole could be divided into two vacuoles sing phagosome development in PH degrees and GTPase. Lastly measure, the early endosome and late endosome, which is more acidosis than the first one to put for merger with lysosome, harmonizing to Shaughnessy, et Al, 2007. These GTPase are Rab5a ( early ) and Rab7 ( late ) . It has been demonstrated by Shaughnessy, et Al, ( 2007 ) and Abbas, et Al, ( 2007: p.35 ) that Rab5a is important for subsequent procedure to fusion lysosome with phagosome vacuole in order to kill bug by reactive O species ( ROS ) and nitrogen intermediates ( azotic oxide NO ) and proteolytic enzymes such as oxidase. Therefore, in instance of steeping L.monocytogenes, that GTPase go involve in ( Myers, et Al, 2000 ) .

The job is L.monocytogenes has been demonstrated to avoid late endosome and lysosome ; besides it has been found that in its early vacuole in macrophages has non possessed Rab5a. Thus, excluded Rab5a could disrupt phagosomal ripening ( Shaughnessy, et Al, 2007 ) .

Dendritic & A ; Macrophage cells correlativity

The most one possible importance different between DCs and macrophages is that DCs play an of import function in adaptative unsusceptibility to extinguish viruses and tumour cells. In contrast, one of import similarity between them, the effecter cells ( Naive T CD4+ cells ) are stimulated and activated by DCs and macrophage with IL-12, IL-1 that leads to activation macrophage by those effector cells to kill the phagocytic bug ( adaptative unsusceptibility ) . Furthermore, IFN- ? is secreted by certain cells e.g. Natural Killer cell ( NK ) that contact with intracellular pathogens straight or by acknowledging MHC I molecules in non-phagocytic septic cells. Therefore, that action leads to let go of IFN- ? ( Champoux, et Al, 2004: p.121 and Abbas, et Al, 2007: p.117 and Shaughnessy, et Al, 2007 ) .

Macrophage cells could be indirectly activated to kill the phagocytic bug by other non-phagocyte cells. The fact that is DCs the merely 1 cell in immune system has two distinct complex categories MHC I, II molecules. In add-on, it has the ability to phagocyte bugs and show their merchandises attach with these categories. Therefore, T cells CD8+ ( Cytotoxic ) can be stimulated by DCs via TCR binds to MHC I molecule. That action allows CD8+ cells to bring forth TNF and IFN- ? . This IFN- ? can trip macrophages to go listericidal activity to kill micro-organisms by merger phagosome with lysosome vacuole ( Abbas, et Al, 2007: p.294 ) . In add-on, TNF-a, which considers the importance factor in opposition to enteric L.monocytogenes, is produced and “ mediated growing control ” when the flagellin of it attaches with Toll-like receptor-5 ( TLR5 ) in DCs and other cells ( Dons, L. , et Al, 2004 ) .

Furthermore, CTLs bind straight with non-phagocytic line of descent cells, which has been infected by L.monocytogenes, with MHC I that has the cytosolic antigens of listeria merchandises when L.monocytogenes escaped from phagosome to the cytol. These merchandises are lysed by proteasome into antigenic antigenic determinants. As a consequence of staying CTLs with non-phagocytic line of descent cells, lysing septic cells through perforin and granzymes ( apoptotic ) that leads to L.monocytogenes becomes extracellular for a minute that could let the macrophages to capture it, harmonizing to Zenewicz, L.A, et Al, ( 2007 ) and Liu. D. ( 2008: p.432-435 ) .

Therefore, macrophages perchance kill L.monocytogenes by two ways. The first manner is by CTLs when it destroys non-phagocyte septic cells by acknowledging MHC I molecule. The 2nd manner is by NK cells that act the same as CTLs or kill L.monocytogenes, when it becomes extracellular, and let go of Interferon gamma as indispensable interferon for clearance intracellular pathogen. However, the correlativity of DCs and macrophage could be indirectly for clearance L.monocytogenes via CTLs.

Dendritic cells

DCs are critical cells to link between innate and adaptative unsusceptibility ( Zenewicz, L.A, et Al, 2007 ) . In add-on, DCs play important map in the first and ordinance of immune responses. DCs are able to phagocyte bugs even intracellular bacteriums e.g. L.monocytogenes and septic cells and so there are many stairss could make. One of them, mobilisation and migration into lymph node to show those foreign antigens on its surface with MHC II for helping recognise T-helper cells CD4+ to distinguish ( Paschen, et Al, 2000 ) . DCs are activated by signalling cascade of TLRs consequence in merchandise of specific acknowledgment of pathogen Zenewicz, L.A, et Al, 2007 ) .

The opsonization of L.monocytogenes by DCs through interceding Fc receptor may depend on human Ig ‘s ( Antibodies ) for L.monocytogenes antigens ( Kolb-M & A ; auml ; urer, A. , et Al, 2003 ) . It has been suggested by Kolb-M & A ; auml ; urer, A. , et Al, ( 2003 ) that some DCs unable to kill L.monocytogenes in phagosome vacuole effect of a distinguishable bacterial violent death volume of their phagosome vacuoles.

It has been reported by Paschen, A. , et Al, ( 2000 ) many intracellular bacteriums such as L.monocytogenes ‘inhibit CD4+ T cell responses ‘ by intervention with bring oning antigen specific hostility in murine APC MHC II.

As Paschen, A. , et Al, ( 2000 ) says mature DCs has lost the efficiency of capturing listeria ( Phagocytosis ) , nevertheless, immature DCs has the ability to phagocyte L.monocytogenes that escapes in short clip from phagosome vacuole and that leads to morphological alterations of DCs to show listeria antigens for CD4+ T cells. Furthermore, the information has non been shown that mature DCs have high degree of look MHC II without intracellular listeria, nevertheless, immature DCs have low degree of look MHC II adhering with antigen ( Kolb-M & A ; auml ; urer, A. , et Al, 2003 and Paschen, et Al, 2000 ) .

However, it has been observed by Paschen. A. , et Al, ( 2000 ) that human DCs have the efficiency against ‘cytolytic activity of listeriolysin ‘ .

Inflammatory Cytokines

As can be seen from the map of IFN- ? , considers the most of import cytokine for clearance L.monocytogenes. This bacteria benefits from initiation of type I interferons, which is really of import for clearance viral infection, to heighten its growing and get awaying into cytosol ( Zenwicz, L.A. , et Al, 2007 ) . Harmonizing to Zenwicz, L.A. , et Al, ( 2007 ) this interferon to be induced by listeria acknowledgment tract is independent to many receptors, for illustration, Toll-like receptor 2,4 and receptor interaction protein 2 ( RIP-2 ) , in contrast, it depend on ‘the written text factor IFN regulative factor 3 ( IRF3 ) and serine-threonine kinase TNFR-associated NF-kB kinase ( TANK ) -binding kinase 1 ( TBK1 ) .

Listeria monocytogenes


As mentioned before the manner of entry tract for this bug is likely two ways. The first is direct tract via enterocytes invasion surfacing microvilli absorbent epithelial tissue by specific receptor reaction which has been thought by Liu, D, ( 2008: p.100 ) that would go on merely in enteric host cells e.g. worlds or guinea hogs, that express listeria encroacher ‘susceptible ‘ receptors isoform. The 2nd tract is by Intestinal translocation mechanism. Therefore, L.monocytogenes spreads out into spleen and liver from mesenteric lymph nodes distribution and makes hepatitis and splenitis ( Liu, D. , 2008: p.100 ) .

This bug is able to be engulfed by DCs, macrophages and M cells etc which is located in Peyer ‘s spots. By specific surface protein in L.monocytogenes called internalin, this intracellular bacteria encourage epithelial cell for invasion ( Champoux, J. J. , et Al, 2004: p.303 ) . Once this bacteria becomes engulfed, its virulency factors assist it to get away from phagosome vacuole. These virulency factors will be discussed subsequently.

Surprisingly, L.monocytogenes besides could last with high virulency in the protozoon Acanthamoeba by miming the same as pathogenesis in APCs ( Zhou, X. , et Al, 2007 ) .

Virulence factors

Listeriolysin O ( LLO )

L.monocytogenes releases cholesterol-dependent cytolysin ( CDC ) , listeriolysin O ( LLO ) which is important for L.monocytogenes virulency. In add-on, this factor is considered the responsible enzyme for L.monocytogenes get awaying to cytoplasm by lysing phagosome vacuole before merger with lysosome vacuole to go phagolysosome vacuole besides it is RBCs hemolysin ( Shaughnessy, L. M. , et Al, 2007 and Liu, D. , 2008: p.108 ) . Gamma-interferon-inducible lysosomal thiol reductase ( GILT ) is the cardinal factor to trip LLO ( Singh, R. , et Al, 2008 ) . Therefore, it has been observed by Singh, R. , et Al, ( 2008 ) that L.monocytogenes LLO becomes active to formation Hales on phagocytic vacuole membrane when active GILT is present. In add-on, in instance of absence the LLO, harmonizing to Henry, R. , et Al, ( 2006 ) the destiny of escaping is fail.

IFN- & A ; szlig ; can be secreted in response to L.monocytogenes infection ; in contrast, it could be considered one of the factors that raise the ability of LLO to be more expeditiously. It has besides been suggested that that INF- & A ; szlig ; heighten the phagosomal vacuole sourness to be more acidic, by phagosomal membrane, to trip LLO ( Zwaferink, H. , et Al, 2009 ) .

It has been stated by Liu. D. ( 2008: p.109 ) and Henry, R. , et Al, ( 2006 ) that LLO becomes active between PH 5.5-6.0. As Henry, R. , et Al, ( 2006 ) demonstrate listeriolysin O could be inactivated by deficient of Rab5a ( GTPase ) that is indispensable for early endosome vacuole in APCs. Thus, the escaping might be prevented. However, it has been discovered that L.monocytogenes does non impact ‘Rab5 exchange ‘ ( Henry, R. , et Al, 2006 ) . The optimal active of LLO obtains in the late endosome of which by Rab7-positive could assist get awaying L.monocytogenes ( Henry, R. , et Al, 2006 ) .

However, there is a cistron where found in L.monocytogenes is considered the chief responsible for get awaying this bacteria from cytosolic vacuoles it is called hly cistron for listeriolysin O ( Zhou, X. , et Al, 2007 ) . Therefore, it has been mentioned that cistron speeds up ‘fusion with early endosomes ‘ and postpones ‘fusion with lysosomes ‘ ( Henry, R. , et Al, 2006 ) .

Actin filament polymerisation ( Actin-based motility )

When L.monocytogenes escape from phagocytic vacuole leads to formation of actin fibrils as covering and environing the bacteria and becomes agreement to organize large “ tail ” ( Tilney, L. G. , et Al, 1989 and Liu, D. , 2008: p.113 ) . This tail fibril becomes at one pole, and helps L.monocytogenes to get away from APCs cytol to another cell cytol ( Liu, D. , 2008: p.113 ) . By that manner, L.monocytogenes could infect other cells by leaping from infected macrophage to another integral macrophage. This procedure would first, be motion intracellular bacteria to the host cell surface, and so distribute out by organizing “ pseudopodal projection or big microvillus ” ( Tilney, L. G. , et Al, 1989 ) .

Flagellin is the indispensable constituent of flagellar fibril ( Dons, L. , et Al, 2004 ) . It has been suggested by Dons, L. , et Al, ( 2004 ) that consists of flagellar fibril may respond like “ adhesions and intercede the binding to ” targeted cell.

However, pseudopodal membrane and the phagocytic vacuole membrane of another APC is perchance dissolved ( Tilney, L. G. , et Al, 1989 ) .

There is a protein called ActA which is a “ surface protein ” capable of polymerising actin and spread of bacteria, therefore, it considers as sufficient protein to modulate actin fibril on bacteria surface to travel send oning fast ( Liu, D. , 2008: p.113 ) .

Phosphoinositde-specific phospholipase C ( PI-PLC )

Broad-range phospholipase ( PC-PLC )


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