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IgG protect against bacteris, viruses, neutralise bacterial toxins, trigger compliment protein systems and bind antigens to enhance the effectiveness of phagocytosis. Main function of IgA is to bind antigens on microbes before they invade tissues. It aggregates the antigens and keeps them in the secretions so when the secretion is expelled, so is the antigen. IgM enhance ingestions of cells by phagocytosis. In the case of several parasites that infect the gastrointestinal tract, the mechanisms by which Ig, and in particular, IgA, may function are unclear, but it is likely that inhibition of attachment plays a role For example, mucosal anti-Giardia IgA antibodies may prevent infection by inhibiting attachment of the organism to the intestinal epithelium Intestinal IgE antibodies might contribute to the elimination of T.
Finally, antibodies generated against the host receptors themselves can also block infection of a number of different organisms 50 - In the case of viruses, several studies have identified antibodies that inhibit fusion of viral and host membranes or entry into susceptible target cells. For enveloped viruses, antibodies can block an interaction between a viral protein necessary for fusion and its cellular receptor In the case of West Nile virus, a neutralizing monoclonal antibody likely sterically constrains low-pH-mediated rearrangements of E proteins 61 , Similarly, anti-influenza virus HA antibodies can hinder the low pH-induced structural changes necessary for fusion of viral and endosomal membranes 63 , It is possible that anti-influenza HA antibodies can inhibit both attachment and post-attachment steps An interesting twist on fusion inhibition was described for a mAb against influenza virus HA.
The mAb becomes internalized at acid pH through the Fc neonatal receptor FcRn and reduces viral replication following apical exposure of Madin-Darby canine kidney cells to influenza virus. As virus, mAb, and FcRn colocalize within endosomes, it is possible that inhibition of infectivity occurs by interfering with fusion of viral envelope and endosomal membranes Non-enveloped viruses generally enter cells by endocytosis, and escape from the endocytic vesicle is mediated by capsid protein.
Antibodies against polio virus may stabilize the capsid and prevent the structural rearrangements necessary for vesicle escape 29 , 67 , Inhibition of other steps in organism lifecycles A number of studies have revealed the ability of antibodies to inhibit organisms once they have successfully entered cells.
In order for intracellular neutralization to be accomplished, antibodies must be internalized by host cells. Internalization of antibodies can occur as a result of coating of the organism, in which case, the coated organism must be capable of cell entry, or through Fc receptors. In addition, cells have been engineered to express intracellular antibodies intrabodies for potential therapeutic purposes Intracellular neutralization can potentially interrupt an organism's lifecycle by interfering with the release, replication or expression of genomic material.
As an example, adenovirus type 5 antihexon mAb 9C12 allows viral attachment, cell entry and intracellular transport of the virus to the nuclear periphery Nonetheless, 9C12 neutralizes virus infectivity, likely by interfering with capsid uncoating and the release of viral genome A rabbit anti-HPV16 L2 serum was able to neutralize HPV16 pseudoviruses through a mechanism that appeared to involve, at least in part, blocking the transport of viral genome to the nucleus IgA directed against surface proteins or glycoproteins can mediate neutralization of Sendai virus, influenza virus, and measles virus within susceptible target cells 72 - In addition, IgA directed against measles virus M and N proteins, which are internal to the membrane, can inhibit measles virus replication within Vero cells 73 , Similarly, IgA inhibits transcytosis of rotavirus through polarized Caco-2 cells IgA can also introduce a conformational change in the rotavirus VP6 trimer, which is exposed after internalization of virus.
The structural change results in transcriptionally incompetent particles 78 , A novel mechanism of intracellular virus inhibition was described by Mallery, et al.
This mechanism of inhibition would not be expected to work with enveloped virus, since the antibody would be shed along with the envelope prior to internalization within the cytoplasm. An interesting example of intracellular antibody function in a bacterial infection was described by Wang, et al. A mAb against listeriolysin O, the pore-forming toxin of Listeria monocytogenes, blocks L.
Inhibition likely occurs as a result of intracellular neutralization of a secreted Listeria virulence factor With respect to parasites, IgA is reported to inhibit the replication of Toxoplasma gondii in enterocytes In addition, a mouse monoclonal IgG2b antibody, which enters host fibroblasts upon invasion of the antibody-treated organism, inhibits the intracellular growth of T. Inhibition of later steps Antibodies are capable of binding to nascent virus and inhibiting their liberation from infected cells.
This function has been described for antibodies directed against the neuraminidase of influenza A virus It has also been suggested that antibody directed against influenza A virus M2 protein influences the efficiency of virus budding An mAb against rubella virus E1 glycoprotein was reported to delay the release of virus, perhaps by affecting virion assembly 87 Antibody functions dependent on complement Activation of the complement cascade by antibody can result in the lysis of organisms or of infected cells In addition, organisms bound by complement can be internalized by phagocytic cells, with resultant clearance of the organism.
Internalization through complement receptors on antigen-presenting cells can also result in the processing of antigen for presentation to T lymphocytes. The details of complement activation have been reviewed elsewhere It is important to note that antibodies that bind and activate complement may also directly inhibit pathogens in the absence of complement. Complement activation may also have an indirect effect on pathogens by recruiting and activating leukocytes to sites of infection 89 , Similarly, complement-activating antibodies may engage Fc receptors see below.
The Ig subtype and IgG subclass of antibody are major determinants of complement activation For the most part in this review, we limit the discussion to antibodies that affect pathogens in the presence of complement but that in the absence of complement either have no or reduced anti-microbial activity.
A role for IgM and complement in limiting West Nile virus infection in mice has been suggested More recently, Vogt, et al. Antibodies that both neutralize and mediate complement-dependent lysis of influenza virus-infected cells may provide broader strain cross-reactivity than antibodies that only neutralize Furthermore, the addition of complement has long been known to increase the infectivity-inhibiting activity of neutralizing antibodies against several viruses, including influenza viruses 96 , Newcastle disease virus 97 , herpes simplex virus 98 , and Japanese encephalitis virus Paramyxoviruses represent an interesting case in terms of the role of complement, since one study has shown that antibody can neutralize human parainfluenza virus type 2 with little contribution by complement, whereas neutralization of mumps virus and simian virus 5 was dependent on complement In a mouse model of respiratory syncytial virus, passive immunization of a non-neutralizing mAb was shown to protect animals from intranasal challenge.
The mAb lost protective activity as a Fab, and de-complementation of mice reduced the degree of protection Similarly, protective mAbs against Semliki Forest virus lose some effect in complement-depleted mice However, such complement-mediated effects are inhibited by the presence of regulators of complement activation found on infected cells or on the virus itself , Recently, complement-mediated phagocytosis of apoptotic, HIV-1 infected T cells by polyreactive antibodies has been reported Another study has found that antibody from HIVinfected subjects is more potent than that from HIVinfected subjects in complement-mediated inactivation of the respective virus.
Given the multiple potential consequences of complement, either directly or indirectly, its role in HIV infection in vivo remains unsettled - Natural antibodies, generally of the IgM subtype, activate complement and can neutralize influenza virus A unique function of antibody is to initiate the clearance of pathogens via complement activation and binding to erythrocyte complement receptor 1 CR1 ; the result of such binding sequesters the pathogen from invading susceptible tissue and may facilitate the destruction of the organisms by tissue macrophages
Evaluation of Mycograb, amphotericin B, caspofungin, and fluconazole in combination against Cryptococcus neoformans by checkerboard and time-kill methodologies.
It is important to note that antibodies that bind and activate complement may also directly inhibit pathogens in the absence of complement. The most critical incentive for measuring antibody functions is to provide a basis for vaccine development and for the development of therapeutic antibodies.
An mAb against rubella virus E1 glycoprotein was reported to delay the release of virus, perhaps by affecting virion assembly 87 Antibody functions dependent on complement Activation of the complement cascade by antibody can result in the lysis of organisms or of infected cells These adhesins are targets for antibodies that, in a manner somewhat analogous to virus neutralization, can inhibit attachment 32 - A randomized, blinded, multicenter trial of lipid-associated amphotericin B alone versus in combination with an antibody-based inhibitor of heat shock protein 90 in patients with invasive candidiasis.
This is consistent with information indicating that the rate of clearance of antigen by the reticuloendothelial system is greatly increased in the presence of specific antibody ,
It is important to note that antibodies that bind and activate complement may also directly inhibit pathogens in the absence of complement. Nonetheless, 9C12 neutralizes virus infectivity, likely by interfering with capsid uncoating and the release of viral genome
A neutralizing antibody against the E1 glycoprotein of Sinbis virus also induces conformational changes ADCC has also been described for Ehrlichia risticii and Coxiella burnetii-infected cells and for Brucella abortus, though, as with other bacteria, the role, if any, of ADCC in these infection in vivo is unknown - Internalization of antibodies can occur as a result of coating of the organism, in which case, the coated organism must be capable of cell entry, or through Fc receptors. Antibody-mediated complement lysis of Legionella pneumophila is ineffective; however, organisms opsonized with both antibody and complement are phagocytosed by PMNs, although killing of ingested bacteria is limited This function has been described for antibodies directed against the neuraminidase of influenza A virus More recently, Gorander, et al.
Fc receptor but not complement binding is important in antibody protection against HIV. Neutralization of infectivity In vitro, antibodies are capable of blocking the infectivity or pathogenesis of viruses, bacteria, parasites, and fungi. More recently, Vogt, et al.
It is possible that anti-influenza HA antibodies can inhibit both attachment and post-attachment steps Examples of antibody functions include neutralization of infectivity, phagocytosis, antibody-dependent cellular cytotoxicity ADCC , and complement-mediated lysis of pathogens or of infected cells. Hope T. Ncea level 3 english essay writing lyric essay ucla address confirmation saints essay basketball vs soccer comparison essay us senate begins gun control debate essay research paper on exhaust gas circulation pdf editor a clockwork orange critical analysis essay. A rabbit anti-HPV16 L2 serum was able to neutralize HPV16 pseudoviruses through a mechanism that appeared to involve, at least in part, blocking the transport of viral genome to the nucleus