The human immunodeficiency virus is a dual isolated RNA virus belonging to the lentivirus genus and the Retroviridae household. The separating feature of HIV is that the mirid bug of the virus contains two indistinguishable individual RNA strands. Upon entry of the mark cell the single-stranded RNA is rearward transcribed by the viral RNA-dependent DNA polymerase, besides referred to as the contrary transcriptase1. Two distinguishable sub-types of HIV, HIV-1 and HIV-2, are identified based on their debut into human population every bit good as by their differential virulency to worlds. The HIV type 1, HIV-1, is the descendant of Pan troglodytes derived Siminan Immunodeficiency Virus ( SIVcpz ) , and it is the more virulent of the two signifier of HIV. HIV-1 histories for the bulk of infections worldwide ( x, ten ) . The HIV type 2, HIV-2, is a descendant of SIV isolated from coal-black mangabey monkeys ( SIVx ) , and is by and large found in countries of West Africa. HIV-2 is less deadly and less catching compared to HIV-1 ( x ) . HIV-2 was besides distinguished from HIV-1 based on the longer clinical latency period and lower rate of morbidity of the resulting disease. Nevertheless, infection by either HIV-1 or HIV-2 finally leads to the development of AIDS in worlds.
The HIV-1 infection procedure begins with the binding of the viral envelope surface protein gp120 to the CD4 receptor on the mark cell ( Fig. 1.1 ) . Once this binding occurs, the gp120 glycoprotein undergoes a series of conformational alterations required for adhering to a chemokine receptor, termed co-receptor 2. Different strains of HIV-1 are classified based upon their use of the chemokine co-receptor: the T-cell-tropic viruses use the CXCR4 chemokine receptor and are referred to as X4 viruses 3 while the macrophage-tropic viruses use the CCR5 chemokine receptor and are referred to as R5 viruses 3, 4-5. Strains of HIV-1 that can use both types of chemokine co-receptors are referred to as dual-tropic viruses. It is by and large believed that HIV-1 transmittals in worlds are initiated with the infection by the macrophage-tropic HIV-1 strains and during progressive infection, the virus displacements toward deriving T-cell tropism. This displacement in viral tropism normally occurs late in the class of disease and marks an accelerated stage in the clinical disease patterned advance ( x ) . Once the gp120-CD4 composite is bound to the appropriate co-receptor, extra conformational alterations expose the transmembrane protein gp41 that gets inserted into the membrane of the mark cell for subsequent merger of the viral and mark cell membranes ( Fig. 1.1 ) . One effect of HIV infection is the diminution in the Numberss of entire and different memory subsets of CD4+ T cells and when the diminution reaches below a critical degree, HIV infected persons develop susceptibleness to timeserving infections that finally culminate into the acquired immunodeficiency syndrome ( AIDS ) . In 2007, there were an estimated 33.2 million instances of HIV infection worldwide with unwritten and venereal mucosal infections accounting for the bulk of all reported instances of HIV-1 infection and transmittal 6.
Fig. 1.1: Cartoon stand foring the procedure of HIV-1 entry into human cells: The surface envelope glycoprotein gp120 of the virus binds to the CD4 receptor on the host cell membrane ensuing in a conformational alteration in gp120 ( a ) that enables co-receptor binding ( B ) followed by the exposure of the gp41 transmembrane glycoprotein ( degree Celsius ) for merger of the viral and cell membranes ( vitamin D ) .
Beginning: Doranz et Al. ( ten ) .
The Macaca mulatta macaque ( Macaca mulatta ) theoretical account is widely used to extensively analyze HIV transmittal. This theoretical account uses either the simian immunodeficiency virus ( SIV ) , a archpriest lentivirus closely related to HIV, or a laboratory-created intercrossed virus called simian-human immunodeficiency virus ( SHIV ) dwelling of cistrons that encode the HIV envelope and the SIV nucleus. Both of these viruses can be easy transmitted to macaques by vaginal vaccination and do AIDS-like unwellness characterized by terrible loss of CD4+ T cells and timeserving infections. This theoretical account of SIV/SHIV infection of macaques is similar to that of HIV in worlds in that the mark cells, physiology, and immunology of the venereal piece of land are comparable. Using this theoretical account, Miller et. Al described the extension and airing of SIV after vaginal transmission7 ( Fig. 1.2 ) . Their survey showed that between yearss 1-4 post-infection merely a few septic cells could be found in the vaginal tissue, the original site of vaccination, every bit good as at distant gut-associated lymphoid tissues ( GALT ) . However, beyond twenty-four hours 4 post-infection, there is a significant addition in septic cells at the local vaginal tissue and a coincident addition over yearss 10-14 at the GALT. These observations correlate good with later studies depicting mucosal SIV infection in Macaca mulatta macaques and HIV infection in worlds ensuing in a rapid depletion of enteric CD4+ T cells by twenty-four hours 14 post-exposure. This utmost degree of depletion of CD4+ T cells occurs chiefly in the mucosal tissues of the gastrointestinal ( GI ) piece of land where more than 60 % of T lymphocytes reside 8-12. It is ill-defined how the virus efficaciously manipulates the mucosal microenvironment taking to the systemic spread of infection since the function the mucosal epithelial tissue plays in feeling HIV infection, triping immune activation, and advancing HIV spread and elaboration remains unknown. A better apprehension of the elaborate stairss during the mucosal infection procedure should supply a model for understanding the extension, airing, and constitution of infection during the acute phase of infection.
Fig. 1.2: Model of delayed systemic SIV reproduction. Survey from Miller et Al. demoing that between yearss 1-4 post-infection merely a few septic cells could be found in the vaginal tissue, the original site of vaccination, every bit good as at distant lymphoid tissues. However, beyond twenty-four hours 4 post-infection, there is a significant addition in septic cells at the local vaginal tissue and a coincident addition over yearss 10-14 at the distant lymphoid tissues.
Beginning: Miller et Al. ( ref ) The Mucosal Microenvironment
About 30-40 % of all new HIV instances occur in adult females through vaginal intercourse, a path that carries the lowest HIV transmittal chance per exposure proposing that the venereal epithelial tissue fails to function as a major barrier against HIV entry. For successful virus transmittal, HIV must be efficient in inventing schemes to traverse the mucosal barrier of the venereal piece of land to infect CD4+T cells. Since unwritten and venereal mucosal epithelial cells express low to negligible degrees of the receptors for HIV, in peculiar CD4, the virus has to use unconventional mechanisms to traverse primary venereal epithelial cell beds. Surveies in the Macaca mulatta macaque theoretical account with SIV suggested that the initial marks of infection may be Langerhans Cells ( LCs ) , subepithelial T-cells and dendritic cells ( DCs ) ( x, ten, ten, ten, ten ) . In order for the virus to make these marks it must successfully perforate the epithelial barrier. There are several proposed mechanisms for how HIV-1 may traverse the mucosal epithelial tissue ( Fig. 1.3 ) . The susceptibleness of epithelial cells to HIV infection is controversial with some surveies reporting that different epithelial cell lines can be fruitfully infected and reassign virus to gut-associated epithelial cells based on the look of certain glycosphingolipids such as galactosylceramide ( GalCer ) . Other surveies have suggested that venereal epithelial cells can adhere, conveyance, seaport, and transmit virus to extra marks, but can non be fruitfully infected ( x, ten, ten ) 13-17. A 2nd proposed mechanism for viral entry across the mucosal epithelial tissue is by transmigration of septic cells through the mucosal epithelial cells. These cells can include septic CD4+ T cells and monocytes found in seeds ( ten, x ) . Langerhans cells ( LC ) constitute another vehicle by which virus may track the mucosal epithelial tissue because it has been shown that LC can try the infinite beyond the mucosal barrier for foreign antigens. Since LC express CD4, CCR5, and CXCR4 and can be found within the venereal piece of land it has been suggested that LC at these mucosal sites can capture HIV and migrate to the run outing lymph nodes where the virus is transmitted to CD4+ T cells, the chief marks of HIV reproduction and airing 21-22. Whether or non the LC become infected after exposure to virus vaccination is still controversial. Some surveies of vaginal mucosal transmittal of SIV in Macaca mulatta macaques demonstrated that submucosal LCs quickly became septic after virus vaccination while other surveies suggest that the CD4+ T cells are the cells infected and that they are the major beginning of infective virus during the acute phases of infection. Ex vivo surveies have demonstrated that LCs are non required for, but may help in, viral transmittal ( x ) . A 4th mechanism by which HIV can be transmitted across the mucosal epithelial tissue is through breaches in the epithelial bed. These breaches can happen as a consequence of injury associated with sexual intercourse or as a consequence of infection with other sexually transmitted diseases that can compromise the strength of the mucosal barrier ( x, ten ) . These interruptions in the epithelial barrier allow the virus entree to susceptible marks of infection in the implicit in tissues but surveies in the Macaca mulatta macaque theoretical account have revealed that barrier break is non necessary for successfully viral transmittal ( x ) . The fifth proposed mechanism by which HIV can be transmitted across the mucosal epithelial tissue is by transcytosis / endocytosis through the mucosal epithelial tissue affecting interactions with cell surface Lipo-Hepin sulphate medieties, enabling infection of the nearby dendritic cells ( DC ) and CD4+ T cells 17-20. This tract was ab initio proposed after virus was observed being transported into endosome like compartments after coming into contact with the surface of epithelial cells ( ten ) . Ex vivo surveies utilizing the cervical explants theoretical account have besides shown that HIV-1 virions can be found in endocytic compartments every bit good as in the cytosol of epithelial cells ( ten ) . Elimination of Lipo-Hepin sulphate medieties was non shown to abrogate viral transcytosis proposing that other host cell factors may besides be involved in viral transcytosis in epithelial cells ( ten ) . Several recent studies ( refs ) have demonstrated a specific interaction of HIV with epithelial cells through the binding of the HIV surface envelope protein gp120 to the cell surface salivary agglutinin ( SAG ) protein gp340, a member of the scavenger receptor cysteine-rich ( SRCR ) superfamily of proteins and protein splicing discrepancy of the Deleted in Malignant Brain Tumors I ( DMBT1 ) that can be either secreted or membrane-bound which may be involved in transcytosis of HIV.
Potential paths of HIV transmittal: a ) Direct infection of epithelial cells. B ) Transcytosis through epithelial cells. degree Celsius ) Transmigration of septic giver cells. vitamin D ) Consumption by migratory intra-epithelial Langerhans cells. vitamin E ) Direct entry through breaches in the epithelial bed.
Beginning: Shattock & A ; Moore 2003 ( ref )
Glycoprotein-340 ( gp340 ) is a human protein splicing discrepancy of the Deleted in Malignant Brain Tumors I ( DMBT1 ) . DMBT1 has been identified as a member of the scavenger receptor cysteine-rich ( SRCR ) household of proteins, which are known for their function as pattern acknowledgment receptors for interactions with specific pathogen motives that drive signaling events ( refs ) . Differentially spliced discrepancies of DMBT1 were reported to be both as secreted signifiers or as membrane associated proteins ( refs ) . Abundant look has been found in tissues such as the lung, windpipe, salivary secretory organs, tummy and little bowel while minor look has been found in the testicle, mammary secretory organs, uterus and encephalon ( ten ) . The gp340 protein, a cell membrane associated splice discrepancy of DMBT1 has been found to be expressed at high degrees in the lung and upon acknowledgment of specific pathogen motive has been shown to excite the migration of alveolar macrophages ( refs ) . The gp340 protein, as the salivary agglutinin ( SAG ) protein, is the secreted splicing discrepancy of DMBT1 found in spit and was ab initio identified based on its function in the clearance of bacterial pathogens including S. mutans by originating clearance through agglutination and opsiniztion ( refs ) . SAG was the first DMBT1 splicing discrepancy to be identified to play a function in HIV infection ( refs ) . Compared to vaginal transmittal, HIV transmittal within the unwritten pit is low despite the presence of similar cell types in both unwritten and vaginal tissues. Fractionation of human spit led to the designation of SAG as an inhibitor of HIV infection in the unwritten pit ( refs ) . It was shown that SAG interaction with HIV leads to viral agglutination ( x ) . Immunoprecipitation assays showed that SAG binds to gp120 in an country different from the CD4 binding site, and it was reported that pretreatment of HIV with soluble CD4 resulted in enhanced SAG-gp120 binding ( x, ten, ten ) . Further surveies revealed that SAG interacts with HIV within the base of the V3 cringle, an country that is good conserved within the viral genome ( x, ten and Fig. 1.4 ) . While the function of SAG in HIV biological science has been studied in great item, the function of epithelial cell surface gp340 in HIV transmittal across venereal mucous membrane has merely late begun to be characterized. Stoddard et al reported that gp340 is expressed on vaginal and cervical tissues and that the cells showing the cell surface associated signifier of gp340 are capable of adhering and easing HIV transmittal. Since HIV is capable of interacting with epithelial cells surface gp340, it is possible that this receptor may play a function in the manner mucosal epithelial cells sense viral antigens and trigger immune activation.
Fig.1.4: Model picturing interaction of gp340 SRCR sphere with gp120: a ) Model of the quatinary composite between gp120, CD4, AB17b, and the SRCR sphere on gp340. B ) Space make fulling theoretical account of interaction between gp120 and SRCR domain on gp340.
Beginning: Wu et al 2004 ( ref )
B.3. Thymic Stromal Lymphopoietin ( TSLP )
It is known that mucosal epithelial cells secrete thymic stromal lymphopoietin ( TSLP ) in response to allergens and bacteriums ( refs ) . TSLP is an IL-7 similar cytokine that was originally identified in the supernatants of the mouse thymic stromal cell line, Z210R.1 and was reported to expose a singular ability to back up the long-run growing of a pre-B cell line every bit good as upregulate the proliferation of thymocytes ( ref ) . Isolation of a complementary DNA ringer encoding human TSLP revealed that it is structurally similar to murine TSLP but portions merely 43 % amino acerb homology. The TSLP receptor composite is a heterodimer consisting of a TSLP receptor ( TSLPR ) binding concatenation and the interleukin 7 receptor-I± ( IL-7RI± ) concatenation, together bind TSLP with a high affinity ensuing in Signal Transducers and Activator of Transcription-5 ( STAT-5 ) activation and cell proliferation23-26. Early surveies demonstrated that unlike murine TSLP, the human TSLP does non advance the distinction and growing of B cells nor does it hold a direct consequence to back up the activation of T cells ( refs ) .
In worlds, TSLP is chiefly expressed by tegument keratinocytes, epithelial cells, smooth musculus cells, lung fibroblasts, or IgE stimulated mast cells. Microbial infection or allergen exposure triggers mucosal epithelial cells to bring forth TSLP23 ( Fig.1.5 ) . TSLP strongly up-regulates activation markers such as CD54, CD80, CD83, CD86, DC-SIGN, and HLA-DR on myeloid dendritic cells ( mDC ) and activates immature DC to bring forth the neutrophil and eosinophil attractant chemokines Interleukin-8 ( IL-8 ) and eotaxin-2 every bit good as the T assistant 2 ( Th2 ) attractant chemokines Thymuss and activation regulated chemokine ( TARC or CCL17 ) and macrophage-derived chemokine ( MDC or CCL22 ) . Unlike the DC activated by a assortment of factors, such as CD40-L, LPS and poly I: C, TSLP-activated DC do non bring forth IL-12, TH1 responses, or the pro-inflammatory cytokines TNF, IL-1I? , and IL-6 ( ref ) . Alternatively, mature TSLP-activated DC migrate to the run outing lymph node and express high degrees of OX40L, which triggers the homeostatic proliferation and distinction of naA?ve CD4+ T cells into a alone type of inflammatory Th2 cells that produce Interleukin-4 ( IL-4 ) , Interleukin-5 ( IL-5 ) , Interleukin-13 ( IL-13 ) , and Tumor Necrosis Factor ( TNF ) and non the authoritative Th2 cells that produce Interleukin-10 ( IL-10 ) in the topographic point of TNF. These inflammatory Th2 cells so migrate back to the site of redness due to the local production of TARC and MDC. These surveies suggest that TSLP produced by epithelial cells plays an of import function in bring oning allergic inflammatory responses. This hypothesis is supported by surveies that show that the airway epithelial tissue of asthma patients expresses increased degrees of TSLP ( 25 ) and that infection by rhinoviruses or exposure to pro-inflammatory go-betweens such as IL-1I? , TNF-I± and some TLR agonists induce TSLP production in human air passage epithelial cells doing the aggravation of asthma ( 26 ) . Furthermore, TSLP is extremely expressed in patients with acute and chronic atopic dermatitis lesions ( ref ) and this increased TSLP look is associated with Langerhan cell migration and activation ( Ito et al JEM 2005 ) proposing that TSLP is a critical nexus between epithelial cells and the DC of the immune system at a molecular degree. The fact that TSLP produced by epithelial cells exposed to allergens and bugs induces DC-mediated enlargement of CD4+ T cells formed the footing for the cardinal hypothesis of this thesis research that: Hiv exposure at the mucosal tissues stimulates epithelial cells to bring forth TSLP for DC-mediated enlargement of susceptible mark CD4 T cells.
In 2007, Lee and Ziegler identified an NFI?B site within the human TSLP cistron booster that was critical for IL-1I? and TNF-I± induced TSLP look. This provided a nexus for the mechanism by which TSLP look is induced by ligands for TLR2, TLR8, and TLR9. Since NFI?B has such a wide scope of activation signals, several labs explored the possible engagement of other factors for modulating TSLP look. Li et Al. identified two atomic receptor adhering sites in both the human and mouse TSLP cistron boosters, in peculiar the retinoid Ten receptors ( RXR ) I± and I? for which 9-cis- retinoic acid ( 9-cis-RA ) serves as a high-affinity ligand ( ref ) . Surveies showed that keratinocytes with selective extirpation of RXRI± and RXRI? display an inflammatory response similar to that of atopic dermatitis in worlds. ( ref ) . High degrees of TSLP look were besides found in these cells. In 2008, Lee et Al. demonstrated that 9-cis-RA represses IL-1I? mediated TSLP cistron look through direct suppression of NFI?B binding and signaling. These surveies suggest that RXRI± and RXRI? , when edge to ligand, are involved in modulating TSLP look and, combined with my consequences from the probe, could offer new penetrations into developing fresh curative schemes in the battle against the transmittal of HIV.
Fig.1.5: Pathology of TSLP in allergic redness
Microbial infection or allergen exposure triggers mucosal epithelial cells to bring forth TSLP. TSLP activates immature DC to bring forth the neutrophil and eosinophil attractant chemokines Interleukin-8 ( IL-8 ) and eotaxin-2 every bit good as the T assistant 2 ( Th2 ) attractant chemokines Thymuss and activation regulated chemokine ( TARC or CCL17 ) and macrophage-derived chemokine ( MDC or CCL22 ) . Matured TSLP-activated DC migrate to the run outing lymph node and express high degrees of OX40L, which triggers homeostatic proliferation and distinction of naA?ve CD4+ T cells into inflammatory Th2 cells that produce Interleukin-4 ( IL-4 ) , Interleukin-5 ( IL-5 ) , Interleukin-13 ( IL-13 ) , and Tumor Necrosis Factor ( TNF ) . These inflammatory Th2 cells so migrate back to the site of redness due to the local production of TARC and MDC. .
Beginning: Y.J. Liu, 2006 ( ref )