By T. Falk. The Baptist College of Florida.
HPgV has until yet not been shown to cause any known disease in humans but a couple of studies indicated a more favourable course of HIV- generic aurogra 100mg without prescription erectile dysfunction low blood pressure, HCV- cheap 100mg aurogra overnight delivery impotence postage stamp test, and more recently Ebolavirus-associated diseases (Lauck 2015) in those individuals chronically coinfected with HPgV. Prevalence studies revealed HPgV viremia within the general population ranging from less than 5% in industrialized countries up to more than 15% in some devel- oping countries. Although approximately 10% to 30% of blood donors have specific antibodies against HPgV, affected individuals are not excluded from the donation of blood, assuming that the virus is apathogenic. Consequently, serological diagnostics on HPgV are not routinely performed. An estimated 25% of HPgV-infections persist, and the other 75% clear viremia within two years of infection (Gutierrez 1997; Tanaka 1998). Two serological markers for HPgV infection exist: HPgV viremia can be deter- mined using a PCR method; and antibodies to the envelope region E2 (anti-E2) are detected by ELISA (Table 1). As they are mutually exclusive, either HPgV viremia or the presence of anti-E2 is detectable in HPgV infected individuals (Gutierrez 1997; Tanaka 1998). HPgV viremia may persist for decades but in the majority HPgV viremia is transient and ends with seroconversion to anti-E2, resulting in immunity to new infections. However, this does not seem to be a lifelong immunity (Table 1). Hence coinfection of human HPgV and HIV is common and persistence of HPgV viremia (HPgV RNA positivity) is prolonged in HIV infection. Until now six genotypes and several subtypes of HPgV have been described with significant variation in their regional distribution and in virologic characteristics. Table 1: Serological markers and stages of HPgV infection Marker Pegivirus-C-Viremia (RNA) Anti-E2-Antibodies Method PCR / b-DNA ELISA HPgV negative negative negative Replicative HPgV-C Infection positive negative Past HPgV-C Infection negative positive / (negative)* * Anti-E2-antibodies may disappear over time HIV and HPgV coinfection: Pas de deux In 1998 the first cohort studies described a modulating impact of HPgV coinfection on HIV-infection (Toyoda 1998, Heringlake 1998): The HPgV viremic subgroup pre- sented with lower HIV viremia, higher CD4 T cell counts, slower progression to AIDS and improved survival as compared to the HPgV non-viremic patients. These bene- ficial effects were confirmed by different research groups (Lefrère 1999, Yeo 2000, Tillmann 2001, Xiang 2001) and were also seen in antiretrovirally treated HIV+ indi- viduals (Tillmann 2004+2006, Nunnari 2003, Williams 2004, Ernst 2011). The mod- ulatory effects were associated to persisting HPgV viremia but were not present in those without or with cleared HPgV infection. A meta-analysis described an improved response to ART and clinical benefit for HIV/HPgV coinfected patients, which was more pronounced with longer follow-up (Zhang 2006). Conflicting results came from some studies (review: Battharai 2012), which did not find an effect of HPgV viremia on HIV infection (Sabin 1998, Birk 2002, Bjorkman 2004, van der Bij 2005), including two studies in women (Kaye 2005, Williams 2005). One of these studies summarized viremic and anti-E2-positive patients as HPgV pos- itive group (Sabin 1998). Another study focused on HPgV viremia at study entry (van der Bij 2005). In this study the subgroup with persistent HPgV RNA had a superior clinical outcome. A less pronounced potential gender-specific modulating effect of HPgV on HIV in women may exist (Kaye 2005, Williams 2005). Another study on HIV+ pregnant women found a lower HIV viral load in HPgV viremic mothers and less vertical HIV transmission in the HAART era but not in the pre-HAART era (Handelsman 2008). The lower risk for vertical transmission of HIV seems to be asso- ciated with replicative HPgV infection in the child rather than by HPgV status of the mother. Surprisingly the risk for vertical transmission of HPgV was found to be increased under HAART in HIV/HPgV coinfected pregnant women (Bhanich-Supapol 2009). In addition, there is evidence from a multicenter trial, that HPgV genotype 2 coinfection was associated with higher CD4 T cell counts (Schwarze-Zander 2006). This may explain regional differences and at least in part conflicting results from cohort studies from different regions. In summary, most studies found more pronounced antiretroviral and immunologi- cal effects in ART-treated HPgV RNA positive patients. No study to date described a negative influence of HPgV viremia on the effect of ART. Human Pegivirus HPgV Infection 469 Table 2: Potentially beneficial effects of replicative HPgV coinfection on HIV disease Increase Decrease • CD4+ T cells • HIV plasma viremia • Response to ART • Mother to child transmission of HIV • Survival • Progression to AIDS or death • Quality of life • Proportion of naïve CD4+ and CD8+ T cells; • T cell activation: T cell activation markers number of double negative T cells (CD25, CD38, and CD69), cytotoxic CD8+ (CD3+/CD4-/CD8-); immunosuppressive T cell functions, T cell-receptor signaling cytokines (TGF-ß, IL-10) HPgV, HIV, and HCV: Ménage à trois Triple infected patients with HIV, HCV and HPgV had less progressed liver disease as compared to those without HPgV infection (Barbosa 2009, Berzsenyi 2009), and an improved response to interferon/ribavirin therapy of HCV (Hofer 2011) indicat- ing as well a potential interdependency of HPgV with HCV. However, if harm reduction is exclusively seen in the chronically replicative HPgV/HIV coinfection – is it then necessary to keep HPgV viremia ongoing like a tamagotchi game?
TCR GERMLINE Diﬀerent TCR germline loci somatically recombine and mutate to gen- erate the DNA that codes for the variable buy discount aurogra 100mg on-line erectile dysfunction treatment ring, antigen-binding part of the TCR (Janeway et al aurogra 100mg lowest price impotence underwear. These generative mechanisms allow each individual to produce a huge variety of TCR binding speciﬁcities. The intensity of direct selection on germline polymorphisms may be rather weak because speciﬁc recognition of antigens depends primarily on somatic mechanisms to create variability. However, the germline alleles do set the initial conditions on which somatic processes build, so it is certainly possible that germline polymorphisms inﬂuence individual tendencies to react to particular antigens. The limited data currently available indicate that some germline poly- morphisms exist for the TCR (e. One interesting study found an interaction between a human germline polymorphism in a subunit of the TCR (VA8. Individuals with enhanced allergic response to a dust mite antigen tended to have one of the two VA8. Most likely, the TCR and MHC class II polymorphisms inﬂuence IgE via helper Tcells—TCR binding to antigens presented by MHC class II stimulates helper T cells, which in turn play a role in antibody stimulation. Thus, speciﬁc recognition by the TCR and MHC can aﬀect speciﬁc recognition by antibodies (Shirai et al. Diﬀerences between species do not directly inﬂuence antigenic variation in parasites unless the parasites infect diﬀerent species. But phylogenetic comparisons may illuminate the forcesthatshape TCR germline variability within species. BCR GERMLINE The variable portion of the B cell receptor (BCR) develops by somatic recombination and mutation similar to the processes that generate vari- able TCRs. I found only one report of a major germline polymorphism in the alleles that make up the variable components of the BCR. Thesamepolymorphic alleles at asingleBCRgermline locus occur in both rabbits and snowshoe hares, suggesting that this polymorphism was inherited from a common an- cestor and maintained for a long time in each species (Su and Nei 1999). Hauser (1995) suggested that somatic hypermutation (aﬃnity matura- tion) of the BCR provides a buﬀer between the germline and the matured BCR speciﬁc for particular antigens. The TCR has limited somatic muta- tion after the initial genetic recombinations, perhaps exposing germline TCRs to more intense selective pressures than BCRs. However, lack of observed variability in germline BCR genes may simply reﬂect limited study. MATCH TO VARIANT CELLULAR RECEPTORS Major deletions of cellularreceptor genes can interfere with parasites that depend on those receptors for binding or entry into cells. For exam- ple, the human CCR5 gene encodes a coreceptor required for HIV-1 to enter macrophages. A 32-bp deletion of this gene occurs at a frequency of 0. This deletion prevents the virus from entering macrophages (Martinson et al. Hill (1998) reviews cases in which variations in the hosts’ vitamin D and other cellular receptors are associated with susceptibility to various diseases. It is not clearwhetherminor variants of cellular receptors occur suﬃciently frequently to favor matching variation of parasites for attachment to those receptors. TH1response typically stimulates CTL proliferation, whereas TH2response typically stimulates antibody pro- duction. Several studies have found genetic variation among hosts in the reg- ulation of TH1versusT 2rH esponse. In mice, the actions of multiple genetic loci combine to determine regulation of TH1versusTH2against Leishmania infections (Coﬀman and Beebe 1998; Power 2000). Mice that develop a TH1response control infection because Leishmania can be cleared by CTLs. By contrast, those mice that develop a TH2response fail to clear infection because Leishmania cannot be controlled by a dom- inant antibody response. In pigs, polygenic control has been observed forseveral traits in- cluding antibody response, with an important contribution of non-MHC loci; proliferative and cytokine responses of mononuclear blood lym- phocytes, such as T cells, B cells, and natural killer (NK) cells; T cell– mediated inﬂammatory response to innocuous antigens (delayed-type hypersensitivity); and the total number and relative proportions of the various kinds of blood-borne immune cells (reviewed by Edfors-Lilja et al. High heritabilities have been estimated for several of these traits. Studies of other organisms have alsofound polygenic control of quan- titative immune responses outside the MHC region (Biozzi et al. Linkage studies of mice have begun to map locations of genes that in- ﬂuence quantitative variability in components of immunity (Puel et al.
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