GBV-C is a member of the Flaviviridae family. This virus has a single-stranded RNA genome exhibiting a positive polarity that is capable of encoding about 3,000 amino acids. Based on phylogeny, GBV-C is about 30% homologous with Hepatitis-C virus (HCV) (Leary and others 1996). Replication of HCV and GBV-C occurs in different type of cell; that of HCV occurs primarily in hepatocytes while that of GBV-C occurs usually in B-lymphocytes and T lymphocytes particularly CD+ and CD8+.
In terms of extensiveness of glycosylation of the glycoprotein envelope (E2), GBV-C is extensively glycosylated unlike the HCV. Also during GBV-C infection there is no traced presence of antagonizing antibodies unlike in HCV wherein there is detectable presence of antibodies. The antibody against GBV-C viremia called anti-E2 is detected only after clearance from the GBV-C infection and this antibody prevents reinfection from GBV-C. In addition, presence of anti-E2 may be used as a marker of past infection from GBV-C (Stapleton, Williams, & Xiang, 2004.
In a review made by Maidana (2005) she provided a good description of the virus GBV-C as what has been discovered in various studies. The nontranslated region (NTR) at 5’ of the GBV-C has a function of directing the translation of the uncapped RNA message inside the ribosome (Simons, Desai, & Schultz, 1996). Two structural glycoproteins that constitute the HIV viral envelope protein seemed also to be encoded by GBV-C. The composition of the nucleocapsid of this virus is however is not yet characterized.
At present there are 5 identified genotypes of GBV-C (Okamoto, Nakao, & Inoue, 1997; Tucker, Smuts, & Eickhaus, 1999). These 5 genotypes differ in area of prevalence in which genotype 1 is usually found in West Africa; genotype 2 predominates in USA and Europe; genotype 3 in Asia; genotype 4 in Southeast Asia; and genotype 5 in South Africa (Tucker & Smuts, 2000). Parenteral routes accounts for the greatest transmission of GBV-C and this is common among medically unadministered users of intravenous drugs (Frey, Homan, & Sokol-Anderson, 2002; Pomerantz & Nunnari, 2004).
The extremely low density of GBV-C permits its interaction with lipids in the blood serum among humans. Entrance into target cells as well as attachment of GBV-C with other viruses can be aided by low-density lipoprotein receptor(Xiang, Wunschmann, & Schmidtt, 2000). Clearance from this virus is a common occurrence among immunocompetent infected individuals and this occurs at an approximated rate of 60 to 70 % and clearance may also be followed by the formation of antibodies against the envelope glycoprotein E2 (anti-E2)(Xiang, Wunschmann, & Schmidtt, 2000).
The presence of anti-E2 is often used as an indication of the history GBV-C infection. Studies up to date have shown that GBV-C infection is not known to cause any that is why the Food and Drug Administration (FDA) has not ordered yet the blood screening of donors for this particular virus but some still remains skeptic about this. As to the prevalence of this virus, 1. 8% of American blood donors and more than 35% of the HIV-infected subjects are positive (Dawson, Schlauder, & Pilot-Matias, 1996).
Infection with GBV-C can be detected through reverse transcription polymerase chain reaction (RT-PCR) or a branched DNA (bDNA) assay. The studies discussed below are among the numerous studies that have contributed in the strengthening of the assertion that coinfection of HIV positive patients with GBV-C merits positive results such as delay of the progression of HIV and better survival rates over a length of time when compared with patients who do not have any history of infection with the said virus.
The prevalence of GBV-C RNA and anti-E2 antibody among 197 HIV-infected patients and 120 control blood donors were studied by Heringlake and colleagues. Results revealed the percentage of GBV-C RNA among HIV infected patients as much greater than the control blood donors with 16. 8% and 0. 8% respectively (Heringlake et al. , 1998). The CD4+ cell counts were found out to be significantly higher in GBV-C-viremic patient. Also better survival was manifested by HIV-infected patients who are GBV-C RNA-positive. This suggests that that GBV-C might be a favorable prognostic factor in HIV disease.
In a certain study which was also anchored to study more about the GBV-C, survival rates of patients with GBV-C in comparison with those with GBV-C during 16 years of follow-up after HIV seroconversion was determined. The variables included were age, CCR5 genotype, HIV and HCV viral loads, CD4+ and CD8+ lymphocyte counts, and GBV-C or anti-E2 antibodies. It was found out that GBV-C positive patients had higher CD4+ lymphocyte counts. The risk for AIDS was 40% lower among GBV-C positive than GBV-C negative patients and was not affected by HIV and HCV viral loads, CD4+ and CD8+ lymphocyte counts, and CCR5 genotype.
However, there was no mechanism provided that will ascertain the interaction of GBV-C with HIV (Yeo et al. , 1998). In September 2001, two studies published in the same journal, The New England Journal of Medicine, determined the effect of co-infection of HIV-positive patients with GVB-C on the survival rates of the patients. In the first study done by Xiang and his colleagues, the effect of coinfection of HIV patients with GBV-C on the survival of patients was determined.
In vitro replication of peripheral-blood mononuclear cells (PBMC) coinfected with GBV-C and HIV was performed in order to determine if GBV-C could alter the replication process. From the study, 39. 8 % of the 362 HIV-positive patients showed positive GBV-C viremia of which 41% died during the follow-up period, while 56. 4% of the negative GBV-C patients died at the same period. The mortality rate in this 4. 1 year long study is found to be significantly higher among HIV-positive patients with negative GBV-C. The mortality rates was independent that of anti-HIV therapy/prophylaxis, CD4+ count, age, race, sex, and mode of HIV transmission.
The quantity of p24 antigen in the PBMC-GBV-C coinfection culture showed that the replication process of HIV was disrupted. It was also said that GBV-C replication is noncytopathic thus cellular toxicity was not accounted for as the effect of HIV replication. GBV-C replication appeared to take action during HIV replication prior to attachment and entry as supported by viral infection not disrupting the expression of CD4, CXCR4, or CCR5. Hence, it was concluded from this study that GBV-C and HIV coinfection can significantly improve the survival rates of the HIV-infected patients(Heringlake et al. , 1998).
In the second study conducted Tillmann and his colleagues, 197 HIV-positive patients were followed starting in 1993 or 1994. Of which, 16. 8 % tested positive for GBV-C RNA, and 56. 9 % had detectable anti-E2 while 26. 4 % had no marker of GBV-C infection and were assumed to be negatively exposed. For the patients with GBV-C RNA infection the survival was significantly longer and the progression of AIDS was slower. Furthermore, there was also a better survival after development of AIDS. There was a negative correlation between the HIV load and GBV-C load but GBV-C load did not correlate with CD4+ cell count.
As to the better survival of the anti-E2 positive patients compared with GBV-C RNA negative patients, the previous exposure to GBV-C viremia may account for this. Hence it was concluded that GBV-C viremia may relate to a decreased mortality of HIV-positive patients. Also it may account for slower progression to AIDS and longer survival upon seroconversion to AIDS. The authors also proposed that the delayed progression of HIV during coinfection is due to the inhibition of HIV replication by the GBV-C. GBV-C infection could also be a marker for the presence other factors which results into a decreased rate of AIDS progression.
Elucidation of the mode of action of GBV-C in inhibiting the replication of HIV may give rise to invention of therapeutic approaches for HIV infection (Tillmann et al. , 2001). In 2004, two notable studies from USA and Sweden published significant results regarding this contested issue. As mentioned by Whol (2004) these two research teams arrived at different interpretations about the result of their study but arrived with similar results in some tested variables. The research team from the USA provided some insights regarding the possible discovery of a therapeutic approach to HIV treatment.
The other team from Sweden implied the possible relationship of GBV-C with HIV progression but he strongly refuted that GBV-C-HIV coinfection phenomenon could be considered as independent prognostic factor (Whol, 2004). In the study of Williams’ team, GBV-C viremia and anti-E2 were measured among 271 men patients from the Multicenter Acquired Immunodeficiency Syndrome Cohort Study, USA. Two tests were conducted; the first one was after 12 to 18 months of HIV seroconversion and this was designated as the early visit and the second one was after 5 to 6 years after HIV seroconversion and was marked as the late visit.
It was found out that GBV-C infection is prevalent among the patients (85%) in which positive GBV-C infection detected through presence of GBV-RNA accounts for 39 % of the occurrence while through presence of anti-E2 accounts 46% of the occurrence. Based from the results, observation of the GBV-C status after 12 to 18 months after seroconversion (early visit) was not conclusive in associating with rates of survival. In contrast with the early visit, the late visit which occurred 5 to 6 years after seroconversion provided significant results. The occurrence of the death of patients without GBV-C RNA was 2.
78 times greater than those with persistent GBV-C viremia, in which the loss of GBV-RNA is associated with the poorest prognosis. This lead the authors to conclude that GBV-C viremia is significantly related to prolonged survival among the HIV patients observed but this is only true after 5 to 6 years of HIV seroconversion and not after 12 to 18 months. In essence, the authors provided an insight about the usefulness of undermining the mechanism of interaction between GBV-C and HIV in predicting the progression of AIDS (Williams et al. 2004). In the abovementioned study, possible confounders were also tested to eliminate inconsistencies.
One of these is the possible effect of viral hepatitis pathogens but this was deemed insignificant since these pathogens occurred only at low rates with 6% and 5% for hepatitis-B virus and hepatitis-C virus respectively. The other one is the prevalence of heterozygosity for polymorphism of the CC chemokine receptor 5 (CCR5) with a prevalence rate of 8% (Williams and others 2004). Moreover, it was reported that the survival benefit is greater than that reported for men in the Multicenter AIDS Cohort Study who are heterozygous for the CCR5 32. It must be noted that CCR5-?
32 is a genetic defect affecting the human immune system that has both harmful and beneficial effects. It is a deletion mutation of a gene specifically impacting the function of T cells multiple studies of HIV-infected persons have shown that presence of one copy of this gene delays progression to the condition of AIDS by about 2 years. A person who has a CCR5-? 32 receptor gene may possibly be not infected with HIV R5 strains. However, the research team remained ignorant about the relation of GBV-C clearance with the progression HIV infection.
It was not known if the GBV-C clearance was mediated by the accelerated growth of HIV, which in turn depleted the host cell CD4+ for GBV-C or if the loss of GBV-C resulted first into the depletion of CD4+ cells. From what the authors discussed, GBV-C clearance was more likely to be associated as a prognostic factor of HIV progression and independent with the possible confounding factors tested. HIV can be classified into two: the nonsyncytium inducing or macrophage (M- tropic) and syncytium inducing viruses (T-tropic).
The M-tropic HIV virus usually infects PBMC and macrophages and usually abundant at early developmental phase of HIV seroconversion while T-tropic usually infects T cell lines and PBMC and usually characterizes the development of the disease AIDS (Tersmete et al. , 1989). These two strains of HIV viruses use different kind of chemoreceptor to aid passage into target cells of a host. While the M-tropic HIV virus use CC chemokine receptor 5 (CCR5) the T-tropic HIV virus uses CXC chemokine receptor 4 (CXCR4) (Alkhatib et al. , 1996).
Chemokines such as MIP-1a, MIP-1b, and RANTES may use also the CCR5 receptor and when this happens they block the interaction of the gp 120 portion of the viral envelope glycoprotein of the M-tropic HIV virus with CCR5 receptor, hence may lead into some therapeutic effects(Combadiere, Ahuja, Tiffany, & Murphy, 1996; Dragic et al. , 1996; Margolis, Glushakova, Grivel, & Murphy, 1998). According to the review made by Maidanal (2005) GBV-C particularly induces the upregulation of the chemokine RANTES but the specific mechanism as to why this phenomenon occur still remains unanswered.
In the same year as the MACS’ study was published, similarly designed study from Sweden by Bjorkman and his colleagues concluded otherwise. In their study serum sample of 230 patients who were diagnosed within 2 years of HIV infection were examined prior to the patients’ antiretroviral treatment, death or last correspondence with the regular clinical check-ups. The presence of GBV-C RNA and anti-E2 were tested at the onset of the check-up and marked as the baseline sample while the latest assessment was marked as the follow-up sample.
Assessment of the baseline samples revealed that GBV-C was not related with mortality. Moreover, it was also observed that patients who lack anti-E2 when compared with patients who have persistent anti-E2, persistent absence of anti-E2 and acquisition of GBV-C viremia exhibited significantly a greater mortality rate. The authors found out that the detection of the presence of GBV-C viremia does not provide consistent results concerning the prediction of the pattern of development AIDS. Along with this, GBV-C viremia is uncommon among the patients and lost of GBV-C viremia was not accompanied by anti-E2 formation.
Hence, the research team concluded that the loss of GBV-C viremia among HIV-infected patients could be an occurrence secondary to HIV progression. Thus, GBV-C status examination can not be used as an independent indicator in the developmental course of AIDS (Bjorkman et al. , 2004). Summing up the conclusion of the two research teams: while Williams’ team arrived at concluding the possibility of using the mechanism of GBV-C and HIV interaction to predict the progression of AIDS Bjorkman’s team concluded that this does not provide conclusive results and that GBV-C phenomenon is more of an independent occurrence secondary to HIV progression.
Smith et al. (2005) evaluated the prevalence of antibodies against GBV-C envelope glycoprotein E2 and GBV-C viremia in an HIV-positive inner city population predominantly African-American. He found out that subjects with GBV-C viremia and anti-E2 antibodies manifested undetectable HIV-1 viral load. It was also affirmed that GBV-C viremic patients with HIV-1 respond better to therapy. In a meta-analysis conducted by Zhang et al.
, it was sought to elucidate from the existing studies the effect of HIV coinfection with GBV-C on the survival of HIV-positive patients and as well as to estimate the effect Studies were classified whether there the appearance of GBV-C was during an early or late HIV disease. Hazard ratio (HR) of death for GVB-C infected HIV patients against those lacking the virus was the primary measure use. There was no causal relationship between the survival and GBV-C infection during early HIV infection(Zhang, Chalone, Tillmann, Williams, & Stapleton, 2006).
In contrast, there was a significant decrease in the hazard mortality among patients with HIV-GBV-C coinfection at later part of the HIV infection. The conclusion of the study supports that of Williams and her colleagues in which the timing of GBV-C infection accounts for the contrasting results of studies on the effect of GBV-C coinfection on survival of HIV-infected people (Williams et al. , 2004). The mechanism by which GBV-C acts against HIV remains as question for there have been no studies clearly elucidating the process involved.
In a certain study conducted is observed that there is an alteration of the cytokine profile among patients exhibiting coinfection. In the patients who are coinfected the level of type 1 helper T (Th1) cytokines like interleukin-2 is normal to elevated while for GBV-C negative there is an increase in level of type 2 helper T (Th2) cytokines like interleukin-4 and interleukin-10 and a decrease in the level of Th1 cytokines. This change in the level of helper T cells has shown to play an important role in the progression of AIDS.
In the onset of the disease there is normal to elevated Th1 cytokine profile but at the latter stages this gradually decreases as Th2 level gradually increases. This immune-based mechanism may be one of the actions of GBV-C and HIV coinfection (Pomerantz & Nunnari, 2004). In Pomerantz and Nunnari’s study (2004) virologic and immunologic variables among HIV-positive patients who have GBV-C and do not have the virus were compared. Specifically the variables measured are the presence of GBV-C RNA, plasma HIV viral load, CD4+ cell count and levels of the interleukin-2 (IL-2), IL-4, IL-10, and IL-12.
Among the GBV-C negative patients, levels of the interleukins particularly observed differed from the early and follow-up observation. Initially the level of IL-2 and IL-12 were high but significantly decreased during the follow-up the reverse is true for IL-4 and IL-10, which significantly increased during the follow-up observation. Another mechanism could be through the direct reduction of the HIV replication as affected by GBV-C. This is supported by the study conducted by Xiang published in 2001.
It must be recalled that HIV and GBV-C can both infect and replicate in PMBC hence through this manifestation of the same cell tropism the two viruses could possibly interact directly or indirectly with each other. Maidana et al. (2005) said that “GBV-C may affect the different points of the HIV life cycle and these could be during the retroviral binding to target cells by the high-affinity receptor CD4 and several chemokine coreceptors, internalization and reverse transcription, integration into the host-cell genome to create the HIV provirus, viral transcription and translation, and viral morphogenesis and budding. ”