Replication of TT virus in hepatocyte and leucocyte cell lines.

The TT virus (TTV) is a non-enveloped, single-stranded, circular, DNA virus, first isolated from a patient with hepatitis of unexplained etiology. The much deliberated pathological role of the virus continues to be conjectural in the absence of a suitable in vitro replication model. So far, the liver and the bone marrow have been shown to be the main sites of TTV replication. In this study, the human cell lines HepG2 and Chang Liver, the rat hepatoma cell line MH1C1, phytohemagglutinin (PHA)-stimulated TTV-negative peripheral blood mononuclear cell (PBMC) cultures and the B lymphoblast cell line, Raji were investigated as potential in vitro replication systems for TTV. The cell lines were infected with an inoculum prepared by pooling TTV genotype1 DNA positive sera and monitored for virus replication. Of the three hepatocyte cell lines, while the HepG2 and MH1C1 cell lines did not support TTV replication, the Chang Liver cell line showed clear morphological changes as a result of the in vitro infection, which included clumping and granular degeneration of the entire cell sheet over a period of 6 days. The infected cells also showed presence of virus-specific mRNA representative of viral transcription. The consistent presence of infectious viral particles in the supernatant culture fluid at 24-hr fluid replacement intervals indicated limited extra-cellular release of viral particles. The PHA-stimulated TTV-negative PBMC cultures and the Raji cell line were also able to support TTV replication and released significant levels of infectious viral particles into the supernantant culture fluid.

Molecular epidemiology and clinical implications of TT virus (TTV) infection in Indian subjects.

GOALS: This study was aimed at obtaining data on the epidemiology and clinical course of TT virus (TTV) infections among Indian subjects. BACKGROUND: The TTV is a nonenveloped DNA virus, first identified in the peripheral blood of individuals with posttransfusion hepatitis of unknown etiology. There has been much conjecture regarding the disease association of this virus. STUDY: A total of 494 serum specimens from various groups of high-risk and control subjects were screened for TTV DNA by a semi-nested PCR, using the ORF1-derived N22 primers. The sera were also screened for the HBsAg surface antigen by an ELISA, HCV RNA by a 5' NCR-based RT-PCR and GBV-C/HGV RNA by a 5' UTR-based RT-PCR. The clinical and hepatic profiles of the various subjects were also studied. Seventy-one randomly picked TTV isolates were directly sequenced and their phylogeny was studied. RESULTS: TTV showed an overall positivity rate of 45.34% with a significant higher prevalence of 52.9% among the high-risk subjects as against a prevalence of 28% among healthy control subjects (P < 0.001). Abnormal liver function profiles were frequent among TTV viremic individuals and among the acute hepatitis cases studied a higher mortality rate correlated with a superimposed TTV infection. The 71 TTV isolates sequenced were found to belong to genotype 1a being closely homologous to TTV prototype TA278. CONCLUSION: The TT virus shows a significant prevalence in the Indian population, particularly among subjects at risk for acquiring parenterally transmitted infections. Our study corroborates a putative role of the virus in the etiology of liver disease, particularly in coinfection with other agents.

GB virus C/hepatitis G virus infection in Indian blood donors and high-risk groups.

The hepatitis G virus (HGV) or GB virus C (GBV-C) was discovered in 1995 as a putative agent of post-transfusion, non-A-E hepatitis. The present study was carried out with the aim to find the prevalence of this virus among various subject groups at risk for parenteral transmission as well as in healthy control subjects both individually and along with other parenterally transmitted hepatitis viruses. Of the 402 subjects tested, 6.22% were positive for the HBsAg surface antigen, 7.21% were positive for HCV RNA while only 2.24% were seen to be carriers of the HGV/GBV-C RNA. All the HGV/GBV-C positive cases were either multi-transfused thalassaemic subjects or hemodialysis patients. None of the healthy control subjects showed presence of the virus. Seven of the HGV/GBV-C positive subjects showed co-infection with one or more additional virological markers. Also, of the 9 HGV/GBV-C positive subjects, 5 showed elevated ALT levels while 4 showed elevated alkaline phosphatase levels. Overall our findings seem to indicate that HGV infections generally are asymptomatic, transient and self-limiting and the virus does not seem to show a very high prevalence among the Indian population.