Immune response to the pre-S(1) region of the hepatitis B surface antigen (HBsAg): a pre-S(1)-specific T cell response can bypass nonresponsiveness to the pre-S(2) and S regions of HBsAg

Hepatitis B surface antigen (HBsAg) particles are composed of a major polypeptide, p25, and additional polypeptides of higher m.w., namely p33 and p39, are variably present. All three polypeptides share the 226 amino acid residues of the S region: p33 consists of the p25 sequence plus an NH2-terminal 55 residues (pre-S(2], and p39 consists of the p33 sequence plus an NH2-terminal 108-119 residues (pre-S(1). In previous studies we demonstrated the influence of two Ir genes on the humoral and cellular immune responses to the S region and identified nonresponder phenotypes (H-2f,s). Subsequent studies showed that the immune response to the pre-S(2) region was regulated by H-2-linked genes independently of the S region response, such that immunization of S region nonresponder, pre-(S2) region responder mice (H-2s) with HBsAg/p33 circumvented nonresponse to the S region. In the present study, we have extended this analysis to the pre-S(1) region of HBsAg, with the following results: 1) and pre-S(1) region is immunogenic at the T and B cell levels; 2) anti-pre-S(1) specific antibody production is regulated by H-2-linked genes and can be independent of anti-S and anti-pre-S(2) antibody production; 3) immunization of H-2f strains with HBsAg/p39 particles containing the pre-S(1) region can bypass nonresponsiveness to the S and pre-S(2) regions in terms of antibody production; 4) two synthetic peptides, p32-53 and p94-117, define murine and human antibody binding sites on the pre-S(1) region, and p1-21 and p12-32 define additional human antibody binding sites; 5) pre-S(1)-specific T cells can be elicited in S and pre-S(2) region nonresponder mice (H-2f) and provide functional T cell help for S-pre-S(2)-, and pre-S(1)-specific antibody production; and 6) a T cell recognition site in the pre-S(1) region, p12-32 was identified. These results are relevant to HBV vaccine development, and possibly to viral clearance mechanisms, since the higher m.w. polypeptides are preferentially expressed on intact virions.     

Expression of hepatitis B virus large envelope polypeptide inhibits hepatitis B surface antigen secretion in transgenic mice.

The outer membrane of the hepatitis B virus consists of host lipid and the hepatitis B virus major (p25, gp28), middle (gp33, gp36), and large (p39, gp42) envelope polypeptides. These polypeptides are encoded by a large open reading frame that contains three in-phase translation start codons and a shared termination signal. The influence of the large envelope polypeptide on the secretion of hepatitis B surface antigen (HBsAg) subviral particles in transgenic mice was examined. The major polypeptide is the dominant structural component of the HBsAg particles, which are readily secreted into the blood. A relative increase in production of the large envelope polypeptide compared with that of the major envelope polypeptide led to profound reduction of the HBsAg concentration in serum as a result of accumulation of both envelope polypeptides in a relatively insoluble compartment within the cell. We conclude that inhibition of HBsAg secretion is related to a hitherto unknown property of the pre-S-containing domain of the large envelope polypeptide.     

The hepatitis B virus (HBV) precore protein inhibits HBV replication in transgenic mice.

In this study, we examined the ability of the hepatitis B virus (HBV) precore, envelope, and X gene products to modulate HBV replication in the livers of transgenic mice that replicate the virus. Hepatic HBV replication was not affected by overexpression of the envelope or X gene products when these animals were crossed with transgenic mice that express the corresponding viral genes in the hepatocyte. Overexpression of the precore protein, however, eliminated nucleocapsid particles from the cytoplasm of the hepatocytes and abolished HBV replication without affecting the hepatic steady-state content of pregenomic HBV RNA. These observations suggest that the precore protein can exert a dominant negative effect on HBV replication, presumably at the level of nucleocapsid particle maturation or stability, suggesting an important role for this enigmatic viral protein in the HBV life cycle.     

Expression of the hepatitis delta virus large and small antigens in transgenic mice.

Simultaneous infection with hepatitis delta virus (HDV) and hepatitis B virus (HBV) in humans is often associated with severe viral liver disease including fulminant hepatitis. Since HBV is thought to be noncytopathic to the hepatocyte, the enhanced disease severity observed during dual infection has been attributed to either simultaneous immune responses against the two viruses or direct cytotoxic effects of HDV products on the hepatocyte or both. To examine these alternate possibilities, we produced transgenic mice that express the small and large delta antigens (HDAg) in hepatocyte nuclei at levels equal to those observed during natural HDV infection. No biological or histopathological evidence of liver disease was detectable during 18 months of observation, suggesting that neither the large nor small form of HDAg is directly cytopathic to the hepatocyte in vivo.     

Hepatitis B virus nucleocapsid particles do not cross the hepatocyte nuclear membrane in transgenic mice.

Transgenic mice that express the hepatitis B virus core protein were used to examine factors that influence the intracellular localization of nucleocapsid particles in the primary hepatocyte in vivo. In this model, viral nucleocapsid particles are strictly localized to the nucleus of the hepatocyte except when the nuclear membrane dissolves during cell division, at which time they enter the cytoplasm. The cytoplasmic nucleocapsid particles do not reenter the nucleus, however, when the nuclear membrane re-forms after cell division. The data support the notion that nucleocapsid particles can form de novo within the nucleus, and they suggest that performed nucleocapsid particles cannot be transported across the intact nuclear membrane in either direction. The results imply that nucleocapsid disassembly is probably required for entry of the hepadnaviral genome into the nucleus, and they question the role of the intranuclear viral nucleocapsid particle during the viral life cycle.     

Hepatitis B virus replication is cell cycle independent during liver regeneration in transgenic mice.

The content of hepatitis B virus (HBV) replicative forms and HBV core protein in the liver of HBV transgenic mice is transiently reduced during massive liver regeneration following partial hepatectomy while the steady-state content of viral RNA is unchanged. This antiviral effect is triggered by interferon and tumor necrosis factor that are induced in the liver following hepatectomy and either prevent the formation or accelerate the degradation of viral nucleocapsids in the cytoplasm of the hepatocyte. Despite massive hepatocellular turnover, this effect is independent of liver cell division, indicating that HBV replicates efficiently in resting and dividing hepatocytes.     

Interleukin-12 inhibits hepatitis B virus replication in transgenic mice.

Interleukin-12 (IL-12) is a heterodimeric cytokine produced by antigen-presenting cells that has the ability to induce gamma interferon (IFN-gamma) secretion by T and natural killer cells and to generate normal Th1 responses. These properties suggest that IL-12 may play an important role in the immune response to many viruses, including hepatitis B virus (HBV). Recently, we have shown that HBV-specific cytotoxic T lymphocytes inhibit HBV replication in the livers of transgenic mice by a noncytolytic process that is mediated in part by IFN-gamma. In the current study, we demonstrated that the same antiviral response can be initiated by recombinant murine IL-12 and we showed that the antiviral effect of IL-12 extends to extrahepatic sites such as the kidney. Southern blot analyses revealed the complete disappearance of HBV replicative intermediates from liver and kidney tissues at IL-12 doses that induce little or no inflammation in these tissues. In addition, immunohistochemical analysis demonstrated the disappearance of cytoplasmic hepatitis B core antigen from both tissues after IL-12 treatment, suggesting that IL-12 either prevents the assembly or triggers the degradation of the nucleocapsid particles within which HBV replication occurs. Importantly, we demonstrated that although IFN-gamma, tumor necrosis factor alpha, and IFN-alpha/beta mRNA are induced in the liver and kidney after IL-12 administration, the antiviral effect of IL-12 is mediated principally by its ability to induce IFN-gamma production in this model. These results suggest that IL-12, through its ability to induce IFN-gamma, probably plays an important role in the antiviral immune response to HBV during natural infection. Further, since relatively nontoxic doses of recombinant IL-12 profoundly inhibit HBV replication in the liver and extrahepatic sites in this model, IL-12 may have therapeutic value as an antiviral agent for the treatment of chronic HBV infection.     

Multiple Sclerosis in the Mount Etna Region: Possible Role of Volcanogenic Trace Elements

Background

Trace elements have been hypothesised to be involved in the pathogenesis of Multiple Sclerosis and volcanic degassing is the major natural sources of trace elements. Both incidence of Multiple Sclerosis in Catania and volcanic activity of Mount Etna have been significantly increased during the last 30 years. Due to prevailing trade winds direction, volcanic gases from Etna summit craters are mostly blown towards the eastern and southern sectors of the volcano.

Objective

To evaluate the possible association between Multiple Sclerosis and exposure to volcanogenic trace elements.

Methods

We evaluated prevalence and incidence of Multiple Sclerosis in four communities (47,234 inhabitants) located in the eastern flank and in two communities (52,210 inhabitants) located in the western flank of Mount Etna, respectively the most and least exposed area to crater gas emissions.

Results

A higher prevalence was found in the population of the eastern flank compared to the population of the western one (137.6/100,000 versus 94.3/100,000; p-value 0.04). We found a borderline significantly higher incidence risk during the incidence study period (1980–2009) in the population of the eastern flank 4.6/100,000 (95% CI 3.1–5.9), compared with the western population 3.2/100,000 (95% CI 2.4–4.2) with a RR of 1.41 (95% CI 0.97–2.05; p-value 0.06). Incidence risks have increased over the time in both populations reaching a peak of 6.4/100,000 in the eastern flank and of 4.4/100.000 in the western flank during 2000–2009.

Conclusion

We found a higher prevalence and incidence of Multiple Sclerosis among populations living in the eastern flank of Mount Etna. According to our data a possible role of TE cannot be ruled out as possible co-factor in the MS pathogenesis. However larger epidemiological study are needed to confirm this hypothesis.