Concerted action of the FasL/Fas and perforin/granzyme A and B pathways is mandatory for the development of early viral hepatitis but not for recovery from viral infection

Rescue of in vivo FAS-induced apoptosis of hepatocytes by corticosteroids either associated with alcohol consumption by mice or provided exogenously

The pathogenic effects of many hepatic viral infections are mediated, at least in part, by the immune response to the infected hepatocyte. The immune response in the infected liver involves the interaction of cytotoxic T cells (CTL) with the hepatocytes through the interaction of FAS-ligand on the CTL and FAS on the hepatocyte. The initial hypothesis for this study was that alcohol consumption by mice would sensitize the liver to apoptosis induced by ligation of FAS. C57Bl/6 mice fed ethanol in a liquid diet did show an increased percentage of apoptotic cells 2 h after injection with anti-FAS as compared with the percentage in the control mice. However, 4 and 6 h after anti-FAS injection, control mice showed high percentages of apoptotic cells (20% to 41%) compared with 5% and 4% apoptotic cells in the ethanol-fed mice. The decreased apoptosis of ethanol-fed mice correlated closely with corticosterone levels in the sera. This was confirmed by the finding that adrenalectomized (ADX) mice provided a high level of corticosterone in drinking water were protected against FAS-induced hepatocyte apoptosis. Ethanol-fed mice showed a significant elevation of serum alanine aminotransferase (ALT) levels indicating the development of hepatitis in spite of the relatively low proportion of apoptotic cells in the liver. In conclusion, high levels of corticosterone protect hepatocytes from FAS-mediated apoptosis, but do not prevent the ultimate development of liver damage. In experiments where mice were provided ethanol chronically in drinking water, where stress is minimal, higher levels of ALT were noted in animals in the ethanol group as compared with animals in the control group. These data support the suggestion that ethanol increases hepatocyte sensitivity to FAS-mediated damage.

Suppression of adenoviral gene expression in the liver: role of innate vs adaptive immunity and their cell lysis mechanisms

BACKGROUND

Injection of adenoviral constructs causes liver infection prompting immunity, which suppress viral gene expression. Innate and adaptive immunity mediate these processes raising the question which pathways are the most prominent.

METHODS

Adenovirus expressing the beta-galactosidase (beta-gal) gene was injected into normal and immunodeficient mice. Elimination of beta-gal-expressing hepatocytes and increases in liver enzymes were assayed. Major histocompatibility complex (MHC) class I densities, perforin channel insertion and apoptosis by Fas and tumor necrosis factor (TNF)-alpha were assayed.

RESULTS

At high virus doses, suppression of viral gene expression was as efficient in immunodeficient as in normal mice, while at low doses effects of cytotoxic T lymphocytes (CTL) were demonstrable. Despite CTL priming and elimination of infected hepatocytes no liver injury is detected. Hepatocyte MHC I densities were able to trigger CTL granule exocytosis and perforin lysis in vitro but not in vivo. This is we show is because of decreased sensitivity of hepatocytes from infected mice to perforin and increased sensitivity to Fas and TNF-alpha lysis.

CONCLUSION

Effector cells of the innate immune system are exceedingly effective in suppressing adenoviral gene expression. Perforin-independent pathways, those mediated by TNF-alpha and Fas are very efficient in hepatocytes from virus-infected livers.

Independent roles of perforin, granzymes, and Fas in the control of Friend retrovirus infection

Cytotoxic T-cells (CTL) play a central role in the recovery of mammalian hosts from retroviral infections. However, the molecular pathways that mediate the antiretroviral activity of CTL are still elusive. Here we explore the protective role of the two main cytolytic pathways of CTL, that is, granule exocytosis and Fas/Fas ligand (FasL), in acute and persistent Friend retrovirus (FV) infection of mice. For this purpose, we have used mutant mouse strains with targeted gene defects in one or more components of the two cytolytic pathways including perforin, granzyme A, granzyme B, Fas, and FasL. The important function of CTL in resistance of C57BL/6 (B6) mice to FV is emphasized by the finding that depletion of CD8+ T-cells prior to virus infection resulted in severe splenomegaly and high viral loads in blood and spleen tissue. Analysis of primary FV infection in knockout mice revealed that acute infection was readily controlled in the absence of functional Fas. Most notably in the presence of Fas/FasL each of the three effector molecules of the exocytosis pathway (i.e., perforin, granzyme A, and granzyme B) was capable on its own to mediate suppression of virus replication and protection from leukemia. However, triple knockout mice lacking perforin and the two granzymes were fully susceptible to FV-induced leukemia. In contrast to acute infection the Fas/FasL pathway was mandatory for effective control of FV replication during persistent infection. These findings suggest novel pathways of CTL-mediated viral defense and contribute towards a better understanding of the molecular mechanisms of CTL activity in retroviral infections.

Granzyme B is dispensable for immunologic tolerance to self in a murine model of systemic lupus erythematosus

OBJECTIVE

Proteolytic autoantigen cleavage by the serine protease granzyme B has been implicated in the development of systemic autoimmune disease; however, there has been no conclusive demonstration of a pathogenic role for granzyme B in autoimmunity. In this study, we evaluated the role of granzyme B in a murine model of autoimmunity.

METHODS

To identify potential novel granzyme B substrates, complementary DNAs encoding nuclear factor 45 (NF45) and NF90 were used to generate (35)S-methionine-labeled proteins by coupled in vitro transcription/translation. Radiolabeled proteins were then incubated with purified recombinant granzyme B or caspases, and the cleavage products were analyzed by autoradiography. We also immunized granzyme B-deficient and granzyme B-intact mice with the mineral oil pristane. Production of autoantibodies directed against granzyme B substrates in response to pristane was evaluated by Western blotting, immunoprecipitation, and enzyme-linked immunosorbent assay.

RESULTS

The double-stranded RNA-binding protein NF90 was identified as a novel substrate for caspases and granzyme B, both in vitro and in vivo. NF90 is uniquely cleaved by granzyme B in vitro; however, pristane immunization still induced anti-NF90 antibodies in granzyme B-deficient mice. Pristane-treated granzyme B-deficient mice also produced antibodies directed against the U1-70-kd antigen, a previously identified granzyme B substrate. Last, antibodies directed against U1-70 kd arose spontaneously in granzyme B-deficient mice.

CONCLUSION

These results demonstrate that granzyme B is not required for the production of autoantibodies directed against antigens that are granzyme B substrates in vitro. The data also suggest a protective role for this proapoptotic protease in systemic autoimmunity.

Apoptotic pathways are selectively activated by granzyme A and/or granzyme B in CTL-mediated target cell lysis

Purified cytolytic T lymphocyte (CTL) proteases granzyme (gzm)A and gzmB with sublytic dose of perforin (perf) initiate distinct proapoptotic pathways. Their physiological relevance in CTL-mediated target cell apoptosis is elusive. Using ex vivo virus-immune CD8(+) T cells from mice deficient in perf, gzmA and/or gzmB, and the Fas-resistant EL4.F15 tumor target cell, we show that (a) CTL from gzmA(-/-) or gzmB(-/-) mice similarly induced early proapoptotic features, such as phosphatidyl serine (PS) exposure on plasma membrane, Delta Psi(m) loss, and reactive oxygen radical generation, though with distinct kinetics; (b) CTL from gzmA(-/-) but not from gzmB(-/-) mice activate caspase 3 and 9; (c) PS exposure induced by CTL from gzmA(-/-) or gzmB(-/-) mice is prevented, respectively, by caspase inhibitors or by reactive oxygen scavengers without interfering with target cell death; and (d) all gzm-induced apoptotic features analyzed depend critically on perf. Thus, perf is the principal regulator in CTL-mediated and gzm-facilitated intracellular processes. The ability of gzmA and gzmB to induce multiple independent cell death pathways may be the hosts response to circumvent evasion strategies of pathogens and tumors.

Recent developments in the transcriptional regulation of cytolytic effector cells

Transcription factors have a profound influence on both the differentiation and effector function of cells of the immune system. T-bet controls the cytotoxicity of CD8(+) T cells and the production of interferon-gamma, and it also affects the development and function of natural killer cells and natural killer T cells. Other factors such as eomesodermin, MEF, ETS1 and members of the interferon-regulatory factor family also contribute to the effector function of immune cells. In this review, we focus on recent studies that have shed light on the transcriptional mechanisms that regulate cellular effector function in the immune system.

Perforin and Fas act together in the induction of apoptosis, and both are critical in the clearance of lymphocytic choriomeningitis virus infection

In this report we questioned the current view that the two principal cytotoxic pathways, the exocytosis and the Fas ligand (FasL)/Fas-mediated pathway, have largely nonoverlapping biological roles. For this purpose we have analyzed the response of mice that lack Fas as well as granzyme A (gzmA) and gzmB (FasxgzmAxB(-/-)) to infection with lymphocytic choriomeningitis virus (LCMV). We show that FasxgzmAxB(-/-) mice, in contrast to B6, Fas(-/-), and gzmAxB(-/-) mice, do not recover from a primary infection with LCMV, in spite of the expression of comparable numbers of LCMV-immune and gamma interferon-producing cytotoxic T lymphocytes (CTL) in all mouse strains tested. Ex vivo-derived FasxgzmAxB(-/-) CTL lacked nucleolytic activity and expressed reduced cytolytic activity compared to B6 and Fas(-/-) CTL. Furthermore, virus-immune CTL with functional FasL and perforin (gzmAxB(-/-)) are more potent in causing target cell apoptosis in vitro than those expressing FasL alone (perfxgzmAxB(-/-)). This synergistic effect of perforin on Fas-mediated nucleolysis of target cells is indicated by the fact that, compared to perfxgzmAxB(-/-) CTL, gzmAxB(-/-) CTL induced (i) an accelerated decrease in mitochondrial transmembrane potential, (ii) increased generation of reactive oxygen species, and (iii) accelerated phosphatidylserine exposure on plasma membranes. We conclude that perforin does not mediate recovery from LCMV by itself but plays a vital role in both gzmA/B and FasL/Fas-mediated CTL activities, including apoptosis and control of viral infections.

Can we really learn from model pathogens?

Cytolytic T (Tc) lymphocytes are the first order response of the adaptive immune system in the recovery from primary viral infections. These effector cells execute their function either by direct cytotoxicity through the Fas or perforin pathway and/or by the release of cytokines that either directly or indirectly exert antiviral activity. Mice respond to infection by closely related viruses with a vigorous Tc response, which is characterized by extensive crossreactivity on target cells infected with these viruses. However, the action of these cells can be beneficial, detrimental or neutral. From our current state of knowledge, no generalizations as to protective or detrimental effects of cytolytic effector functions in recovery from virus infections can be made. Thus, virus-host immune interactions have to be assessed individually and cannot be generalized.

Granzymes in cytolytic lymphocytes--to kill a killer?

Granzymes (gzm) are major components of the granules of cytolytic lymphocytes, natural killer and cytotoxic T cells. Their generally accepted mode of action consists of their directed secretion towards a virus-infected or neoplastic target cell and perforin-dependent delivery to the target cell cytosol, where they engage in various actions resulting in target cell apoptosis. Here, based on observations of infection of gzmAxB(-/-) mice with ectromelia virus, mousepox, we propose an additional--and distinct--function for gzmA and B. In this model, gzm constitute one of the first lines of defence of immune cells against virus infection of immune cells themselves. Accordingly, endogenous gzm interfere with viral replication in cytolytic lymphocytes either directly, as a result of their proteolytic activity, leading to destruction of viral proteins, or indirectly, via: (i) processes akin to the caspase cascade when acting as effector molecules in the induction of target cell apoptosis; or (ii) their capacity to induce early inflammatory mediators. We discuss the predictions of the model in the light of available data.

Exocytosis and Fas mediated cytolytic mechanisms exert protection from West Nile virus induced encephalitis in mice

Infection of mice with the flaviviruses West Nile virus (WNV) and Murray Valley encephalitis (MVE) induces cytolytic T-cell responses which are highly cross-reactive on target cells infected with heterologous flaviviruses. Of C57BL/6 mice infected with low doses (10(2)-10(6) PFU) of either virus, 30-40% develop encephalitis and die within 10-12 days. Mice with defects in the Fas or granule exocytosis (perforin and granzymes A and B) pathway of cellular cytotoxicity display reduced mortality and increased survival time when infected with MVE and are protected from encephalitis when deficient in both pathways. This contrasts with infection with WNV where defects in these cytolytic mechanisms increase the percentage of mice that succumb to encephalitis. Thus, no generalizations as to protective or detrimental effects of cytolytic effector functions in recovery from closely related flavivirus infections can be made. Virus-host immune interactions have to be assessed individually and cannot be generalized.

Fatal disseminated mouse adenovirus type 1 infection in mice lacking B cells or Bruton's tyrosine kinase

Mouse adenovirus type 1 (MAV-1) infection of B-cell-deficient and Bruton's tyrosine kinase (Btk)-deficient mice resulted in fatal disseminated disease resembling human adenovirus infections in immunocompromised patients. Mice lacking B cells or Btk were highly susceptible to acute MAV-1 infection, in contrast to controls and mice lacking T cells. To our knowledge, this is the first demonstration that mice with an X-linked immunodeficiency phenotype (Btk deficient) are susceptible to virus-induced disease. Mice lacking B cells or Btk on a C57BL/6 background succumbed with encephalomyelitis, hepatitis, and lymphoid necrosis. Mice lacking B cells on a BALB/c background succumbed with enteritis and hepatitis. Survival of acute MAV-1 infection correlated with early T-cell-independent neutralizing antibody and T-cell-independent antiviral immunoglobulin M. Treatment of MAV-1-infected Btk(-/-) mice 4 to 9 days postinfection with antiserum harvested 6 to 9 days postinfection from MAV-1-infected Btk(+/+) mice was therapeutic. Our findings implicate a critical role for B-cell function in preventing disseminated MAV-1 infection, particularly production of early T-cell-independent antiviral immunoglobulin M.

Granzyme B: pro-apoptotic, antiviral and antitumor functions

Granzyme B is a caspase-like serine protease that is released by cytotoxic lymphocytes to kill virus-infected and tumor cells. Major recent advances in our understanding of granzyme B biochemistry, biology and function include an appreciation of its uptake into and trafficking within target cells, a thorough dissection of how cell death is triggered, and the identification of the serpin protease inhibitor PI-9, which regulates its function in lymphocytes and in other cells. The roles that granzyme B plays in human pathologies, such as transplant rejection, viral immunity and particularly tumor immune surveillance, remain a topic for vigorous debate and conjecture. The recent discovery of a triply mutated human granzyme B allele, whose product is predicted to possess a reduced capacity to induce cell death, opens the way for major progress in these areas in coming years.

IFN-gamma promotes Fas ligand- and perforin-mediated liver cell destruction by cytotoxic CD8 T cells

To study liver cell damage by CTL, CD8 T cells from P14 TCR transgenic (tg) mice specific for the gp33 epitope of lymphocytic choriomeningitis virus with either deficiency in IFN-gamma (P14.IFN-gamma(null)), functional Fas ligand (P14.gld), or perforin (P14.PKO) were transferred into H8 tg mice ubiquitously expressing gp33 Ag. Treatment of H8 recipient mice with agonistic anti-CD40 Abs induced vigorous expansion of the transferred P14 T cells and led to liver cell destruction determined by increase of glutamate dehydrogenase serum levels and induction of caspase-3 in hepatocytes. Liver injury was mediated by the Fas/Fas ligand (FasL) pathway and by perforin, because P14.gld and P14.PKO T cells failed to induce increased glutamate dehydrogenase levels despite strong in vivo proliferation. In addition, H8 tg mice lacking Fas were resistant to the pathogenic effect of P14 T cells. Besides FasL and perforin, IFN-gamma was also required for liver cell damage, because P14.IFN-gamma(null) T cells adoptively transferred into H8 mice failed to induce disease. Moreover, Fas expression on hepatocytes from H8 recipient mice was increased after transfer of wild-type compared with P14.IFN-gamma(null) T cells, and wild-type P14 T cells expressed higher levels of FasL than P14 T cells lacking IFN-gamma. Thus, our data suggest that IFN-gamma released by activated CD8 T cells upon Ag contact facilitates liver cell destruction.

Expression of FasL and perforin/granzyme B mRNA in chronic hepatitis B virus infection

Cytotoxic T lymphocytes are essential components of immune responses during chronic hepatitis B (CHB). It has been known that Fas ligand (FasL) and perforin/granzyme B-based mechanisms account for all T cell-mediated cytotoxicity. In the present work, we examined the correlation between injury of the hepatocytes and mRNA expression of FasL and perforin/granzyme B in liver tissue to investigate the roles of both the FasL and the perforin/granzyme B pathways in CHB. Reverse transcription-polymerase chain reaction was used to identify intrahepatic expression of FasL and perforin/granzyme B in liver biopsy specimens from 24 patients with hepatitis B virus (HBV) infection. In addition, the transferase-mediated deoxyuridine triphosphate nick end-labelling (TUNEL) method was used to determine the degree of apoptosis. The degree of mRNA expression and apoptosis were compared with the histologic activity index (HAI) and serology, including alanine aminotransferase (ALT). Intrahepatic mRNA expression rates of FasL, perforin and granzyme B were seen in 79.2, 62.5 and 33.3% of patients, respectively, and correlated with ALT levels (P < 0.05). Intrahepatic expression of FasL and perforin mRNA were significantly correlated with HAI (P < 0.05). Also, apoptosis documented by the TUNEL assay was correlated with HAI and intrahepatic mRNA expression of FasL and perforin (P < 0.05). Our results show that the T-cell mediated perforin death pathway as well as the Fas system play important roles in liver cell injury in HBV infection and that apoptosis mediated by the Fas/FasL system is closely correlated with HAI in chronic HBV infection.

Cell-mediated cytotoxicity in recovery from poxvirus infections

The availability of mutant and gene targeted knockout mice with defects in components of cellular cytotoxicity mediated by either the Fas or the exocytosis pathway permitted an analysis of their role in recovery from poxvirus infections. Ectromelia (EV), a natural mouse pathogen causing mousepox, the closely related orthopoxviruses cow pox (CPV) and vaccinia virus (VV), each encode serpins that inhibit Fas mediated apoptosis and lysis of target cells. Nevertheless, distinct differences were seen when the three viruses were inoculated into perforin-deficient mice: highly resistant C57Bl/6 mice became susceptible to low doses of EV; resistance to CPV increased whereas there was no effect on VV infections. Absence of the cytolytic granule associated granzymes (gzm) A and B rendered C57Bl/6 mice increasingly more susceptible to EV infections. Lack of both gzms rendered them as susceptible as perforin deficient mice, despite the presence of functionally active perforin. Elevated EV titres in liver and spleen of gzmA x B deficient mice, early after infection and before cytotoxic T cells were detectable, strongly suggests that these two gzms exert an antiviral effect by a mechanism distinct from effector molecules of NK and cytotoxic T cells.

The ABCs of granule-mediated cytotoxicity: new weapons in the arsenal

Granule exocytosis is the main pathway for the immune elimination of virus-infected cells and tumour cells by cytotoxic T lymphocytes and natural killer cells. After target-cell recognition, release of the cytotoxic granule contents into the immunological synapse formed between the killer cell and its target induces apoptosis. The granules contain two membrane-perturbing proteins, perforin and granulysin, and a family of serine proteases known as granzymes, complexed with the proteoglycan serglycin. In this review, I discuss recent insights into the mechanisms of granule-mediated cytotoxicity, focusing on how granzymes A, B and C and granulysin activate cell death through caspase-independent pathways.

Control of lymphocytic choriomeningitis virus infection in granzyme B deficient mice

We have investigated whether granzyme B (GzmB) is required for effective cytotoxic T lymphocyte (CTL) mediated control of lymphocytic choriomeningitis virus (LCMV) infection. Clearance of LCMV from tissues of GzmB-deficient (GzmB-) mice following intraperitoneal infection with LCMV was impaired compared with control mice; however, the virus was ultimately eliminated. The impaired clearance of LCMV in GzmB- mice was not due to a deficiency in the generation of LCMV-specific T cells. In addition, CTL from LCMV-infected GzmB- mice efficiently lysed virus-infected cells in vitro, but were deficient in their ability to induce rapid DNA fragmentation in target cells. We examined whether the development of protective immunity against intracranial (i.c.) rechallenge with LCMV was compromised in GzmB- mice. We found that clearance of LCMV from the brain following secondary i.c. infection also was slower in the absence of GzmB; however, the virus was ultimately eliminated and the mice survived. Our data indicate that clearance of LCMV is delayed in the absence of GzmB expression, but that other CTL effector molecules can compensate for the absence of this granule constituent in vivo.

Functional significance of the perforin/granzyme cell death pathway

Perforin/granzyme-induced apoptosis is the main pathway used by cytotoxic lymphocytes to eliminate virus-infected or transformed cells. Studies in gene-disrupted mice indicate that perforin is vital for cytotoxic effector function; it has an indispensable, but undefined, role in granzyme-mediated apoptosis. Despite its vital importance, the molecular and cellular functions of perforin and the basis of perforin and granzyme synergy remain poorly understood. The purpose of this review is to evaluate critically recent findings on cytotoxic granule-mediated cell death and to assess the functional significance of postulated cell-death pathways in appropriate pathophysiological contexts, including virus infection and susceptibility to experimental or spontaneous tumorigenesis.

Quantitative detection of T-cell activation markers by real-time PCR in renal transplant rejection and correlation with histopathologic evaluation

BACKGROUND

The quest for noninvasive methods to diagnose rejection in solid-organ transplants has been rejuvenated by recent observations that specific cytotoxic T-cell markers are up-regulated during rejection.

METHODS

We developed a one-step real-time polymerase chain reaction (PCR) method allowing reliable detection of the expression of several T-cell genes within a relatively short period of time. The assay is highly sensitive and reproducible with a wide dynamic range allowing accurate quantification of target mRNA in as little as 3 pg total RNA. The utility of this assay in detecting renal allograft rejection was evaluated. Peripheral blood mononuclear cells were collected from 27 patients undergoing kidney allograft biopsies for renal dysfunction after transplantation. Expression of the T-cell activation markers, granzyme B, perforin, and HLA-DRA, was quantified and correlated to the histopathologic changes in the renal biopsies.

RESULTS

In cases with allograft rejection (n=8), peripheral lymphocyte expression was increased for granzyme B (P <0.001) and perforin (P <0.08) compared with cases without rejection (n=19). Granzyme B mRNA up-regulation showed the highest specificity for detecting rejection (95%). Moreover, HLA-DRA mRNA was significantly up-regulated (P <0.0016) and had the highest sensitivity (88%) detecting rejection. The up-regulation of both granzyme B and HLA-DRA was most specific in detecting rejection, P<0.001.

CONCLUSIONS

These data demonstrate that a rapid test of target gene up-regulation using real-time PCR can be used as an aid in the diagnosis of kidney allograft rejection. This is also the first report on the possible utility of HLA-DRA mRNA up-regulation as a marker for kidney transplant rejection.

Antigen-dependent release of IFN-gamma by cytotoxic T cells up-regulates Fas on target cells and facilitates exocytosis-independent specific target cell lysis

Effector cytolytic T (Tc) lymphocytes, deficient in the exocytosis-mediated pathway of target cell lysis, induce Fas on target cells and, in turn, delayed cell death and apoptosis via the Fas ligand-Fas interaction. The induction of Fas can be blocked by anti- IFN-gamma Abs. This Fas up-regulation on initially Fas-negative target cells is not mediated by TCR-MHC/peptide signaling per se, but by secreted IFN-gamma from Tc cells after Ag engagement. The Fas up-regulation by Tc cells can be mimicked by treatment of target cells with rIFN-gamma. Tc cells from IFN-gamma knockout mice do not induce Fas expression on target cells. Tc cell-mediated Fas expression on third party, bystander, target cells does not enhance their susceptibility to lysis by these nominal effector cells. The results are discussed as to the possible relevance of the phenomenon in efficiency and regulation of the Tc cell response to infections by viruses.

Role of activated CD8+ T cells in the initiation and continuation of hepatic damage

The cause of alcoholic liver disease (ALD) is multifactorial and poorly understood. It is clear that alcohol alone is not responsible for most of the changes associated with ALD and that cofactors are involved in initiation and production of ALD. One cofactor that has received a great deal of attention recently is the concomitant infection with hepatitis C virus (HCV) and alcohol abuse. The interactive effects of HCV and alcohol abuse are still unclear, but apparently they are the result of an inability of the immune system to control the viral infection and exaggerated hepatocyte damage mediated by either the cells of the inflammatory response or factors produced by the inflammatory cells. This review will focus on one aspect of the possible pathogenic effects associated with alcohol abuse and HCV infection: the possible role of the immune system, notably the cytotoxic T lymphocyte (CTL) response. It is clear that the development of a CTL response is critical for the control of HCV infections, and it is also likely that this response is involved in liver damage. In this review, the evidence that shows the importance of the CD8(+) CTL in viral clearance and the role for pathogenesis will be presented. Findings obtained from animal studies that support the suggestion that activated CD8(+) CTLs can induce liver damage will be presented, as will results of recent studies from my laboratory that provide evidence for an effect of alcohol to enhance the liver damage mediated by activated CD8(+) T cells.