Relationship of specific MRI findings to treatment outcomes in patients receiving transforaminal epidural steroid injections

OBJECTIVES

To determine whether specific MRI findings are related to outcomes after lumbar transforaminal epidural steroid injections (TFESI) and to assess the inter-rater reliability of imaging diagnosis.

MATERIALS AND METHODS

A prospective outcomes study on 156 consecutive patients with 1-month follow-up outcomes data and MRI within 3 months of TFESI was conducted. Pain levels (numerical rating scale) (NRS) were recorded prior to injection. Overall 'improvement' was determined using the Patients Global Impression of Change (PGIC) scale and NRS data were collected at three time points post injection. Two radiologists independently evaluated all images blinded to treatment outcome for reliability of diagnosis. The Chi-square test compared MRI findings for the senior radiologist to 'improvement'. NRS change scores were compared to MRI findings with the unpaired t-test or ANOVA. Kappa and percent agreement assessed inter-rater agreement of diagnosis.

RESULTS

The only abnormality linked to 'improvement' (p = 0.03) and higher NRS change scores (p = 0.0001) at 1 month was the disc herniation morphology 'protrusion + sequestration'. Patients with degeneration by osteophytes (p = 0.034), grade 3 foraminal nerve root compression (p = 0.01) and foraminal/extraforaminal location of herniation (p = 0.014) also had higher 1 month NRS change scores. Reliability of diagnosis was 'fair' to 'substantial' depending on MRI findings.

CONCLUSIONS

Patients with disc protrusion plus sequestration were significantly more likely to report overall improvement and more pain reduction at 1 month. Higher pain reduction was noted in patients with degeneration by osteophytes, grade 3 foraminal nerve root compression, or foraminal/extraforaminal disc herniation location.

Thymic stromal lymphopoietin deficiency attenuates experimental autoimmune encephalomyelitis

In the present study we examined the role of thymic stromal lymphopoietin (TSLP) in experimental autoimmune encephalomyelitis (EAE). Here, we report that TSLP knock-out (KO) mice display a delayed onset of disease and an attenuated form of EAE. This delayed onset was accompanied by a reduced number of encephalitogenic T helper type 1 (Th1) cells in the central nervous system (CNS) of TSLP KO mice. In addition, CD4(+) and CD8(+) T cells from CNS of TSLP KO mice show a reduced activation status in comparison to wild-type mice. It is noteworthy that we could also show that lymph node cells from TSLP KO mice expanded less efficiently and that interleukin (IL)-6-, interferon (IFN)-γ and tumour necrosis factor (TNF)-α levels were reduced. Furthermore, CD3(+) T cells isolated in the preclinical phase from myelin oligodendrocyte glycoprotein peptide 35-55 (MOG(35-55))-immunized TSLP KO mice showed a reduced response after secondary exposure to MOG(35-55), indicating that differentiation of naive T cells into MOG(35-55)-specific effector and memory T cells was impaired in KO mice. The addition of recombinant TSLP enhanced T cell proliferation during MOG(35-55) restimulation, showing that T cells also respond directly to TSLP. In summary, these data demonstrate that expression of, and immune activation by, TSLP contributes significantly to the immunopathology of EAE.

Soluble CD83 ameliorates experimental colitis in mice

The physiological balance between pro- and anti-inflammatory processes is dysregulated in inflammatory bowel diseases (IBD) as in Crohn's disease and ulcerative colitis. Conventional therapy uses anti-inflammatory and immunosuppressive corticosteroids to treat acute-phase symptoms. However, low remission rate and strong side effects of these therapies are not satisfying. Thus, there is a high medical need for new therapeutic strategies. Soluble CD83, the extracellular domain of the transmembrane CD83 molecule, has been reported to have interesting therapeutic and immunosuppressive properties by suppressing dendritic cell (DC)-mediated T-cell activation and inducing tolerogenic DCs. However, the expression and function of CD83 in IBD is still unknown. Here, we show that CD83 expression is upregulated by different leukocyte populations in a chemical-induced murine colitis model. Furthermore, in this study the potential of sCD83 to modulate colitis using an experimental murine colitis model was investigated. Strikingly, sCD83 ameliorated the clinical disease symptoms, drastically reduced mortality, and strongly decreased inflammatory cytokine expression in mesenteric lymph nodes and colon. The infiltration of macrophages and granulocytes into colonic tissues was vigorously inhibited. Mechanistically, we could show that sCD83-induced expression of indolamine 2,3-dioxygenase is essential for its protective effects.

Symptomatic magnetic resonance imaging-confirmed lumbar disk herniation patients: a comparative effectiveness prospective observational study of 2 age- and sex-matched cohorts treated with either high-velocity, low-amplitude spinal manipulative therapy or imaging-guided lumbar nerve root injections

OBJECTIVES

The purpose of this study was to compare self-reported pain and "improvement" of patients with symptomatic, magnetic resonance imaging-confirmed, lumbar disk herniations treated with either high-velocity, low-amplitude spinal manipulative therapy (SMT) or nerve root injections (NRI).

METHODS

This prospective cohort comparative effectiveness study included 102 age- and sex-matched patients treated with either NRI or SMT. Numerical rating scale (NRS) pain data were collected before treatment. One month after treatment, current NRS pain levels and overall improvement assessed using the Patient Global Impression of Change scale were recorded. The proportion of patients, "improved" or "worse," was calculated for each treatment. Comparison of pretreatment and 1-month NRS scores used the paired t test. Numerical rating scale and NRS change scores for the 2 groups were compared using the unpaired t test. The groups were also compared for "improvement" using the χ(2) test. Odds ratios with 95% confidence intervals were calculated. Average direct procedure costs for each treatment were calculated.

RESULTS

No significant differences for self-reported pain or improvement were found between the 2 groups. "Improvement" was reported in 76.5% of SMT patients and in 62.7% of the NRI group. Both groups reported significantly reduced NRS scores at 1 month (P = .0001). Average cost for treatment with SMT was Swiss Francs 533.77 (US $558.75) and Swiss Francs 697 (US $729.61) for NRI.

CONCLUSIONS

Most SMT and NRI patients with radicular low back pain and magnetic resonance imaging-confirmed disk herniation matching symptomatic presentation reported significant and clinically relevant reduction in self-reported pain level and increased global perception of improvement. There were no significant differences in outcomes between NRI and SMT. When considering direct procedure costs, the average cost of SMT was slightly less expensive.

The interaction between dendritic cells and herpes simplex virus-1

Dendritic cells (DCs) are the most potent antigen-presenting cells, because they are also able to induce native T cells. Thus they are crucial in the induction of antiviral immune responses. Several viral immune escape mechanisms have been described; here we concentrate on the interaction between DCs and herpes simplex virus type 1 (HSV-1). DCs can be infected by HSV-1; however, only immature DCs generate infectious viral particles, whereas mature DCs do not support virus production and only immediate-early and early viral transcripts are generated. To induce potent immune responses DCs must mature. Interestingly, HSV-1 interferes with this maturation process, thus inhibiting antiviral T cell stimulation. Furthermore, HSV-1 strongly interferes with DC-mediated T cell proliferation. A striking finding was the complete degradation of CD83, the best-known marker for mature DC, after HSV-1 infection in lysosomal compartments. This CD83 degradation coincided with a clearly reduced T cell stimulation representing an additional new escape strategy. The functional role and the importance of CD83 are discussed in detail.

The extracellular domain of CD83 inhibits dendritic cell-mediated T cell stimulation and binds to a ligand on dendritic cells

CD83 is an immunoglobulin (Ig) superfamily member that is upregulated during the maturation of dendritic cells (DCs). It has been widely used as a marker for mature DCs, but its function is still unknown. To approach its potential functional role, we have expressed the extracellular Ig domain of human CD83 (hCD83ext) as a soluble protein. Using this tool we could show that immature as well as mature DCs bind to CD83. Since CD83 binds a ligand also expressed on immature DCs, which do not express CD83, indicates that binding is not a homophilic interaction. In addition we demonstrate that hCD83ext interferes with DC maturation downmodulating the expression of CD80 and CD83, while no phenotypical effects were observed on T cells. Finally, we show that hCD83ext inhibits DC-dependent allogeneic and peptide-specific T cell proliferation in a concentration dependent manner in vitro. This is the first report regarding functional aspects of CD83 and the binding of CD83 to DCs.

Genetic immunization of wild-type and hepatitis C virus transgenic mice reveals a hierarchy of cellular immune response and tolerance induction against hepatitis C virus structural proteins

To study the effect of genetic immunization on transgenic expression of hepatitis C virus (HCV) proteins, we evaluated the immunological response of HCV transgenic mice to HCV expression plasmids. FVB/n transgenic mice expressing HCV structural proteins (core, E1, and E2) and wild-type (WT) FVB/n mice were immunized intramuscularly with plasmids expressing core (pHCVcore) or core/E1/E2 (pHCVSt). After immunization, HCV-specific humoral and cellular immune response was studied. Both WT and transgenic mice immunized with either HCV construct produced antibodies and exhibited T-cell proliferative responses against core or envelope. In WT mice immunized with pHCVSt, cytotoxic T-lymphocyte (CTL) activities were detected against E2 but not against core or E1, whereas strong CTL activities against core could be detected in WT mice immunized with pHCVcore. In pHCVSt-immunized, transgenic mice, CTL activities against the core or envelope were completely absent, but core-specific CTL activities could be detected in pHCVcore-immunized transgenic mice. A similar pattern of immune responses was also observed in other mouse strains, including a transgenic line expressing human HLA-A2.1 molecules (AAD mice). Despite the presence of a peripheral cellular immunity against HCV, no liver pathology or lymphocytic infiltrate was observed in these transgenic mice. Our study suggests a hierarchy of CTL response against the HCV structural proteins (E2 > core > E1) in vivo when the proteins are expressed as a polyprotein. The HCV transgenic mice can be induced by DNA immunization to generate anti-HCV antibodies and anticore CTLs. However, they are tolerant at the CTL level against the E2 protein despite DNA immunization.

Hepatitis C virus-like particles induce virus-specific humoral and cellular immune responses in mice

We have recently described the production of hepatitis C virus-like particles (HCV-LPs) in insect cells that resemble the putative virions. Here we evaluate the humoral and cellular immunogenicity of the virus-like particles with or without viral p7 protein, a small viral polypeptide that resides between the structural and nonstructural regions of the HCV polyprotein and whose function has not been defined. Immunized BALB/c mice developed high titers of anti-E2 antibodies and virus-specific cellular immune responses including cytotoxic T lymphocytes and T helper responses with gamma interferon production. The virus-like particles without p7 generated a higher cellular immune response with a more T(H)1 profile than the particles with p7. Immunization of heat-denatured particles resulted in substantially lower humoral and cellular responses, suggesting that the immunogenicity is strongly dependent on particle formation. Administration of CpG oligonucleotide or cationic lipid 3beta-[N-(N',N'-dimethylaminoethane)carbamoyl]cholesterol (DC-Chol), two potent adjuvants, did not significantly enhance the immunogenicity of HCV-LPs. Our results indicate that HCV-LPs can induce humoral and cellular immune responses and offer a promising approach to vaccine development.

Vaccine development for hepatitis C

Given the global disease burden and public health impact of hepatitis C, the development of an effective vaccine is of paramount importance. However, many challenging obstacles loom ahead of this goal. The hepatitis C virus (HCV), being an RNA virus, can mutate rapidly in adaptation to the environment, thus contributing to the high sequence divergence of multiple viral isolates in the world. The highest heterogeneity has been found in the hypervariable region of the envelope glycoprotein 2, which contains a principal neutralization epitope. HCV also causes persistent infection in a high percentage of immunocompetent hosts despite active immune response. The lack of an efficient tissue culture system for propagating HCV and testing neutralizing antibodies adds further complexity to the task of vaccine development. The immunologic correlates associated with disease progression or protection are yet to be defined, but recent studies suggest that a vigorous multispecific cellular immune response is important in the resolution of infection. Induction of high-titer, long-lasting, and cross-reactive antienvelope antibodies and a vigorous multispecific cellular immune response that includes both helper and cytotoxic T lymphocytes may be necessary for an effective vaccine. Several promising approaches have been used to develop an HCV vaccine. Novel vaccine candidates based on molecular technology such as recombinant proteins, peptides, viruslike particles, naked DNA, and recombinant viruses are being explored. The final vaccine product may require multiple components that target various aspects of protective immunity. Finally, sterilizing immunity may not be necessary if a vaccine can be developed to prevent chronic infection, which is the major cause of morbidity and mortality from this disease.

A hepatitis C virus (HCV) core protein derived peptide inhibits HCV specific lymphocyte proliferation

T helper lymphocytes are important regulatory cells for the immune response in chronic hepatitis C. They recognize peptides, which are generated from the viral proteins by antigen processing and are bound to MHC (major histocompatibility complex) class II molecules. However, antigen processing might also result in non-immunogenic peptide fragments that can modify T cell activation. - To identify such peptide fragments in hepatitis C, we studied binding of 15 synthetic HCV core derived peptides to MHC class II molecules of 9 human homozygous typing B cell lines (HT-BCLs) as well as T cell proliferation in 41 HLA-typed patients with chronic hepatitis C. - We identified a peptide (HCV core aa 59-83) which bound to 7 HT-BCLs, whereas PBMC of only 2 out of 36 patients with the corresponding HLA-DR alleles proliferated in response to this peptide. Competition experiments indicated that small amounts of peptide aa 59-83 specifically inhibited the proliferative response to the recombinant core protein but not to core derived immunogenic peptides. Our data show that a peptide fragment from the HCV core region aa 59-83 can interfere in vitro with immune recognition of the HCV core protein.

Hepatitis C virus-like particles synthesized in insect cells as a potential vaccine candidate

BACKGROUND & AIMS

Hepatitis C virus (HCV) is a leading cause of chronic hepatitis in the world. Successful vaccine development is crucial in controlling global HCV infection. We have previously described the generation of HCV-like particles (HCV-LPs) in insect cells using a recombinant baculovirus containing the complementary DNA of the HCV structural proteins. These HCV-LPs had similar morphological and biophysical properties as the putative virions. In this study, we analyzed the structural features, antigenic composition, seroreactivity, and immunogenicity of purified HCV-LPs.

METHODS

HCV-LPs were analyzed by electron microscopy and antibody immunolabeling and precipitation. An enzyme-linked immunosorbent assay (ELISA) using HCV-LPs was developed. The humoral response to HCV-LPs in mice was studies by core and envelope ELISAs, Western immunoblotting, and immunofluorescence.

RESULTS

Structural and antigenic compositions of HCV-LPs were shown to be similar to those of putative HCV virions. Using the HCV-LP ELISA, high-titer anti-HCV antibodies were detected in individuals infected with various HCV genotypes. In vivo, HCV-LPs elicited a humoral response broadly directed against HCV structural proteins.

CONCLUSIONS

HCV-LPs resemble HCV virions and are capable of inducing a humoral response targeted against various regions of HCV structural proteins, suggesting that HCV-LPs may be promising as a potential vaccine candidate.

Decreased frequency of HCV core-specific peripheral blood mononuclear cells with type 1 cytokine secretion in chronic hepatitis C

BACKGROUND/AIM

Since the outcome of hepatitis C infection appears to be correlated with the immune response to the HCV core protein, the aim of this study was to investigate the T cell response to hepatitis C virus core and core-derived antigens.

METHODS

As this response may be regulated importantly by differential secretion of cytokines, we determined the number of peripheral blood mononuclear cells (PBMC) that secreted IL-2, IL-4, IL-10, and IFN-gamma in response to a recombinant HCV core protein and a panel of 19 core-derived peptides, using the ELI-Spot-technique. Two groups of patients were studied: group A: 11 patients with previously self-limited HCV infection; group B: 12 patients with chronic hepatitis C.

RESULTS

In group B significantly less IFN-gamma spot forming cells (SFC) could be detected, both after stimulation with the core protein (0.083+/-0.083 SFC vs. 1.3+/-0.4 SFC/10(5) PBMC; p = 0.005 and with the core-derived peptides (1.3+/-0.5 vs. 4.4+/-1.1 SFC SFC/10(5) PBMC; p = 0.007). By analyzing the cytokine response to each single peptide, we found IFN-gamma responses to peptides aa 39-63 and aa 148-172 in group A but not in group B (p<0.03). In group B also, fewer IL-2 secreting cells were found after peptide stimulation (p = 0.04). Whereas subjects of group B showed IL-10-specific responses to HCV peptides more frequently than patients with self-limiting hepatitis C (p = 0.03), the number of IL-4-producing cells was not different between the two groups.

CONCLUSIONS

The data suggest that patients with persistent viremia and chronic liver disease (group B) have less PBMC showing type 1 cytokine (IL-2, IFN-gamma) responses to HCV core protein than patients with self-limited HCV infection (group A).

Increased frequency of the HLA-DR15 (B1*15011) allele in German patients with self-limited hepatitis C virus infection

BACKGROUND

A genetically determined resistance or susceptibility to chronic hepatitis C virus infection (HCV) may make an important contribution to the course of liver disease and may be linked to the human major histocompatibility complex.

DESIGN

Twenty-one subjects with self-limited HCV infection as assessed by the presence of HCV antibodies, absence of HCV-RNA and normal levels of aminotransferases for 2 years were identified from a large pool of blood donors. The frequency of HLA serotypes of these individuals was compared with 49 consecutive patients with chronic hepatitis C.

RESULTS

We detected a significantly higher prevalence of HLA-DR15 in patients with self-limited HCV infection than in patients with chronic hepatitis C (10/21 vs. 6/49; relative risk 6.5; P = 0.02; corrected for multiple comparisons). To confirm HLA assignments by serotyping we also performed sequencing of HLA-DR types in the 27 patients (9 with self-limited infection, 18 with chronic hepatitis C) who had been enrolled during 1995-96. This analysis confirmed the predominance of HLA-DR15 (HLA-DRB1*15011) in self-limited HCV infection (4/9 vs. 1/18; relative risk 13.6; P = 0.03).

CONCLUSIONS

Our data suggest that HLA-DR15 (B1*15011) might constitute an important genetic factor for the elimination of the hepatitis C virus in Germany.

CD30 induction and cytokine profiles in hepatitis C virus core-specific peripheral blood T lymphocytes

Since an efficient control of virus infections may depend on the appropriate lymphokine profile, we studied cytokine responses and CD30 induction, a recently proposed surrogate marker of type 2 cells, in 10 healthy anti-hepatitis C virus (HCV)-seropositive blood donors without viremia (group A) and in 15 patients with hepatitis C (group B). Intracytoplasmic IFN-gamma, IL-2, IL-4, and IL-10 were determined by triple-color flow cytometry in the CD3+ and CD3+/CD30+ lymphocyte subsets after stimulation of PBMC with rHCV core protein and five core-derived peptides corresponding to the four immunodominant Th epitopes C.T1 to C.T4. In group A, more type 1 cytokines were induced by the rHCV core protein and all immunodominant core peptides (p < 0.05), whereas IL-10-producing T cells were found more frequently in group B. Induction of CD30+ T cells was found almost exclusively in group B (p < 0.01). The difference in cytokine responses was due to the CD3+/CD30- T cell subset and not the CD3+/CD30+ subset, which predominantly produced both IL-10 and IFN-gamma, but only small amounts of IL-2 and IL-4. We conclude that immunodominant HCV core peptides induce preferentially type 1 cytokines in healthy anti-HCV-positive blood donors and CD30 expression in patients with chronic hepatitis C. However, in both groups, CD30+ T lymphocytes produce an intermediate Th0-like cytokine profile. Thus, chronicity in HCV infection may reflect a lack of type 1 cytokine production.

CD30 induction and cytokine profiles in hepatitis C virus core-specific peripheral blood T lymphocytes

Since an efficient control of virus infections may depend on the appropriate lymphokine profile, we studied cytokine responses and CD30 induction, a recently proposed surrogate marker of type 2 cells, in 10 healthy anti-hepatitis C virus (HCV)-seropositive blood donors without viremia (group A) and in 15 patients with hepatitis C (group B). Intracytoplasmic IFN-gamma, IL-2, IL-4, and IL-10 were determined by triple-color flow cytometry in the CD3+ and CD3+/CD30+ lymphocyte subsets after stimulation of PBMC with rHCV core protein and five core-derived peptides corresponding to the four immunodominant Th epitopes C.T1 to C.T4. In group A, more type 1 cytokines were induced by the rHCV core protein and all immunodominant core peptides (p &lt; 0.05), whereas IL-10-producing T cells were found more frequently in group B. Induction of CD30+ T cells was found almost exclusively in group B (p &lt; 0.01). The difference in cytokine responses was due to the CD3+/CD30- T cell subset and not the CD3+/CD30+ subset, which predominantly produced both IL-10 and IFN-gamma, but only small amounts of IL-2 and IL-4. We conclude that immunodominant HCV core peptides induce preferentially type 1 cytokines in healthy anti-HCV-positive blood donors and CD30 expression in patients with chronic hepatitis C. However, in both groups, CD30+ T lymphocytes produce an intermediate Th0-like cytokine profile. Thus, chronicity in HCV infection may reflect a lack of type 1 cytokine production.

Anomalous expression of costimulatory molecules B7-1, B7-2 and CD28 in primary biliary cirrhosis

BACKGROUND

T lymphocytes require two important signals for efficient activation: 1) recognition of antigens bound to self major histocompatibility complex antigens, and 2) simultaneous stimulation via so-called costimulatory molecules. Interaction of the costimulatory B7 molecules on antigen presenting cells with CD28 on T lymphocytes appears to be particularly important, as it modifies secretion of cytokines, especially interleukin 2. In primary biliary cirrhosis biliary epithelial cells aberrantly express major histocompatibility complex class II antigens and may function as antigen presenting cells.

METHODS

We studied expression of HLA-DR, B7-1, B7-2 and CD28 on cryostat liver sections in 16 patients with primary biliary cirrhosis, three patients each with autoimmune hepatitis and primary sclerosing cholangitis and nine patients with chronic viral hepatitis (five hepatitis B, four hepatitis C) using mouse monoclonal antibodies in an indirect immunoperoxidase technique.

RESULTS

In advanced primary biliary cirrhosis, HLA-DR was found on 57% of bile ducts, B7-2 on 5% of bile ducts, and B7-1 could not be detected on any bile duct. Neither B7-1 nor B7-2 was seen on bile ducts in the four patients with early primary biliary cirrhosis. HLA-DR+ bile ducts also lacked expression of B7 molecules in autoimmune hepatitis. In contrast, HLA-DR, B7-1 and B7-2 were expressed simultaneously on professional antigen presenting cells such as macrophages in epitheloid granulomas.

CONCLUSION

HLA-DR+ biliary epithelial cells in primary biliary cirrhosis insufficiently co-express B7-1 or B7-2 molecules. Therefore, they must either use different costimulatory molecules, or otherwise are deficient in lymphocyte activation. Since recognition of antigen in the absence of B7-CD28 interaction may lead to anergy of lymphocytes, this might contribute to the impaired cytokine secretion found in primary biliary cirrhosis.

T- and B-cell responses to different hepatitis C virus antigens in patients with chronic hepatitis C infection and in healthy anti-hepatitis C virus--positive blood donors without viremia

As the host's immune response may determine the course of hepatitis C virus (HCV) infection, we studied the humoral and cellular immune responses to HCV-related antigens in subjects with different outcomes of HCV infection. Lymphoproliferative responses and circulating antibodies to a panel of HCV core- and E1-related 25-mer peptides were examined in 10 healthy anti-HCV-seropositive blood donors (group A) and in 29 patients with chronic hepatitis C (group B). In addition, cellular recognition of recombinant HCV proteins (core, NS3, NS4A, NS5A, NS5B) were investigated. In group A, stronger T-cell responses were detected against both HCV proteins (core, P = .03; NS4, P = .005; NS5B, P = .03) and peptides. Proliferation was induced by the same peptides in each group, defining at least five distinctive epitopes within core (amino acids [aa] of 20-44, aa 39-63, aa 79-103, aa 118-152 and aa 148-172) and three regions within E1(aa 198-252, aa 308-372, and aa 368-392). Subjects with strong T-cell responses had low or no detectable levels of peptide-specific antibodies, and vice versa. In particular, T-cell responses were more common in group A; B-cell responses were more common in group B. From our data, we conclude that a benign course of HCV infection may be the consequence of the effective activation of T-helper lymphocytes.

Immune responses in hepatitis C virus infection

Infection with the hepatitis C virus (HCV) commonly causes persistent disease, which may lead to cirrhosis and hepatocellular carcinoma. The pathogenesis of HCV infection is not well understood. It is most likely that both viral and host factors contribute to HCV persistence. This review focuses on the host's immune response to HCV in an attempt to present the current knowledge and concepts of the interactions between the virus and the host during HCV infection. Expansion of B lymphocytes and antibody production to virtually any HCV protein can be detected in most infected patients. However, observations in HCV-infected humans as well as experimental infections in chimpanzees suggest that natural HCV infection does not induce protective immunity, and reinfection can readily be demonstrated after inoculation with homologous or independent strains in HCV-seroconverted animals. Nevertheless, the immune system may gain partial control over HCV even in patients with chronic infection, as HCV infection in severely immunocompromised patients runs a particular cholestatic course which may rapidly lead to death from liver failure. Cytotoxic CD8+ T lymphocyte responses to HCV proteins have been characterized in peripheral blood and liver tissue and were found to be remarkably polyclonal and multispecific. Epitopes were identified on all of the putative HCV proteins, although only few major histocompatibility complex molecules were considered restriction elements. Immunoregulation may be particularly important in HCV infection. The HCV core and NS4 proteins appear to be most immunogenic for peripheral blood lymphocytes, and NS4 specific CD4+ lymphocytes are preferentially compartmentalized to the liver. However, there is an inverse relationship between CD4+ lymphocyte responses and antibody levels in infected patients. Furthermore, a strong cellular response to the HCV core protein apparently favors a benign course of infection. This unusual T-B cell relationship may be the consequence of an altered cytokine release during HCV infection. Alternatively, this virus may have found devices that can disturb immunoregulation in infected patients. A better understanding of these immunological mechanisms induced by HCV infection should make it possible to develop more effective strategies for the prevention and treatment of this insidious disease.