Mechanisms inducing or controlling CD8+ T cell responses against self- or non-self-antigens

Hepatitis C virus core protein impairs in vitro priming of specific T cell responses by dendritic cells and hepatocytes

BACKGROUND/AIMS

Hepatitis C virus leads to chronic hepatitis in the majority of infected individuals. The mechanism of viral persistence is not completely understood. Hepatitis C virus core protein is produced within hepatocytes and is secreted during HCV infection. Our study characterizes the effects of core protein on T cell priming in mice.

METHODS

We used a system of antigen-specific in vitro priming of CD4(+) and CD8(+) T cells by myeloid dendritic cells, hepatoma cells or primary hepatocytes. Core protein was either added to the cultures or expressed by antigen-presenting cells.

RESULTS

Antigen-presenting cells treated with core protein showed reduced surface expression of major histocompatibility molecules. Myeloid dendritic cells showed also reduced expression of costimulatory molecules. CD4(+) and CD8(+) T cells primed by these cells showed defects in activation, proliferation, and cytokine production. Importantly, CD4(+) and also CD8(+) T cells primed in the presence of core protein showed an increase in interleukin-10 production resembling the phenotype of regulatory T cells.

CONCLUSIONS

Hepatitis C virus core protein inhibits priming of antigen-specific CD4(+) and CD8(+) T cell responses by downregulation of major histocompatibility molecules and costimulatory molecules on antigen-presenting cells and induces development of IL-10-producing T cells.

Molecular mimicry, bystander activation, or viral persistence: infections and autoimmune disease

Virus infections and autoimmune disease have long been linked. These infections often precede the occurrence of inflammation in the target organ. Several mechanisms often used to explain the association of autoimmunity and virus infection are molecular mimicry, bystander activation (with or without epitope spreading), and viral persistence. These mechanisms have been used separately or in various combinations to account for the immunopathology observed at the site of infection and/or sites of autoimmune disease, such as the brain, heart, and pancreas. These mechanisms are discussed in the context of multiple sclerosis, myocarditis, and diabetes, three immune-medicated diseases often linked with virus infections.

Neue Erkenntnis zur Rasmussen-Enzephalitis

Rasmussen encephalitis (RE) is a severe and at the same time pathophysiologically fascinating condition. The chronic inflammation affects one of the two cerebral hemispheres and destroys it during the disease process that lasts from months to years. The patients -- mostly children -- suffer from frequent pharmacoresistant seizures, often in the form of epilepsia partialis continua. In parallel to the atrophy of the affected hemisphere, the neurological functions associated with it decline continuously. This results in a final stage with a usually high-grade sensorimotor hemisyndrome, hemianopia, cognitive impairment and -- if the language-dominant hemisphere is affected -- aphasia. Research results in the last 5 years have contributed to a deeper understanding of the pathogenesis of this condition. Formal diagnostic criteria have been proposed, and new therapeutic options have emerged by which the disease progression can be slowed or stopped. This article summarizes the current research results on the background of older data and gives recommendations regarding diagnostic and therapeutic procedures in RE patients.

HIV‐1 Nef equips dendritic cells to reduce survival and function of CD8 + T cells: a mechanism of immune evasion

The accessory HIV-1 Nef protein is a crucial determinant for viral replication and pathogenesis. During HIV infection, loss of immune control in the setting of a strong and broad HIV-specific T-lymphocyte response, leads to a lethal outcome through AIDS. Moreover, dysfunction of dendritic cells (DCs) may contribute to the immune suppression associated with AIDS progression. We recently demonstrated that exogenous Nef selectively activates immature DCs manipulating their phenotypical, morphological, and functional developmental program. Here, we tracked whether Nef, targeting DCs, could be involved in the dysregulation of CD8+ T cell responses. We found that Nef inhibits the capacity of DCs to prime alloreactive CD8+ T cell responses down-regulating their proliferation and functional competence. This coincides with the induction of CD8+ T cell apoptosis. Nef oversees apoptotic killing of CD8+ T cells up-regulating TNF-alpha and FasL production by DCs and interfering with the death receptor pathway in CD8+ T cells and thus activating caspase 8. Our findings suggest that Nef may contribute to the immune evasion associated with HIV-1 infection, subverting DC biology. This may help explain the pleiotropic function that Nef plays during infection and makes this protein an attractive target for preventive and therapeutic intervention.