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Blood, 1 December 2007, Vol. 110, No. 12, pp. 3949-3958. Prepublished online as a Blood First Edition Paper on August 15, 2007; DOI 10.1182/blood-2007-05-092189.
IMMUNOBIOLOGY Friend retrovirus infection of myeloid dendritic cells impairs maturation, prolongs contact to naïve T cells, and favors expansion of regulatory T cells1 Department of Dermatology, University of Muenster, Muenster; 2 Institute for Virology and 3 Institute of Pathology and Neuropathology, University Duisburg-Essen, Essen; and 4 Department of Dermatology, University of Mainz, Mainz, Germany Retroviruses have developed immunmodulatory mechanisms to avoid being attacked by the immune system. The mechanisms of this retrovirus-associated immune suppression are far from clarified. Dendritic cells (DCs) have been attributed a decisive role in these pathogenic processes. We have used the Friend retrovirus (FV) mouse model in order to acquire further knowledge about the role of infection of DCs in virus-induced immunosuppression. About 20% of the myeloid DCs that were generated from the bone marrow of FV-infected mice carried FV proteins. The infection was productive, and infected DCs transmitted the virus in cell culture and in vivo. FV infection of DCs led to a defect in DC maturation, as infected cells expressed very little costimulatory molecules. Live imaging analysis of the cell contact between DCs and T cells revealed prolonged contacts of T cells with infected DCs compared with uninfected DCs. Although naive T cells were still activated by FV-infected DCs, this activation did not result in antigen-specific T-cell proliferation. Interestingly, infected DCs expanded a population of Foxp3+ regulatory T cells with immunosuppressive potential, suggesting that the contact between naive T cells and retrovirus-infected DCs results in tolerance rather than immunity. Thus, retroviral infection of DCs leads to an expansion of regulatory T cells, which might serve as an immune escape mechanism of the virus.
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