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Infection and Immunity, September 2002, p. 5167-5176, Vol. 70, No. 9
0019-9567/02/$04.00+0 DOI: 10.1128/IAI.70.9.5167-5176.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Department of Microbiology,1 Department of Bioregulation, Leprosy Research Center, National Institute of Infectious Diseases, Higashimurayama,3 Department of Pathology, Tokyo Women's Medical University, Shinjuku, Tokyo, Japan2
Received 20 February 2002/ Returned for modification 8 April 2002/ Accepted 31 May 2002
Host defense against Mycobacterium leprae infection is chiefly mediated by gamma interferon (IFN-
)-secreting cytotoxic T cells. Since which antigen-presenting cell populations act to stimulate these T cells is not fully understood, we addressed the role of monocyte-derived dendritic cells (DCs). The DCs phagocytosed M. leprae and expressed bacterially derived antigens (Ags), such as phenolic glycolipid 1 (PGL-1), in the cytoplasm, as well as on the cell surface. The expression of HLA-ABC and -DR Ags on DCs was down-regulated by M. leprae infection, and that of CD86 was up-regulated, but not as fully as by Mycobacterium bovis BCG infection. Induction of CD83 expression required a large number of M. leprae cells. When a multiplicity of infection of >40 was used, the DCs induced a significant proliferative and IFN-
-producing response in autologous T cells. However, these responses were significantly lower than those induced by BCG- or Mycobacterium avium-infected DCs. A CD40-mediated signaling in M. leprae-infected DCs up-regulated the expression of HLA Ags, CD86, and CD83 but did not enhance T-cell-stimulating ability. Therefore, M. leprae-infected DCs are less efficient at inducing T-cell responses. However, when the surface PGL-1 on M. leprae-infected DCs was masked by a monoclonal antibody, the DCs induced enhanced responses in both CD4+- and CD8+-T-cell subsets. M. leprae is a unique pathogen which remains resistant to DC-mediated T-cell immunity, at least in the early stages of infection.
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