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Correspondence to: Eric G. Pamer, Sections of Infectious Diseases and Immunobiology, Yale University School of Medicine, New Haven, CT 06520., eric.pamer{at}yale.edu (E-mail), 203-785-3561 (phone), 203-785-3864 (fax)
Major histocompatibility complex (MHC) class Ib molecules have been implicated in CD8+ T cellmediated defenses against intracellular bacterial infection, but the relative importance of MHC class Ibrestricted T cells in antimicrobial immunity is unknown. In this report, we use MHC tetramers to characterize T cell responses restricted by H2-M3, an MHC class Ib molecule that selectively presents N-formyl peptides. We find that sizeable H2-M3restricted T cell responses, occurring earlier than MHC class Iarestricted T cell responses, are mounted after primary infection with the intracellular bacterium Listeria monocytogenes. These H2-M3restricted T cells are cytolytic and produce interferon
. However, after a second L. monocytogenes infection, H2-M3restricted memory T cell responses are minor in comparison to the much larger MHC class Iarestricted responses. This first direct characterization of an MHC class Ibrestricted T cell response indicates that CD8+ T cells responding to L. monocytogenes infection can be divided into two groups: H2-M3restricted responses, which provide rapid and quantitatively substantial effector function during primary infections but contribute relatively little to memory responses, and MHC class Iarestricted responses, which expand later during primary infection but form memory T cells that respond rapidly and dramatically in response to subsequent infections by the same pathogen.
Key Words: H2-M3, major histocompatibility complex class Ib molecules, cytotoxic T lymphocytes, Listeria monocytogenes, bacterial infection
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