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Infect. Immun. doi:10.1128/IAI.00563-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Enumeration of cytotoxic CD8 T cells ex vivo during the response to Listeria monocytogenes infection

David H. Smith Center for Vaccine Biology and Immunology, and the Department of Microbiology and Immunology, University of Rochester Medical Center, NY 14642

^* To whom correspondence should be addressed. Email: Tim_Mosmann{at}urmc.rochester.edu.

	Abstract

Cytotoxicity is a key effector function of CD8 T cells. However, what proportion of antigen-specific CD8 T cells in vivo exerts cytotoxic activity during a functional CD8 T-cell response to infection still remains unknown. We used the Lysispot assay to directly enumerate cytotoxic CD8 T cells from the spleen ex vivo during the immune response to infection with the intracellular bacterium Listeria monocytogenes. We demonstrate that not all antigen-responsive IFN-secreting T cells display cytotoxic activity. Most CD8 T cells detected at early time-points of the response were cytotoxic. This percentage continuously declined during both the expansion and contraction phases to about 50% at the peak and to <10% of IFN producing cells in the memory phase. As described for clonal expansion, this elaboration of a program of differentiation after an initial stimulus was not affected by antigen or CD4 help; but, like proliferation, could be influenced by later re-infection. These data indicate that cytotoxic effector function during the response to infection is regulated independently from IFN-secretion, expansion or contraction of the overall CD8 T cell response.