ABSTRACT
Immune suppression by Treg has been demonstrated in a number of models, but the mechanisms of this suppression are only partly understood. Recent work has suggested that Tregs may suppress by directly killing immune cell populations in vivo in a perforin- and granzyme B-dependent manner. To establish whether perforin is necessary for the regulation of immune responses in vivo, we examined OVA-specific CD8(+) T cell responses in WT and PKO mice immunized with OVA and α-GalCer and the expansion of WT OT-I CD8(+) T cells adoptively transferred into WT or PKO mice immunized with DC-OVA. We observed similar expansion, phenotype, and effector function of CD8(+) T cells in WT and PKO mice, suggesting that CD8(+) T cells were subjected to a similar amount of regulation in the two mouse strains. In addition, when WT and PKO mice were depleted of Tregs by anti-CD25 mAb treatment before DC-OVA immunization, CD8(+) T cell proliferation, cytotoxicity, and cytokine production were increased similarly, suggesting a comparable involvement of CD25(+) Tregs in controlling T cell proliferation and effector function in these two mouse strains. These data suggest that perforin expression is not required for normal immune regulation in these models of in vivo CD8(+) T cell responses induced by immunization with OVA and α-GalCer or DC-OVA.
Subject(s)
CD4-Positive T-Lymphocytes/cytology , CD8-Positive T-Lymphocytes/immunology , Interleukin-2 Receptor alpha Subunit/metabolism , Lymphocyte Depletion , Pore Forming Cytotoxic Proteins/deficiency , Animals , CD4-Positive T-Lymphocytes/immunology , CD8-Positive T-Lymphocytes/cytology , Cell Differentiation , Cell Proliferation , Cell Survival , Dendritic Cells/metabolism , Galactosylceramides/metabolism , Immunization , Lectins, C-Type , Mice , Mice, Inbred C57BL , Mice, Knockout , Ovalbumin/immunology , Pore Forming Cytotoxic Proteins/metabolism , Receptors, Immunologic/metabolism , T-Lymphocytes, RegulatoryABSTRACT
Tumor-infiltrating dendritic cells are often ineffective at presenting tumor-derived antigen in vivo, a defect usually ascribed to the suppressive tumor environment. We investigated the effects of depleting CD4(+)CD25(+) "natural" regulatory T cells (Treg) on the frequency, phenotype and function of total dendritic cell populations in B16.OVA tumors and in tumor-draining lymph nodes. Intraperitoneal injection of the anti-CD25 monoclonal antibody PC61 reduced Treg frequency in blood and tumors, but did not affect the frequency of tumor-infiltrating dendritic cells, or their expression of CD40, CD86 and MHCII. Tumor-infiltrating dendritic cells from PC61-treated or untreated mice induced the proliferation of allogeneic T cells in vitro, but could not induce proliferation of OVA-specific OTI and OTII T cells unless specific peptide antigen was added in culture. Some proliferation of naïve, OVA-specific OTI T cells, but not OTII T cells, was observed in the tumor-draining LN of mice carrying B16.OVA tumors, however, this was not improved by PC61 treatment. Experiments using RAG1(-/-) hosts adoptively transferred with OTI and CD25-depleted OTII cells also failed to show improved OTI and OTII T cell proliferation in vivo compared to C57BL/6 hosts. We conclude that the defective presentation of B16.OVA tumor antigen by tumor-infiltrating dendritic cells and in the tumor-draining lymph node is not due to the presence of "natural" CD4(+)CD25(+) Treg.
