title: Direct in vivo evidence of CD4+ T cell requirement for CTL response and memory via pMHC-I targeting and CD40L signaling.
abstract: CD4(+) T cell help contributes critically to DC-induced CD8(+) CTL immunity. However, precisely how these three cell populations interact and how CD4(+) T cell signals are delivered to CD8(+) T cells in vivo have been unclear. In this study, we developed a novel, two-step approach, wherein CD4(+) T cells and antigen-presenting DCs productively engaged one another in vivo in the absence of cognate CD8(+) T cells, after which, we selectively depleted the previously engaged CD4(+) T cells or DCs before allowing interactions of either population alone with naïve CD8(+) T cells. This protocol thus allows us to clearly document the importance of CD4(+) T-licensed DCs and DC-primed CD4(+) T cells in CTL immunity. Here, we provide direct in vivo evidence that primed CD4(+) T cells or licensed DCs can stimulate CTL response and memory, independent of DC-CD4(+) T cell clusters. Our results suggest that primed CD4(+) T cells with acquired pMHC-I from DCs represent crucial "immune intermediates" for rapid induction of CTL responses and for functional memory via CD40L signaling. Importantly, intravital, two-photon microscopy elegantly provide unequivocal in vivo evidence for direct CD4-CD8(+) T cell interactions via pMHC-I engagement. This study corroborates the coexistence of direct and indirect mechanisms of T cell help for a CTL response in noninflammatory situations. These data suggest a new "dynamic model of three-cell interactions" for CTL immunity derived from stimulation by dissociated, licensed DCs, primed CD4(+) T cells, and DC-CD4(+) T cell clusters and may have significant implications for autoimmunity and vaccine design.
authors.affiliation: Research Unit, Saskatchewan Cancer Agency, Department of Oncology, University of Saskatchewan, Saskatoon, Saskatchewan Canada.
authors.forename: Khawaja Ashfaque
authors.initials: KA
authors.lastname: Ahmed
authors.forename: Lu
authors.initials: L
authors.lastname: Wang
authors.forename: Manjunatha Ankathatti
authors.initials: MA
authors.lastname: Munegowda
authors.forename: Sean J
authors.initials: SJ
authors.lastname: Mulligan
authors.forename: Sean
authors.initials: S
authors.lastname: Mulligan
authors.forename: John R
authors.initials: JR
authors.lastname: Gordon
authors.forename: Philip
authors.initials: P
authors.lastname: Griebel
authors.forename: Jim
authors.initials: J
authors.lastname: Xiang
mesh_terms: D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D023201:CD40 Ligand / Q000502:physiology*; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D045744:Cell Line, Tumor; D003602:Cytotoxicity, Immunologic; D005260:Female; D018390:Gene Targeting / Q000379:methods; D015395:Histocompatibility Antigens Class I / Q000276:immunology / Q000378:metabolism* / Q000502:physiology*; D007156:Immunologic Memory; D008213:Lymphocyte Activation / Q000276:immunology; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D015398:Signal Transduction / Q000276:immunology*
chemical_list: D015395:Histocompatibility Antigens Class I; D023201:CD40 Ligand