Conditional silencing of H-2D^bclass I molecule expression on dendritic cells modulates the protective and pathogenic kinetics of virus-antigen specific CD8 T cell responses during Theiler’s Virus infection

Abstract

Theiler's murine encephalomyelitis virus (TMEV) infection of the central nervous systemis rapidly cleared in C57BL/6 mice by an anti-viral CD8 T cell response restricted by the MHC class I molecule, H-2D b . While the CD8 T cell response against neurotropic viruses is well characterized, the identity and function of the antigen presenting cell(s) involved in this process is(are) less well defined. To address this gap in knowledge, we developed a novel C57BL/6 H-2D b conditional knockout mouse that expresses an H-2D b transgene in which the transmembrane domain locus is flanked by LoxP sites. We crossed these H-2D b LoxP mice with MHC class I-deficient mice expressing Cre-recombinase under either the CD11c or LysM promoter in order to silence H-2D b restricted antigen presentation predominantly in dendritic cells or macrophages, respectively. Upon challenge with intracranial TMEV infection, we observe that CD11c+ APCs are critical for early priming of CD8 T cells against the immunodominant TMEV peptide VP2 121-130 presented in the context of the H-2D b molecule. This stands in stark contrast to later time points post TMEV infection where CD11c+ APCs appear dispensable for the activation of antigen-specific T cells; the functionality of these late-arising antiviral CD8 T cells is reflected in the restoration of viral control at later time points. These latearising CD8 T cells also retain their capacity to induce blood-brain barrier disruption. In contrast, when H-2D b restricted antigen presentation was selectively silenced in LysM+ APCs there was no overt impact on the priming of D b :VP2 121-130 epitope-specific CD8 T cells, although a modest reduction in immune cell entry into the CNS was observed. This work establishes a model system which enables critical dissection of MHC class I restricted antigen presentation to T cells, revealing cell specific and temporal features involved in the generation of antiviral CD8 T cell responses. Employing this novel system, we established CD11c+ cells as a pivotal driver of acute, but not later-arising, antiviral CD8 T cell responses against the TMEV immunodominant epitope VP2 121-130 , with functional implications both for T cell-mediated viral control and immunopathology. Class I conditional knockout mice were developed through construction of an H-2D b transgene, in which the transmembrane (TM) domain is flanked by LoxP sites. This transgene was introduced into C57BL/6 mice deficient in H-2D b and H-2K b , leaving the floxed D b as the onlyMHC class I molecule expressed by nucleated cells (Fig 1A) [33]. Crossing this transgenic mouse line with mice expressing Cre-recombinase under the CD11c, LysM, or CMV promoter, also on total MHC class I knockout backgrounds, allowed for CD11c+ cell specific, LysM+ cell specific, or ubiquitous ablation of MHC-I expression, respectively ( Fig 1B, Fig 1C, Fig 1D).Resultant mice will be referred to as CD11c D b conditional knockout (cKO), LysM D b cKO, CMV D b cKO, or Cre-littermates depending on whether the F1 generation pups inherited the...