Understanding the role of dendritic cell subsets in the generation of a CD8+ T cell response following pulmonary vaccinia viral infection

Unlike many other tissues, the lung is constantly assaulted with foreign antigens, both environmental and infectious. This includes a large number of viruses which spread via aerosolized droplets. In order for the body to mount an adaptive immune response to a pathogen, T cells circulating through lymph nodes (LN) must be alerted to the presence of infection in the periphery. This occurs as a result of presentation of pathogen derived epitopes on professional antigen presenting cells (APC), primarily dendritic cells (DC). While an important role for dendritic cells (DC) as the activators of naive T cells is clear, the contribution of distinct DC subsets in this process is less understood. Multiple DC subsets are present within the lung tissue (CD103 + DC and CD11b+ DC) and draining lymph nodes (MLN) (CD8&agr;+), and as such, all are potential regulators of T cell activation (for review see1,2). These studies sought to understand how DC subsets contribute to the generation of virus-specific CD8+ T cells following pulmonary viral infection.;We have developed a model of pulmonary vaccinia (VV) infection in order to address the role of DC subsets in activating naïve CD8+ T cells. The use of a recombinant virus expressing eGFP allowed us to identify DC that had access to viral antigen. Following intratracheal instillation of the cell permeable dye cell tracker orange (CTO) we were able to delineate DC in the MLN that had trafficked from the lung. These methods, along with cell sorting, have allowed us to determine which DC subsets were capable of priming naïve CD8+ T cells ex vivo. While CD103+ DC and CD11b+ DC in the lung showed similar expression of eGFP, the eGFP+CD11b+ DC failed to migrate to the MLN. The eGFP− CD11b + DC that did migrate were poor inducers of CD8+ T cell activation, as were LN resident CD8&agr;+ DC. Our data identified CD103+ DC as the most potent activators of naïve CD8+ T cells in response to pulmonary VV infection.;During the course of these studies, we identified CD8&agr;+CD103 + DC subset present in the MLN, but absent in the lung. While this DC subset has been noted in the past, this is the first set of studies to extensively characterize this population. We found that these CD8&agr; +CD103+ DC resemble the CD8&agr;−CD103 + DC in expression of surface markers CD205 and CD24. CTO labeling studies suggested CD8&agr;+CD103+ DC migrate to the MLN from the lung, although with delayed migration kinetics compared to CD8&agr;−CD103+ DC. Finally, we noted that while the CD8&agr;+CD103+ DC have enhanced expression of co-stimulatory molecules in response to toll-like receptor (TLR) stimulation, incubation with naïve CD8+ T cells resulted in less T cell division than was seen with CD8&agr;−CD103 + DC. While the role of the CD8&agr;+CD103 + DC in CD8+ T cells activation has yet to be fully elucidated, it appears that these DC are a population with distinct properties, separate from airway CD8&agr;-+CD103+ DC and LN resident CD8&agr;+CD103− DC.