Antigen and G-Protein Coupled Receptor signaling differentially control CD8 T cell motility immediately before and after virus clearance in a primary infection

Abstract

17 In mice, experimental influenza virus infection stimulates CD8 T cell infiltration of the airways.18 Virus is cleared by day 9, and between days 8 and 9 there is an abrupt change in CD8 T cell 19 motility behavior transitioning from low velocity and high confinement on day 8, to high velocity 20 with continued confinement on day 9. We hypothesized that it is loss of virus and/or antigen 21 signals in the context of high chemokine levels that drives the T cells into a rapid surveillance 22 mode. Virus infection induces chemokine production, which may change when the virus is 23 cleared. We therefore sought to examine this period of rapid changes to the T cell environment in 24 the tissue and seek evidence on the roles of peptide-MHC and chemokine receptor interactions.25 Experiments were performed to block G protein coupled receptor (GPCR) signaling with Pertussis 26 toxin (Ptx). Ptx treatment generally reduced cell velocities and mildly increased confinement, 27 except on day 8 when velocity increased and confinement was relieved, suggesting chemokine 28 mediated arrest. Blocking specific peptide-MHC with monoclonal antibody unexpectedly 29 decreased velocities on days 7 through 9, suggesting TCR/peptide-MHC interactions promote 30 cell mobility in the tissue. Together, these results suggest the T cells are engaged with antigen 31 bearing and chemokine producing cells that affect motility in ways that vary with the day after 32 infection. The increase in velocities on day 9 were reversed by addition of specific peptide, 33 consistent with the idea that antigen signals become limiting on day 9 compared to earlier time 34 points. Thus, antigen and chemokine signals act to alternately promote and restrict CD8 T cell 35 motility until the point of virus clearance, suggesting the switch in motility behavior on day 9 may 36 be due to a combination of limiting antigen in the presence of high chemokine signals as the virus 37 is cleared. 39 Introduction40 Influenza viruses infect roughly 12 percent of the population in any given year [1]. This leads to 41 lost productivity, hospitalizations, and deaths. In the 2017-18 season there was a record 80,000 3 42 deaths in the US alone [2]. In 2018-19, the northern hemisphere experienced the longest flu 43 season in over 20 years [3]. Understanding how the immune system controls influenza infection 44 is paramount to the development of improved vaccination strategies and for understanding the 45 disease process itself. Cytotoxic CD8 T cells are responsible for the initial clearance of infected 46 cells, especially in a primary infection when there are no pre-existing antibodies or other types of 47 adaptive immunity [4, 5]. In order to reach the site of infection, the trachea and airway epithelium, 48 the CD8 T cells must traffic through the circulation, exit into the tissue, and migrate within the 49 tissue before crossing into the epithelial surface. There are many things in the tissue 50 microenvironment that the T cells must interact and communicate with, and many feature...