Investigating the impact of the ectromelia virulence factor C15 on early responses to infection in the draining lymph node 9307

Abstract Description Orthopoxviruses, such as variola and Mpox, encode a myriad of immunomodulatory proteins to promote pathogenesis. One notable family is the B22 family of proteins, which are conserved virulence factors that are generally described to inhibit T cell activation in vitro and ex vivo. However, we recently determined that the ectromelia virus (ECTV) B22 protein, C15, also facilitates early viral replication in C57BL/6 mice through the targeting of natural killer (NK) cell-mediated viral control. Current evidence suggests that C15 inhibits cell-cell contacts between NK cells and infected cells, but the immunological consequences and the underlying cellular mechanisms of this inhibition remain unknown. Here, we used flow cytometry as well as transcriptomic analysis to further dissect the immune response within the draining lymph node during WT or ECTVΔC15 infection. Using quantitative PCR, we found that C15 exerts a replicative advantage as early as 32 hours post-infection. Furthermore, in contrast to expected phenotypes, we found significantly more IFNγ+ NK cells 48 hours post-infection with WT ECTV. Bulk RNA sequencing has identified several candidate transcription factors that may underly these phenotypic differences, and future work seeks to use single-cell RNA sequencing to identify key changes within cell subsets. Overall, we conclude that C15 functions between 24 and 32 hours post-infection to modulate innate immune responses and transcriptional responses to infection. Funding Sources Supported by NIH/NIAID R01AI182049-02 and F31AI183694-01 Topic Categories Viral Immunology (VIR)