Exploring Antiviral Activities of Barrier Tissue-Resident Lymphocytes

Abstract

Barrier tissues such as the oral mucosa and skin are continuously exposed to a barrage of pathogens. To protect from this constant influx of pathogens, barrier tissue-resident lymphocytes are strategically placed within these tissues to sense and limit initial viral infection or spread. Barrier tissue-resident lymphocytes are comprised of various lymphoid cell types spanning both innate and adaptive immunity which vary in aspects of both spatial and temporal control. The exact mechanisms and processes through which these barrier tissue-resident cells respond to viral infection and are distributed in relation to each other within their tissue microenvironments are incompletely understood. Herein, tissue resident lymphoid cells, including NK cells and innate lymphoid I cells (ILC1s) (which together comprise group I ILCs), dendritic epidermal T cells (DETCs), and tissue-resident memory T cells (TRM) are studied to understand their unique responses to local viral infection with the prototypical poxvirus, vaccina virus (VACV). Using multiple microscopy approaches, flow cytometry, and single-cell RNA sequencing this dissertation shows that T cells and group I ILCs are interspersed in the oral mucosa but remain separated from each other in the skin throughout the course of infection; keeping this spatial conformation as the T cells become TRM. Further, a lower number of TRM establish in the oral mucosa compared to the skin but find that TRM do not vary transcriptionally across tissue. As such, TRM limit viral replication at similar levels in both tissues despite differences in number. Sequencing data also reveals higher transcripts encoding for cytotoxic molecules in group I ILCs when compared to TRM in the oral mucosa. One of these cytotoxic molecules, granzyme C, was expressed by ILC1s, DETCs and TRM in surface epithelia of the oral mucosa and skin. Upon further investigation, granzyme C is dynamic and is upregulated during viral induced inflammation and occurs independent of cognate antigen. Interestingly, exogenous administration of the cytokine IL-15, a lymphocyte proliferation factor, induces upregulation of granzyme C in skin-resident T cells. Together, this dissertation demonstrates how barrier-tissue resident lymphocytes have unique interactions across the barrier tissues examined and express similar effector molecules. As barrier tissues serve as the first line of defense against viral infection, understanding how barrier tissue-resident lymphocytes limit viral infection and how they are distributed may allow for the development of therapeutics to enhance their antiviral properties and prevent severe viral disease.