Role of Type I Interferon Signaling in Regulating Intestinal γδ IEL Homeostasis and Effector Function
Authors: Jia Luo , Edelblum Karen L 
Published: June 2021

Intraepithelial lymphocytes expressing the γδ T cell receptor (γδ IELs) function as a first line of defense against injury or microbial invasion. The majority of the γδ IELs express the Vγ7 T cell receptor (TCR); however, the epithelial compartment also contains Vγ1+ or Vγ4+ cells, which are typically found in peripheral lymphoid organs. Type I interferon (IFN) is a critical immunomodulatory cytokine that contributes to the innate immune response and the maintenance of mucosal homeostasis. Ubiquitously expressed, type I IFNs activate the IFNα/β receptor (IFNAR) and initiate downstream signaling through signal transducer and activator of transcription 1 (STAT1). In response to type I IFN, STAT1 has been shown to inhibit conventional CD8 T cell proliferation. Tonic type I IFN signaling has been shown to shape the intestinal lamina propria immune compartment, yet the role of type I IFN in regulating γδ IEL remains unknown. Thus, we hypothesize that type I IFN modulates γδ IEL proliferation and effector function. Morphometric analysis of γδ T cells in the jejunum of GFP γδ T cell reporter mice (TcrdEGFP, WT) and TcrdEGFP IFNAR‐deficient mice showed a 2.3‐fold increase in the number of γδ T cells in IFNAR KO mice compared to WT (p=0.004). We next investigated the composition of Vγ subsets in the epithelial compartment of IFNAR KO mice. Using flow cytometry, we found a substantial increase in Vγ7− IELs including a 3.4‐fold and 7.6‐fold increase in Vγ1+ and Vγ4+ IEL subsets, respectively. In contrast, Vγ7+ IELs were only increased by 1.8‐fold. To determine if the increased cell number was due to enhanced proliferation, mice were injected with 5‐ethynyl‐2’‐deoxyuridine (EdU). Indeed, all IFNAR KO γδ IEL subsets proliferated more compared to WT; however, proliferation was markedly increased in Vγ7− relative to Vγ7+ IELs (110% vs 30%). Consistent with its anti‐proliferative role, we found that total STAT1 expression was decreased by 45% in IFNAR KO γδ IELs compared to WT (p=0.02). To identify molecular pathways contributing to this phenotype, we performed RNA sequencing on sorted Vγ1+ and Vγ7+ IELs from WT and IFNAR KO mice. Genes associated with cell cycle and PI3K/Akt signaling were significantly increased in IFNAR KO γδ IEL subsets, as was IL‐4, which can activate PI3K signaling and promote CD8 T cell proliferation. Enhanced Il4 expression in IFNAR KO γδ IELs was validated by real‐time PCR. Since IL‐4 activation leads to STAT6 phosphorylation, we next assessed pSTAT6 in ex vivo cultured WT and IFNAR KO γδ IELs by flow cytometry. Basal pSTAT6 was elevated in IFNAR KO γδ IELs compared to WT, and the addition of anti‐IL‐4 antibody to IFNAR KO γδ IELs was sufficient to abrogate this response. Taken together, our findings demonstrate that tonic low level IFNAR signaling maintains γδ IEL homeostasis and regulates their effector function at steady‐state. Loss of IFNAR signaling promotes an expanded Vγ7− IEL compartment, which may result from reduced STAT1 and/or increased IL‐4 signaling.Support or Funding InformationRutgers University Busch Biomedical Research GrantThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.