Antigen presentation by non-classical antigen-presenting cells has recently been shown to be relevant for priming CD4+ T-cell responses. Intestinal innate lymphoid cells (ILCs) and epithelial cells (IECs) have been shown to express class II major histocompatibility complex (MHCII) molecules and prime CD4+ T-cell responses toward pathobionts or pathogenic bacteria. More specifically, RORγt ILCs primed microbiota-induced iTreg cell differentiation, whereas it remains unclear how epithelial MHCII expression influences T-cell differentiation. MHCII expression by IECs was shown to be relevant for promoting epithelial cell remodeling and supporting intestinal stem cell renewal. Furthermore, the relevance of MHCII expression by intestinal stromal cells (ISCs) and its role in regulating T-cell responses remain unknown. MHCII expression in lymph node stromal cells was shown to dampen CD4+ T cell responses and induce tolerance.
Our preliminary data show that MHCII molecules (Ciita, Cd74, RelbH2-Eb1, H2-Aa, He-DMb1, H2-Ab1, Ceacam10, Sectm1a/1b, Cd320) are upregulated in both IECs and ISCs in intestinal inflammation. Single-cell sequencing of intestinal immune (CD45+), epithelial (EpCAM+, CD45–), and stromal cells isolated from colitic mice (H.h.+anti-IL10R model) showed upregulation of MHCII-related molecules in epithelial and stromal cells compared with steady-state mice. We now want to address the relevance of MHCII expression in IECs and ISCs on the induction and modulation of microbiota-specific CD4+ T-cell responses in steady-state and intestinal inflammation. We will use the Helicobacter hepaticus (Hh) colitis model and combine it with adoptive transfer approaches using Hh-specific TCR transgenic mice (HH7-2tg). We have imported the HH7-2tg mice and crossed them with Rag-deficient mice and the congenic marker CD90.1 to allow tracking of adoptively transferred cells. Furthermore, we have now imported MHCfl/fl mice (B6.129X1-H2-Ab1tm1Koni/J #Jax 013181) and initiated the breeding of MHCfl/fl mice with Villin-Cre/ERT2, Col1a2-Cre/ERT2, ACTB-Cre/ERT2, and Cad5-Cre/ERT2 mice to specifically delete MHCII from different non-immune cell types at different time points during the course of colitis.
Aim 1.1: Quantifying MHCII expression on epithelial and stromal cells and identifying signals that promote MHCII expression
Aim 1.2: Perturbation of MHCII to dissect the role of antigen presentation by epithelial and stromal cells in microbiota-specific CD4+ T-cell generation and differentiation.