PROJECT SUMMARY/ABSTRACT Auto-reactive CD4+ T cells play an important role in the development of autoimmune diseases such as systemic lupus erythematosus (SLE) and are often entangled in a stimulatory loop with other immune cells. Autoantibodies that cause tissue damage and release of self-antigens lead to further spurious activation and differentiation of self-reactive CD4+ T cells. It is not known through what molecular mechanisms aberrant self-recognition can cause loss of intrinsic control in T cells. Patrolling T cells constantly encounter self-peptides (self-p/MHC) and self-recognition drives low-level, tonic signals. Since the late 1980's, tonic signals have been detected in resting T cells but the function of such signals have long remained a mystery. During 1R01AI104789 we uncovered that tonic signals dynamically control the naïve CD4+ T cell state. Tonic signals suppress spurious activation and differentiation of naïve T cells through the transcriptional induction of target genes that function as brakes. On the other hand, we also revealed that tonic signals prime the cellular activity of naïve T cells by translating other target genes that elevate the energetic and metabolic state. This second type of tonic signal is transmitted through a newly discovered tonic Rasgrp1-mTORC1 pathway and results in constitutive mRNA translation of roughly 3000 genes in resting CD4+ T cell. Tonic mTORC1 signals are surprisingly selective and robust and are aberrantly elevated by self-recognition and by a SNV (Single nucleotide variant) in Rasgrp1. T cells with a Rasgrp1Anaef variant display increased tonic-mTORC1 signals that aberrantly translate mRNA targets, spontaneously differentiate in ICOS+PD-1+CXCR5-Bcl6- T peripheral helper (TPH) cells, and cause pathogenic production of autoantibodies by B cells. These studies provide a framework to obtain molecular or mechanistic understanding of self-recognition, tonic signaling, T cell biology, and autoimmunity. Our renewal focuses on understanding how aberrant self-recognition and increased tonic Rasgrp1- mTORC1 signals can lead to altered metabolism in naïve CD4+ T cells over time and ultimately drive spurious activation and differentiation of pathogenic CD4+ T cell subsets. We will investigate the new non- canonical, tonic Rasgrp1-mTORC1 signaling pathway that we discovered (Aim 1). We will establish the in vivo role of tonic Rasgrp1-mTORC1 in T cells as well as the metabolic and immunological implications of this signal and self-recognition for naïve T cells (Aim 2). Lastly, we will characterize the tonic signals and metabolic state of self-reactive CD4+ T cells from SLE and RA patient samples with single cell resolution (Aim 3). The synergistic aims and secured new cell lines, new mouse models, new patient sample pipelines, and innovative, single cell-resolution technology platforms will allow us to make significant contributions towards increased mechanistic understanding of self-recognition, tonic s...