Fine regulation of the Rasimitogen-activating protein kinase (MAPK) pathway is crucial in controlling the survival, proliferation, and development of various types of cells. Ras-activating protein-like 3 (Rasal3) is a T cell-specific Ras GTPase-activating protein that negatively regulates T cell receptor (TCR)-induced activation of Ras/MAPK pathway. Rasal3-deficient mice showed a decreased number of naive T cells because Rasal3 is required for the survival of naive T cells. In the current study, we observed ameliorated Typel T helper (Th1) cell- and Type2 T helper (Th2) cell-dependent contact hypersensitivity reactions in Rasal3-deficient mice, along with a marked shortage of T cells at regional lymph node. Activated Rasa13-deficient T cells showed an increased cell death with reduced Bc12 expression, suggesting that Rasal3 is required for the survival of not only naive T cells but also activated T cells. Collectively, Rasal3 controls the magnitude of inflammatory responses through the survival of both naive T cells and activated T cells in vivo. (C) 2017 Elsevier Inc. All rights reserved.