XBP1 and Autoimmunity: In mature T cells, XBP1 regulates subset differentiation through distinct mechanisms: (1) XBP1S drives Th2 responses via enhanced proliferation and cytokine production [33,46], (2) stress-induced XBP1 promotes Th17 differentiation in autoimmunity [47], and (3) XBP1S enhances CD8+ effector function through upregulation of killer cell lectin-like receptor G1 [48].