Th1 cells mediate cellular immunity; IL-4 promotes IL-12 secretion by APC cells in dry-eye patients, which induces Th1 cells to secrete IFN-γ and tumor necrosis factor-alpha (TNF-α) that enhance the endoplasmic reticulum stress, reduce Ca2+ concentration, and stimulate cholinergic agonist secretion to reduce mucin secretion by goblet cells. The gene discussed is MUC5AC; the disease is Keratoconjunctivitis sicca.