Tubulointerstitial nephritis (TIN) is a kind of tubular disorder and surely an immune-mediated disease. The histological features include immune cell infiltration and tubulitis, but relatively spares the glomeruli and vessels. Most of acute TIN (ATIN) are attributable to drugs and toxins, and the current therapeutic approach is the corticosteroid use. Nevertheless, the recovery rate from this does not exceed 50%. Accordingly, we need more solid evidence to use corticosteroids based on novel biomarkers. Recent immunological understanding and experience with further cases (e.g., immune checkpoint inhibitor-induced ATIN) will enhance our success in diagnosis and treatment of TIN.