A 45-year-old woman with a history of systemic lupus erythematosus (SLE) on hydroxychloroquine and prednisolone presents with a 3-week history of progressive dyspnea, cough, and fever. Chest X-ray shows bilateral interstitial infiltrates. High-resolution CT (HRCT) chest reveals ground-glass opacities and areas of consolidation. Bronchoalveolar lavage (BAL) fluid shows a lymphocytic infiltrate with elevated LDH (450 U/L) and CD4/CD8 ratio of 0.8. Transbronchial lung biopsy reveals mononuclear cell infiltration with apoptotic bodies in the alveolar septa, consistent with lupus pneumonitis. Serum anti-dsDNA antibodies are markedly elevated. What is the most appropriate next step in management?