A 26-year-old female presents with pain in the wrist and ankle joints for 6 months and a facial rash upon exposure to sunlight since summer. Exam: alopecia, irregular, circular skin lesions on the face and neck with slightly raised edges, multiple superficial ulcers in the oral cavity, liver palpable 0.5 cm below the costal margin, spleen just palpable below the costal margin. Laboratory tests: positive LE cells. Based on the revised American Rheumatology criteria, this meets the diagnosis of SLE. What is the first-line treatment for this case?