A 20-year-old woman presents with a 4-week history of dry mouth, fatigue, fever, and yellow sclerae. Physical examination shows mild jaundice and hepatomegaly Serum total bilirubin is 3.3 mg/dL. Serologic markers for viral hepatitis are negative. The anti-mitochondrial antibody test is negative. A liver biopsy discloses parenchymal and periportal inflammatory cell infiltrates composed primarily of lymphocytes and plasma cells. The patient's signs and symptoms abate following 2 months of treatment with steroids. Which of the following is the most likely diagnosis?