A 35-year-old woman presents to the clinic with fatigue, shortness of breath, and jaundice. Physical examination reveals pallor and mild splenomegaly. Laboratory studies show anemia with an elevated reticulocyte count, indirect hyperbilirubinemia, and positive serum lactate dehydrogenase (LDH). A Direct Coombs test is positive. Which of the following is the most likely diagnosis?

A 45-year-old man undergoes a kidney transplant for end-stage renal disease. Ten days post-transplant, he develops fever, hypertension, and reduced urine output. Laboratory tests show elevated serum creatinine. A renal biopsy reveals dense lymphocytic infiltration and tubulitis. What is the primary mechanism responsible for this patient’s acute transplant rejection?

A 32-year-old black woman presents with fatigue, dry cough, and chest pain for 3 months. She reports mild weight loss and intermittent low-grade fever. A chest X-ray reveals bilateral hilar lymphadenopathy. Laboratory testing shows elevated serum calcium and increased angiotensin-converting enzyme (ACE) levels. A biopsy of a lymph node shows noncaseating granulomas. What is the underlying mechanism responsible for her condition?

A 15-year-old male presents with intensely pruritic, erythematous papules and vesicles on his hands, especially between the fingers, shortly after working on a new project involving wood and varnish. He has no previous history of skin issues but mentions using a new type of wood treatment. What is the most likely mechanism of this reaction?

A 45-year-old male prison guard receives a PPD test as part of an annual health screening. He has no symptoms of active tuberculosis and no significant medical history. Forty-eight hours after PPD placement on the inner forearm, he returns for interpretation, and the site reveals a 15 mm area of induration with surrounding erythema. Which type of hypersensitivity reaction is responsible for this reaction?

A 47-year-old male presents with fever, weight loss, muscle weakness, and severe abdominal pain. Physical examination reveals livedo reticularis (a purplish, net-like skin discoloration) on his lower extremities and multiple tender nodules. Laboratory tests reveal elevated erythrocyte sedimentation rate (ESR), elevated C-reactive protein (CRP), and significant proteinuria. A biopsy of the skin lesion shows necrotizing inflammation of medium-sized arteries with fibrinoid necrosis. Which of the following reaction mechanisms is primarily associated with this patient’s condition?

A 50-year-old woman presents with a 6-month history of joint pain, stiffness, and swelling affecting both hands and wrists. She describes morning stiffness lasting more than an hour, which improves with activity. She also reports fatigue and occasional low-grade fevers. Physical examination reveals bilateral swelling and tenderness of the MCP and PIP joints. Laboratory tests show elevated rheumatoid factor (RF) and anti-citrullinated peptide antibodies (anti-CCP). X-ray of the hands shows joint space narrowing, periarticular osteopenia, and marginal erosions. Which of the following best describes the underlying mechanism of her condition?

A 35-year-old woman is rushed to the emergency department after a major car accident. She has sustained multiple fractures and internal injuries, with significant blood loss. Her initial hemoglobin is 6.2 g/dL, and a massive transfusion protocol is initiated using O-negative blood. Shortly after the transfusion, she develops fever, chills, hematuria, hypotension, and respiratory distress. Blood typing later reveals she has the Oh (Bombay) phenotype. What is the cause of this adverse reaction?

A 28-year-old woman presents to the clinic with complaints of double vision and difficulty swallowing, which worsen throughout the day. Neurological examination reveals bilateral ptosis and decreased muscle strength that improves after resting. A Tensilon test is performed and is positive. What type of hypersensitivity reaction is responsible for this patient’s condition?

A 65-year-old man with a history of smoking presents with hemoptysis, shortness of breath, and decreased urine output. His chest X-ray reveals bilateral alveolar infiltrates, and his urinalysis shows hematuria and red blood cell casts. Serum creatinine is elevated, and anti-GBM antibodies are positive. What is the most appropriate initial treatment?