A patient with a chronic viral infection demonstrates persistently elevated levels of CD8+ cytotoxic T cells in their blood. Which of the following mechanisms is most likely responsible for this observation?

Correct Answer: B

Rationale: T cell exhaustion is a state of T cell dysfunction that arises during chronic viral infections or cancer. In the case of a chronic viral infection, the persistent exposure to viral antigens leads to continuous stimulation of CD8+ cytotoxic T cells. Over time, this sustained stimulation can lead to T cell exhaustion, characterized by the upregulation of inhibitory receptors, impaired effector functions, and reduced proliferative capacity. As a result, despite the elevated levels of CD8+ T cells in the blood, their function may be compromised, ultimately impacting the immune response against the viral infection. In contrast, activation-induced cell death (AICD) may contribute to T cell loss during chronic infections but would not explain the persistently elevated CD8+ T cell levels. Thymic involution refers to the age-related decline in thymus function, which is not directly related to the observed increase in CD8+ T cells. Antigenic

Correct Answer: D

Rationale: Spiral CT angiography is the most appropriate test for confirming the diagnosis of pulmonary embolism (PE) in a patient with suspected PE. It is a non-invasive imaging modality that can detect filling defects within the pulmonary vasculature indicative of a clot. This diagnostic test has high sensitivity and specificity for diagnosing PE, making it a valuable tool in the management of patients with suspected PE.

Correct Answer: D

Rationale: In a patient with acute exacerbation of COPD who presents with hypercapnia and respiratory acidosis, the most appropriate ventilatory strategy is invasive mechanical ventilation with a lung protective strategy. This involves using lower tidal volumes and limiting plateau pressures to prevent ventilator-induced lung injury.

Correct Answer: D

Rationale: Acute respiratory distress syndrome (ARDS) is a severe condition characterized by widespread inflammation in the lungs leading to increased pulmonary vascular permeability, non-cardiogenic pulmonary edema, and respiratory failure. In ARDS, the alveolar-capillary barrier is disrupted, resulting in fluid accumulation in the alveoli and impaired gas exchange.

Correct Answer: A

Rationale: Thrombotic thrombocytopenic purpura (TTP) is a rare but serious condition characterized by microangiopathic hemolytic anemia, thrombocytopenia, neurological abnormalities, fever, and renal dysfunction. The classic pentad of symptoms includes fever, neurologic changes, renal impairment, thrombocytopenia, and microangiopathic hemolytic anemia. The presence of petechiae, purpura, and mucosal bleeding along with thrombocytopenia, elevated serum creatinine, and schistocytes on peripheral blood smear are consistent with TTP. In TTP, there is usually a deficiency of ADAMTS13 (a von Willebrand factor-cleaving protease) leading to excessive platelet adhesion, aggregation, and microthrombi formation within small blood vessels. Treatment typically