Which of the following mechanisms is responsible for the phenomenon of immunological memory, wherein the immune system mounts a faster and more robust response upon re-exposure to a previously encountered pathogen?

Correct Answer: A

Rationale: Immunological memory is primarily maintained by the clonal expansion of memory B cells. Memory B cells are a type of long-lived immune cell that originates from previously activated B cells during an immune response to a pathogen. When the immune system encounters the same pathogen again, memory B cells can quickly recognize and respond to it by undergoing rapid clonal expansion and differentiation into plasma cells that produce specific antibodies. This quick and robust response leads to the more efficient elimination of the pathogen during secondary exposure, resulting in the faster and stronger immune response characteristic of immunological memory.

Correct Answer: A

Rationale: Opsonization refers to the process by which antibodies bind to the surface of pathogens, marking them for destruction by phagocytes or complement proteins. This coating of antibodies enhances the ability of the immune system to recognize and eliminate the pathogens effectively. Phagocytes (such as macrophages and neutrophils) are better able to engulf and digest pathogens that have been opsonized, as the antibodies attached to the pathogen surface signal to the phagocytes that they are foreign invaders. This process is crucial in the body's immune response to infections and helps in clearing pathogens from the system.

Correct Answer: C

Rationale: In a patient with ARDS who is experiencing refractory hypoxemia despite maximal ventilatory support and prone positioning, the use of extracorporeal membrane oxygenation (ECMO) is a potentially life-saving adjunctive therapy. ECMO works by providing temporary support for gas exchange outside the body, allowing the lungs to rest and heal while providing adequate oxygenation and carbon dioxide removal. The use of ECMO has been associated with improved oxygenation and reduced mortality in severe cases of ARDS, especially in patients who fail conventional therapies. High-frequency oscillatory ventilation (HFOV) has not consistently shown mortality benefit in ARDS, continuous renal replacement therapy (CRRT) is not directly indicated for hypoxemia in ARDS, and inhaled nitric oxide (iNO) has shown limited benefit in improving oxygenation in ARDS without a clear impact on mortality.

Correct Answer: A

Rationale: Acute respiratory distress syndrome (ARDS) is a serious and life-threatening condition characterized by rapid onset of respiratory failure, severe hypoxemia (low oxygen levels in the blood), and non-cardiogenic pulmonary edema. The hallmark of ARDS is severe hypoxemia that is difficult to correct even with high levels of supplemental oxygen. Patients with ARDS often require mechanical ventilation to maintain adequate oxygen levels. Severe cough with purulent sputum production, chest pain exacerbated by deep breathing, and productive cough with hemoptysis are not typical features of ARDS.

Correct Answer: B

Rationale: Disseminated intravascular coagulation (DIC) is a condition characterized by widespread activation of coagulation leading to both thrombosis and hemorrhage. In patients with chronic liver disease, especially in the setting of advanced cirrhosis, DIC can develop due to factors such as decreased synthesis of coagulation factors and impaired clearance of activated clotting factors. The patient in this scenario presents with signs of both abnormal bleeding (bruising, petechiae, mucosal bleeding) and laboratory findings consistent with DIC, including prolonged prothrombin time (PT) and activated partial thromboplastin time (aPTT) along with decreased platelet count.