A patient with a suspected autoimmune disorder exhibits antibodies directed against self-antigens, leading to tissue damage and inflammation. Which of the following mechanisms is primarily responsible for the development of autoimmune diseases?

Correct Answer: A

Rationale: The correct answer is A: Loss of self-tolerance. This is because autoimmune diseases result from a breakdown in the immune system's ability to distinguish between self and non-self antigens, leading to the production of antibodies against self-antigens. When self-tolerance is lost, immune cells mistakenly target the body's own tissues, causing tissue damage and inflammation. Choice B (Failure of innate immunity) is incorrect because autoimmune diseases are primarily driven by adaptive immunity rather than innate immunity. Choice C (Defective T cell activation) is incorrect as T cells play a critical role in the immune response to self-antigens in autoimmune diseases. Choice D (Impaired phagocytosis) is incorrect as phagocytosis is a mechanism primarily involved in the removal of pathogens, not in the development of autoimmune diseases.

Correct Answer: D

Rationale: The correct answer is D: Bronchodilator therapy. Bronchodilators help to relax and open up the airways, which can improve airflow and reduce symptoms such as cough, sputum production, and dyspnea in patients with chronic bronchitis. This intervention can help manage the patient's symptoms and improve their quality of life by making it easier for them to breathe. A: Smoking cessation counseling is important for overall management of chronic bronchitis, but it does not directly address the patient's current symptoms. B: Oral antibiotic therapy may be indicated if there is evidence of a bacterial infection, but it is not the first-line treatment for managing chronic bronchitis symptoms. C: Home oxygen therapy may be necessary for patients with severe hypoxemia, but it is not typically the first intervention for managing symptoms of chronic bronchitis without evidence of significant oxygen desaturation.

Correct Answer: A

Rationale: The correct answer is A: Ceftriaxone and azithromycin. Ceftriaxone covers Streptococcus pneumoniae, the most common pathogen in CAP, while azithromycin covers atypical pathogens like Mycoplasma pneumoniae. Vancomycin and piperacillin/tazobactam (choice B) are not first-line treatments for CAP. Ampicillin-sulbactam and levofloxacin (choice C) cover some pathogens but not as comprehensively as ceftriaxone and azithromycin. Clindamycin and cefepime (choice D) do not provide adequate coverage for typical CAP pathogens.

Correct Answer: C

Rationale: Rationale: - ARDS is characterized by severe hypoxemia and respiratory distress. - Tachypnea is a hallmark sign of ARDS due to the body's compensatory mechanism to increase oxygenation. - Hypoxemia refractory to supplemental oxygen signifies the inability to improve oxygen levels despite intervention. - Choices A, B, and D do not align with typical manifestations of ARDS, as they do not directly reflect severe hypoxemia or respiratory distress.

Correct Answer: C

Rationale: The correct answer is C: Acquired von Willebrand syndrome. This condition is characterized by a defect in von Willebrand factor function, leading to prolonged bleeding time and mucocutaneous bleeding. Normal platelet count rules out Glanzmann thrombasthenia and Bernard-Soulier syndrome which are platelet disorders. Normal PT and aPTT rule out Hemophilia A, a coagulation factor deficiency. Acquired von Willebrand syndrome is the most likely cause based on the clinical presentation and laboratory findings.