A 68-year-old man comes to the emergency department with a 2-day history of fever, chills, and productive cough. His temperature is 38.9 C (102 F), blood pressure is 108/52 mm Hg, pulse is 102/min, and respirations are 26/min. Crackles and bronchial breath sounds are heard over the right lower lung. There is dullness to percussion over the same area. Chest x-ray reveals right lower lobe consolidation and a right-sided pleural effusion. The patient is started on the appropriate treatment, and a diagnostic thoracentesis is performed that shows an uncomplicated parapneumonic effusion. When a sterile sample of the inflammatory exudate is experimentally introduced into normal human tissue, rapid neutrophil locomotion is observed. Which of the following components of the exudate is most likely responsible for this observed effect?

Question

A 68-year-old man comes to the emergency department with a 2-day history of fever, chills, and productive cough.  His temperature is 38.9 C (102 F), blood pressure is 108/52 mm Hg, pulse is 102/min, and respirations are 26/min.  Crackles and bronchial breath sounds are heard over the right lower lung.  There is dullness to percussion over the same area.  Chest x-ray reveals right lower lobe consolidation and a right-sided pleural effusion.  The patient is started on the appropriate treatment, and a diagnostic thoracentesis is performed that shows an uncomplicated parapneumonic effusion.  When a sterile sample of the inflammatory exudate is experimentally introduced into normal human tissue, rapid neutrophil locomotion is observed.  Which of the following components of the exudate is most likely responsible for this observed effect?

Quizplus · Accepted Answer

11ec160b_37b4_7fbf_9249_f910f2c17322_MD0001_00 Parapneumonic effusions occur frequently in bacterial pneumonia as a result of exudative fluid accumulation within the pleural space. Infections and other forms of inflammatory tissue injury cause increased vascular permeability, leading to the formation of protein-rich exudates that contain a variety of biologically active substances. Under the influence of inflammatory stimuli, cell membrane phospholipids release arachidonic acid, a precursor to the eicosanoid inflammatory mediators (eg, prostanoids, leukotrienes, lipoxins). The most potent chemotactic eicosanoid is leukotriene B₄. In contrast, the cysteinyl-containing leukotrienes (eg, LTC₄, LTD₄, LTE₄) cause bronchospasm and increase bronchial mucus secretion and are important in asthma pathogenesis. (Choice A) Bradykinin is a component of the kinin system. It causes vasodilation, increases vascular permeability, stimulates smooth muscle contraction, and helps mediate pain. (Choice B) Complement components C3a, C4a, and C5a are inflammatory anaphylotoxins that trigger histamine release from mast cells, resulting in vasodilation and enhanced vascular permeability. C5a also recruits and activates neutrophils, monocytes, eosinophils, and basophils. C4a is the least active of these complement components and plays a minor role in leukocyte recruitment. (Choice C) Interferon gamma (IFN-γ) activates macrophages, increases MHC expression, and promotes T_H1 cell differentiation. It is produced primarily by activated T cells and natural killer cells. (Choice D) IL-4 is a cytokine produced by T_H2 cells that activates B cells, induces IgE isotype switching, and promotes T_H2 cell differentiation. (Choice F) Thromboxane A₂ is an eicosanoid synthesized by platelets that causes vasoconstriction and platelet aggregation. Educational objective: Leukotriene B₄ stimulates neutrophil migration to sites of inflammation. Other important chemotactic agents include 5-HETE (leukotriene precursor), complement component C5a, and IL-8.

A 68-Year-Old Man Comes to the Emergency Department with a 2-Day