A 43-year-old man has a 1-day history of fever and increasing headache, irritability, photophobia, and lethargy. Physical examination shows neck stiffness. Cerebrospinal fluid (CSF) shows 76,000 neutrophils/mm3, occasionally with intracytoplasmic gram-positive cocci. Which of the following substances is most responsible for the CSF neutrophil count?
Bradykinin
C5a
Factor XII (Hageman factor)
Histamine
Leukotriene E4
Correct answer
C5a
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correct answer: B
C5a is the major factor responsible for neutrophil chemotaxis. Activation of both the classical and alternative complement pathways results in C5a production and eventual membrane attack complex (MAC) formation.