Inflammation and Immune Pathology USMLE Step 1 Practice Question

A 44-year-old man presents with acute bacterial cellulitis of the left lower leg. Vital signs show BP 138/82 mmHg, HR 98/min, RR 16/min, temperature 38.2°C, and SpO2 98% on room air. Physical examination reveals erythema, warmth, and edema without fluctuance. WBC count is elevated at 14,200/μL with left shift. Tissue biopsy obtained early in the infection demonstrates dense neutrophilic infiltrate actively migrating toward the bacterial focus. Which complement product primarily mediates neutrophil chemotaxis in this acute inflammatory response?