The process by which leukocytes migrate toward a chemical signal at the site of injury is known as

• A. Chemotaxis
• B. Diapedesis
• C. Phagocytosis
• D. Opsonization

Answer: (A)

Chemotaxis is the directed movement of leukocytes toward higher concentrations of chemical signals released at the site of injury. This gradient guides immune cells, such as neutrophils, from the bloodstream into damaged tissue so they can confront invading pathogens. The cells sense the chemical cues—chemokines like IL‑8 and inflammatory mediators such as C5a—and polarize their motion toward the signal, effectively following the chemical trail to the wound. Once at the site, leukocytes may cross the endothelium in a process called diapedesis, and then engage in phagocytosis to ingest pathogens. Opsonization, meanwhile, marks pathogens with antibodies or complement to enhance their uptake, but it is not the migratory step itself.