This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
The chemotactic factor is: 
Select and explain. 
A. C2a, B. C3b, C. C4a, D. C5a
D: C5a
Answer: D: C5a 
Explanation: C5a is a chemotactic molecule specifically recognized by polymorphonuclear leukocytes or phagocytic cells.
This substance causes leukocytes to migrate to a tissue in which an antigen–antibody reaction is taking place. 
At that site, a phagocytic cell recognizes opsonized particles and ingests them.
C5a not only has a chemotactic effect on neutrophils, but also activates these cells causing their reversible aggregation and release of stored enzymes, including proteases.
C5a also enhances the adhesiveness of neutrophils to the endothelium.

Parija SC. Textbook of Microbiology & Immunology. Elsevier Health Sciences; 2014. Page:120