The chemotactic factor is:

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