These circulating cells also play an important role in the body’s defense against infection. These cells produce adhesin molecule receptors, permitting them to adhere to and migrate from the blood vessels to the site of infection. They are attracted to the site by IL-8, C3a and C3b, cytokines released by TH1 cells, and finally factors produced by mast cells. These cells are also phagocytic cells, and the process of phagocytosis is similar to that seen in macrophages. They are particularly effective when the invading organisms becomes coated with antigen-specific antibodies (often called opsonins) along with activated complement components.