How does the immune system work together with the circulatory system to function properly? a. the infection site receives oxygen-depleted blood from the circulatory system's arteries, so the immune system works harder. b. pathogens released by immune cells cause increased blood flow to the infection site, which brings other pathogens to the area more quickly. c. red blood cells move through the body (to parts where they are needed) in the blood vessels of the circulatory system to fight infection. d. the white blood cells of the immune system fight and destroy pathogens.