Final answer:
Monocytes are the precursors to macrophages, and once they enter the tissues, they differentiate into macrophages that perform phagocytosis.
Step-by-step explanation:
The type of cell that circulates in the blood and lymph and differentiates into macrophages after moving into infected tissue is the monocyte. These cells are key players in the immune response. Once a monocyte enters the tissues, it transforms into a macrophage, which is capable of phagocytosis, the process of engulfing and destroying pathogens.
It's important to recognize that other cells like neutrophils, eosinophils, and dendritic cells also have phagocytic abilities. However, specifically, monocytes are the precursors that become macrophages in the tissues which not only phagocytize pathogens but can also produce chemicals that promote inflammation.