Final answer:
Mononuclear cells like monocytes and macrophages are integral to the body's immune system. Monocytes perform phagocytosis and antigen presentation, while macrophages are involved in immune defense and tissue repair, in addition to their phagocytic activities.
Step-by-step explanation:
Mononuclear cells comprise various types of white blood cells that have a single nucleus. Among these are monocytes and macrophages, which play crucial roles in the immune system. Monocytes, which develop from myeloid stem cells, typically make up 2-8 percent of the leukocyte count. They are recognized by their large size of 12-20 µm and unique indented nuclei. Their primary functions include phagocytosis and antigen presentation. Macrophages are differentiated monocytes that have exited the bloodstream. They are key players in immune defense and tissue repair, engaging in the phagocytosis of various entities such as pathogens and dead cells. Furthermore, they release antimicrobial substances and cytokines that attract additional immune cells to sites of infection, playing a critical role in body's defense mechanisms.