Final answer:
Monocytes are a type of white blood cell with indented or horseshoe-shaped nuclei, part of the agranulocyte group, and involved in immune responses as they differentiate into macrophages to combat infection.
Step-by-step explanation:
Monocytes are a type of white blood cell that play an important role in the immune system.
They are part of the agranulocyte group, originating from myeloid stem cells, and are recognized by their large size ranging from 12-20 µm and distinctly shaped nuclei.
Monocytes typically have indented or horseshoe-shaped nuclei, which distinguishes them from other types of leukocytes such as neutrophils or lymphocytes that may have multi-lobed or more rounded nuclei.
When monocytes leave the bloodstream and enter body tissues, they differentiate into macrophages, which help phagocytize debris and foreign pathogens, as well as release chemicals that attract other immune cells to sites of infection.