Monocytes are innate blood cells that maintain vascular homeostasis and are early responders to pathogens in acute infections.
Classical monocytes are critical for the initial inflammatory response. Classical monocytes can differentiate into macrophages in tissue and can contribute to chronic disease. Nonclassical monocytes have been widely viewed as anti-inflammatory, as they maintain vascular homeostasis. They are a first line of defense in recognition and clearance of pathogens.
(Source: Narasimhan 2019)