There are two ways: 1. cytoplasmic membrane receptors - when phagocytes only have receptors for components that are exclusively on bacterial surfaces. 2. opsonins - antimicrobial proteins that signal to the phagocyte.
Phagocytes are the soldiers of the immune system, and provide innate immunity. They are responsible for swallowing, killing and digesting invading microbes. The process of swallowing microbes is known as phagocytosis.
There are two main types of phagocyte:
Microphages
These cells are also known as Polymorphonuclear Leucocytes, PMNs and Polymorphs. These cells start life in the bone marrow. They are constantly circulating in the blood. They cannot replicate, and live for only a few days. The bone marrow contains large reserves of microphages.
Macrophages
These cells start out life as monocytes, which originate in the stem cells in the bone marrow, but when they are first called into action, they turn into macrophages. Macrophages are not as numerous as microphages, and there are no large reserves of them, but they are longer lived than microphages. Macrophages are stationed at strategic locations throughout the body, usually in places that are not otherwise well defended. These areas include the alveoli of the lungs, the abdominal (peritoneal) and chest (pleural) cavities, under the top layer of the skin and the intestines. Macrophages are the front line of defense against microbial invasion in these areas.
Learn more about phagocytes at Primer.crohn.ie and Boundless.com.