Phagocytosis is a mechanism of the innate immune response. Describe three cells who are responsible for phagocytosis and describe what triggers each to respond. Describe how two other aspects of the immune response can enhance phagocytosis. What role do phagocytes play in initiating the adaptive immune response?
The innate immune response reduces the workload of the adaptive immune response by preventing entry and spread of microorganisms in the body. The first line of defense is the external body membrane - intact skin and mucosae. The second line of defense is called into action when the first line of defense has been penetrated, using antimicrobial proteins and phagocytes. A phagocyte engulfs matter the way an amoeba ingests a food particle.
Three cells that are responsible for phagocytosis are monocytes, neutrophils, and eosinophils. The major phagocytes are macrophages, which derive from white blood cells called monocytes that leave the bloodstream, enter the tissues, and develop into macrophages.
When chemicals released by immune cells stimulate them, additional enzymes are activated that produce the respiratory burst, an event that liberates a flood of free radicals that have potent cell-killing ability. Monocytes take about 12 hours to differentiate and there are a lot of them. Neutrophils become phagocytic on encountering infectious materials in the tissues. Neutrophils are small but numerous and increase during acute infection (especially bacterial), secreting enzymes and producing antibiotic-like chemicals called defensins, that pierce the pathogen's membrane and destroy the neutrophils in the process. Eosinophils are weakly phagocytic and are fewer, but they are important in defending the body against parasitic worms. When they encounter parasitic worms, the eosinophils discharge the contents of their large cytoplasmic granules all over their prey.
Two other aspects of the immune response that can enhance phagocytosis are adherence and opsonization. In order for a...