Final answer:
Inflammatory mediators secreted by macrophages lead to changes in ligand expression that allow neutrophils to adhere to endothelial cells and migrate to the site of the infection for efficient phagocytosis and pathogen clearance.
Step-by-step explanation:
The process by which inflammatory mediators secreted by macrophages change the ligand expression on neutrophils involves various steps of the immune response, particularly the inflammatory response. When tissue is injured, mast cells release histamines that cause vasodilation of nearby capillaries, which increases blood flow and capillary permeability. This allows plasma and leukocytes, such as neutrophils and monocytes that transform into macrophages, to enter the tissue space. Neutrophils, macrophages, and dendritic cells release chemicals that further stimulate inflammation. Macrophage-secreted cytokines modify the ligand expression on endothelial cells, facilitating neutrophil adhesion to the endothelium and their migration towards the site of infection, a process known as chemotaxis. This targeted migration enables neutrophils to reach the site of infection efficiently where they can perform phagocytosis to destroy pathogens.
The secretion of pro-inflammatory cytokines by macrophages at the site of infection or tissue damage is crucial for recruiting additional immune cells. These cytokines lead to changes in the expression of adhesion molecules on the endothelial cells, which act as ligands for neutrophil receptors. The modification in ligand expression allows neutrophils to bind more effectively to endothelial cells and pass through the blood vessel wall into the tissue—a process known as extravasation. Once in the tissue, neutrophils can engulf and digest pathogens through phagocytosis, thereby playing a critical role in containing and eliminating the infection.
Leukotrienes, another type of inflammatory mediator, are particularly effective at attracting neutrophils to the infection site through chemotaxis, enhancing the process of inflammation. Additionally, certain cytokines can have direct antimicrobial effects such as inhibiting protein synthesis in host cells. On a broader scale, inflammation results in the redness, swelling, heat, and pain that are characteristic of an inflammatory response, ultimately leading to healing and repair of the injured tissue.