Final answer:
Opsonins are molecules that coat pathogens and enhance phagocytosis by phagocytic cells, which possess receptors for these molecules. Complement proteins and antibodies like IgG are examples of opsonins. This process helps in the neutralization and elimination of pathogens.
Step-by-step explanation:
The molecule that coats a pathogen and stimulates phagocytosis by cells bearing receptors for that molecule is known as an opsonin. Opsonins, such as complement proteins, C-reactive protein, serum amyloid A, and IgG antibodies, play a crucial role in the immune response by marking pathogens for destruction. Phagocytes, including macrophages, dendritic cells, and neutrophils, have specific receptors that recognize and bind to these opsonins. This interaction enhances the ability of phagocytes to attach to, engulf, and digest the pathogen, thereby preventing it from causing an infection.
Pattern recognition receptors (PRRs) on macrophages and dendritic cells also bind to molecular signatures of pathogens, promoting their engulfment and destruction. Through the process of opsonization, antibodies coat extracellular pathogens and neutralize them, which can prevent the pathogens from infecting host cells. Neutralized pathogens can then be eliminated from the body through the spleen or excreted in urine or feces.