Kinetic effects of cations and heat-labile opsonin. Tunicate intelectin is an opsonin for phagocytosis by hemocyte. The molecular mechanisms facilitating opsonin-dependent phagocytosis are different for specific opsonin/receptor pairs. They also express receptors to detect and adhere to endothelium and Fc receptors for opsonin. However, IgM is extremely efficient at activating complement and is, therefore, considered an opsonin. Opsonization involves the binding of an opsonin (e.g., antibody) to an epitope on a pathogen. They include opsonin receptors, scavenger receptors, and Toll-like receptors. After opsonin binds to the membrane, phagocytes are attracted to the pathogen. Opsonin Pharma Ltd. (OPL) produce and markets generic medicines for human use. Opsonin Pharma Limited is a pharmaceutical company in Bangladesh which was established in 1956.