Figure 5.

A model for how B. malayi microfilariae EVs interfere with the PO cascade and melanization. Melanotic encapsulation is a common insect defense mechanism against parasites. Upon recognition of a parasite, hemocytes aggregate forming a multicellular layer that deposits a melanin-enriched capsule around the invading parasite. Melanin production is controlled by the phenoloxidase (PO) cascade, which through a series of interdependent reactions, leads to the activation of PO that oxidizes phenols to quinones, which are further polymerized to melanin. Death of the parasite is believed to be due to nutrient deprivation, asphyxiation, or through the production of toxins such as quinones and other reactive oxygen species produced during melanin production. B. malayi microfilariae-derived extracellular vesicles downregulate a serine protease that functions either at the serine protease cascade or as a PPAF, either way interfering with the production of PO and thus inhibiting melanization of invading parasites. Image was created with Biorender.com.