Extracellular vesicles secreted by Brugia malayi microfilariae modulate the melanization pathway in the mosquito host

Abstract

Vector-borne, filarial nematode diseases represent a significant and affecting disease burden in humans, domestic animals, and livestock worldwide. Parasitic filarial nematodes require both an intermediate (vector) host and a definitive (mammalian) host during the course of their life cycle. In either host, the nematode must evade the host elicited immune response in order to develop and establish infection. There is direct evidence of parasite-derived immunomodulation in mammals, however, there is less evidence of parasite immunomodulation of the vector host. We have previously reported that all life stages of Brugia malayi, a causative agent of lymphatic filariasis, secrete extracellular vesicles (EVs). Here we investigate the immunomodulatory effects of microfilariae derived EVs on the vector host Aedes aegypti. RNA-seq analysis of an A. aegypti cell line treated with B. malayi microfilariae EVs showed differential expression of both mRNAs and miRNAs, some with roles in immune regulation. One downregulated gene, AAEL002590, identified as a serine protease, was shown to have direct involvement in the phenoloxidase (PO) cascade through analysis of PO activity. Similarly, injection of adult female mosquitoes with B. malayi microfilariae EVs validated these results in vivo, eliciting a downregulation of the AAEL002590 transcript and a significant reduction in PO activity. Our data indicates that parasite-derived EVs are capable of interfering with critical immune responses in the vector host, particularly immune responses such as melanization that target extracellular parasites. In addition, this data provides novel targets for transmission control strategies for LF and other parasitic diseases. Author SummaryVector-borne, filarial nematode diseases represent a significant and affecting disease burden in humans, domestic animals and livestock worldwide. Parasitic nematodes must evade the elicited immune response of their hosts in order to develop and establish infection. While there is evidence for immunomodulation of the mammalian host, the mechanism of this immunomodulation is not fully clear and there is limited evidence for immunomodulation of the vector host. Here we have shown that parasite-derived extracellular vesicles are effector structures for immunomodulation of the vector host. In particular, we have identified that parasite-derived extracellular vesicles can interfere with critical mosquito immune responses against parasites. This data provides insight into parasite biology and novel targets for transmission control strategies for parasitic diseases.