A hemocyte-like cell line established from the malaria vector Anopheles gambiae expresses six prophenoloxidase genes

Cell lines from the malaria vector Anopheles gambiae have been established as a tool for the study of the mosquito innate immune system in vitro. Here , we describe the first continuous insect cell line that produces prophenol oxidase (PPO), This cell line (4a-3B) expresses constitutively six PPO gene s, three of which are novel (PPO4, PPO5, and PPO6), The PPO genes show dist inct temporal expression profiles in the intact mosquito, spanning stages f rom the embryo to the adult in an overlapping manner. Transient induction o f larva-specific PPO genes in blood-fed adult females suggests that the dev elopmental hormone 20-hydroxyecdysone may be involved in PPO gene regulatio n. Indeed, exposure of 4a-3B cells to 20-hydroxyecdysone in culture results in induction of those PPO genes that are mainly expressed in early develop mental stages, and repression of PPO5, which is preferentially expressed at the adult stage. The cell line shows bacteria-induced immune transcripts t hat encode defensin and Gram-negative bacteria-binding protein, but no indu ction of PPO transcripts. This cell line most likely derives from a hemocyt e lineage, and represents an appropriate in vitro model for the study of th e humoral and cellular immune defenses of A. gambiae.