Immune activation upregulates lysozyme gene expression in Aedes aegypti mosquito cell culture

After stimulation with heat-killed bacteria, cultured cells from the mosquito Aedes aegypti (Aag-2 cells) secreted an induced protein with a mass of approximately 16 kDa that cross-reacted with antibody to chicken egg lysozyme. To investigate whether lysozyme messenger RNA is induced in bacteria-treated cells, we used polymerase chain reaction-based approaches to obtain the complete lysozyme cDNA from Aag-2 cells. The deduced protein contained 148 amino acids, including a 23 amino acid signal sequence. The calculated mass of the precursor protein is 16 965 Da, which is processed to yield a mature lysozyme of 14 471 Da with a calculated pI of 10.1. The lysozyme from Ae. aegypti shared 50% amino acid identity with lysozymes from Anopheles gambiae and Anopheles darlingi, which in turn shared 70% identity between each other. Northern analysis with the lysozyme cDNA probe showed induction of a 1.3 kb messenger RNA during the first 3 h after treatment of Aag-2 cells with heat-killed bacteria, followed by maximal expression 12-36 h after treatment. Southern analysis suggested that the gene likely occurs as a single copy in the genome of Aag-2 cells.