D3401: Mosquito pericardial cells express cecropin: Insignias of their immune functions

Despite numerous international initiatives, malaria continues to be the most significant tropical illness, accounting for 200 million infections and around 500,000 fatalities each year. Although there are many cases of malaria, only a small percentage of Anopheles mosquitoes become infected and spread the disease; because they have a robust immune response that protects them against many pathogens such as Plasmodium. Sporozoites produced in the oocyst from the midgut must reach the salivary glands for a mosquito to transmit disease, and they achieve this by taking advantage of the heart-controlled hemolymph flow. Recently the heart has been considered a key organ for the immune system because a tripartite interaction occurs there, hemocytes-heart-pathogens, which enhance the immune response. Pericardial cells (PCs), also called nephrocytes (for their scavenger functions), are accessory heart cells which has been involved in this tripartite interaction. Previous studies showed that PCs have antimicrobial properties, and express immune-related genes such as lysozymes and antimicrobial peptides. Here, we demonstrate that one of the principal sources of Cecropin 1 (Cec1) in the mosquito Anopheles albimanus is the heart. Moreover, we discovered that Cec1 is overexpressed in the heart following an immunological challenge. In addition, through a new molecular tool for detecting mRNA in situ (RNA FISH-STIC), we showed for the first time that PCs are the only cell type of heart expressing Cec1. These findings suggest that PCs can be a type of immune cell that could be determinant during the mosquito systemic immune response.