TLR4 and infection: Two distinct pathways, the Toll pathway and Immune Deficiency (IMD) pathway, mediate the secretion of antimicrobial peptides in Drosophila. Infections mainly due to fungal and Gram-positive bacterial attack activate the Toll pathway, whereas the IMD pathway is activated, predominantly, in response to infections by Gram-negative and other Gram-positive bacteria [19, 20].