Fig. 2.

Drosophila antimicrobial autophagy in bacterial and viral infection. a L. monocytogenes is a Gram-positive bacterium that invades the cytoplasm. Intracellular bacteria are detected by the PRR PGRP-LE, which senses PGN derivatives that are components of the bacterial cell wall. PGRP-LE recognition activates several signaling pathways, including the activation of AMP production by the IMD and Jak-Stat signaling pathways, as well as autophagy. L. monocytogenes is found within autophagosomes, which mature and degrade the captured bacteria. The exact signaling pathway involved in triggering autophagy during L. monocytogenes infection remains to be determined, as canonical pathways such as the IMD and Toll pathways are not required. b VSV activates autophagy in flies likely through the viral glycoprotein VSV-G, which acts as a PAMP. Viral infection is sensed by the Toll receptor Toll-7, which localizes to the plasma membrane and binds to VSV virions. This binding is required to activate autophagy through an undefined signaling pathway (but is independent of the canonical Toll, IMD and Jak-Stat pathways). Previous research suggests that the nutrient signaling PI3K-Akt-TOR pathway, which typically constrains autophagy, is downregulated during VSV infection to trigger autophagy activation. It is still not understood exactly how autophagy restricts VSV replication, i.e. whether intact virions or viral proteins are captured by autophagosomes.