Oligopeptide Transporters of the SLC15 Family Are Dispensable for Peptidoglycan Sensing and Transport in Drosophila.

Peptidoglycan (PGN) detection by PGN recognition proteins (PGRP) is the main trigger of the antibacterial immune response in Drosophila. Depending on the type of immune cell, PGN can be sensed either at the cell membrane by PGRP-LC or inside the cell by PGRP-LE, which plays a role similar to that of Nod2 in mammals. Previous work, mainly in cell cultures, has shown that oligopeptide transporters of the SLC15 family are essential for the delivery of PGN for Nod2 detection inside of the cells, and that this function might be conserved in flies. By generating and analyzing the immune phenotypes of loss-of-function mutations in 3 SLC15 Drosophila family members, we tested their role in mediating PGRP-LE-dependent PGN activation. Our results show that Yin, CG2930, and CG9444 are required neither for PGRP-LE activation by PGN nor for PGN transport from the gut lumen to the insect blood. These data show that, while intracellular PGN detection is an essential step of the antibacterial response in both insects and mammals, the types of PGN transporters and sensors are different in these animals.