Fig. 8

Model showing CTL − Lys immune function regulates gut homeostasis and controls insect metamorphosis. CD209 and its downstream Lys1 maintain high expression levels in the midgut during the wandering stage due to the high 20E titers. Lys1 suppresses the proliferation of Lactobacillus in the midgut, resulting in a low abundance of Lactobacillus (and the associated PGN) in the hemocoel. In this condition, fat body cells are mainly involved in the storage of lipids and cholesterol esters in LDs, thus providing sufficient energy and 20E titers for timely pupariation. However, low expression levels of CD209 and Lys1 increase the Lactobacillus load in the midgut. The increased loads of Lactobacillus (and PGN) subsequently translocate into the hemocoel and trigger a shift from lipid storage to phospholipid synthesis. Moreover, cholesterol esters stored in LDs decrease. This leads to insufficient energy and 20E titers, thereby delaying pupariation. The low 20E titers, in turn, fail to induce high levels of CD209 and Lys1 expression in the midgut