Transcriptional Profiling of Midgut Immunity Figure 8. The immune deficiency (Imd) pathway may regulate antimicrobial peptides (AMPs) production in the midgut during the wandering stage. (A, B) All genes of the Imd pathway were up-regulated. (C) A few genes of the Toll pathway were also up-regulated. All others were not changed. Therefore, the Imd pathway might be the main pathway for regulating the production of AMP in the midgut during the wandering stage. doi:10.1371/journal.pone.0043769.g008 investigated these aspects by transcript profiling of the midgut during the wandering stage compared with the feeding stage. Normally, insect hemocytes and fat bodies produce antimicro- bial proteins when they are challenged by bacterial components [34,48]. In M. sexta, antimicrobial proteins produced in the wandering midgut kill bacteria according to the in vitro assay [18,19]. The insect midgut contains many bacteria that might induce the production of immunity related proteins during the wandering stages when the midgut is degenerating to give the resident midgut bacteria a chance to contact and challenge the Figure 9. Morphological changes of silkworm midguts during the wandering stage. (A–C) Comparison of the morphology of silkworm guts on the 3rd day of the fifth larval stage (A; V-3: 12 h), and 6 h (B; W: 6 h) and 24 h (C; W: 24 h) after the initiation of the wandering stage. (A–a, B–a and C–a) The whole gut is divided into foregut (FG), midgut (MG), and hindgut (HG). The arrowhead-indicated part of each midgut was sampled for histological study with haematoxylin and eosin which are shown in (b and c) of each panel. Each (b) is a picture with low magnification, and the white-dot-lined area is shown in (c) with high magnification. In (B–c), the arrow indicates a cell full of vesicles probably due to apoptosis. In (C–c), the arrow shows the detached midgut from the basement membrane. Bars: A–a, B–a and C–a: 4 mm; A–b, B–b and C–b: 100 mm; A–c, B–c and C–c: 50 mm. doi:10.1371/journal.pone.0043769.g009 PLOS ONE | www.plosone.org 10 August 2012 | Volume 7 | Issue 8 | e43769