B. mori Host Response to Bb A007987 A012866 pgrp-s2 pgrp-s5 A002739 A006775 A000039 A013865 A011495 attacin lebocin enbocin gloverin moricin .-300 .-002 .-100 .000 .010 .020 .030 Figure 9. Bb induced silkworm systemic immune response. (a)Bb can be recognized by short-type of peptidoglycan recognition proteins (PGRPs) PGRP-S2 and PGRP-S5, then, mainly through Toll signal pathway, antimicrobial peptide coding genes were induced (the asterisk indicated a family, for the probe can not distinguish a member out from highly homologous sequences). (b) Toll pathway signal transduction diagrammatic sketch and real time PCR ratios of corresponding genes. (c) JAK/STAT sinal transduction diagrammatic sketch and real time PCR ratios of corresponding genes. For a detailed view of the cluster ratios, see Table S4. doi:10.1371/journal.pone.0008098.g009 hosts showed that Buchnera have lost many capabilities, indicating that the host must compensate for gene losses and integrate symbiont functions into the mutualistic system [111]. However, the mechanisms of the basal metabolic pathways modulation for both host and pathogen are not exactly known, becoming a particularly intriguing question to investigate. Bb can produce spores and parasporal crystal. Therefore, it is thought to have similar pathogenicity to Bt, and a further study has confirmed this. Seven of the nine APNs showed substantial or modest upregulation from 3 hpi to 12 hpi. Three APNs for Bt toxins (A008017, A008060 and A008059) did not show the highest expression levels in this analysis, but did show modest upregula- tion. These results demonstrated the specific relationship between host APNs and pathogen toxins. However, at 24 hpi, all of the nine APNs showed downregulation. The SEM picture showed that toxins accumulated on intestinal epithelial cells and the midgut epithelial cells and microvillus had been damaged by the toxins. Thus, the infiltration balance was broken. In higher vertebrates, immunomodulator hormones such as glucocorticoids and growth hormones can communicate between the immune and nervous systems during infection [112]. In insects, although relationships between hormones and pathogens infection are rarely studied, insects can be regulated by JH during development and metamorphosis is well known [68]. Interestingly, JH biosynthesis- and metabolism-related genes were upregulated after the infection in this study. Also, many of these genes were PLoS ONE | www.plosone.org 13 December 2009 | Volume 4 | Issue 12 | e8098