Similarly to BmToll9-1, BmToll9-2 Is a Positive Regulator of the Humoral Immune Response in the Silkworm, Bombyx mori

Toll receptors play important roles in the development and innate immunity of insects. Previously, we reported the immunological function of <i>BmToll9-2</i> in silkworm, <i>Bombyx mori</i>, larvae. In this study, we focused on the role of <i>BmToll9-2</i> as a regulator in the Toll signaling pathway. The expressions of most signaling genes in the Toll pathway, as well as immune effectors, were reduced after the RNAi of <i>BmToll9-2</i>. Coincidentally, hemolymph from <i>BmToll9-2</i>-silenced larvae exhibited decreased antibacterial activity in the growth of <i>Escherichia coli</i>, demonstrated either by growth curve or inhibitory zone experiments. The oral administration of heat-inactivated <i>E. coli</i> and <i>Staphylococcus aureus</i> following the RNAi of <i>BmToll9-2</i> up-regulated the expression of most signaling genes in the Toll pathway and downstream immune effectors. The above results indicate that <i>BmToll9-2</i> is positively involved in the Toll signaling pathway. As a positive regulator, <i>BmToll9-2</i> is shown to be activated preferentially against <i>E. coli</i> and, in turn, positively modulates the humoral immune response in antibacterial activity.