Localization of the serine protease homolog BmSPH-1 in nodules of E. coli-injected Bombyx mori larvae and functional analysis of its role in nodule melanization

Hemolymph Melanization in the Silkmoth Bombyx mori Involves Formation of a High Molecular Mass Complex That Metabolizes Tyrosine

“…Where our data add new insights is where they indicate that Tyr usage is predominantly associated with a POcontaining complex that elutes in a fraction near a 670-kDa standard, and formation of this complex does not depend on quinone cross-linking. Our results further show that this POcontaining complex contains SPH1, as observed for the complexes reported from beetles (27,28) and very recently melanized nodules from B. mori (49). However, the B. mori complex we analyzed also consistently contains other proteins, including apolipophorins previously implicated as clotting factors in Drosophila (4), a lectin that could function as a PRR or binding protein, and a hexamerin, which is a protein that structurally resembles PO itself (1,2).…”

“…In addition, we never detected tyramine or DA in B. mori plasma in the first 20 min after collection from a wound site. Thus, although Tyr decarboxylase and DOPA decarboxylase have both been suggested to play roles in converting Tyr to tyramine and DOPA to DA for use by POs (49,(53)(54)(55), we see no evidence for this during the rapid melanization of B. mori plasma from a wound site.…”

Serratia marcescens Suppresses Host Cellular Immunity via the Production of an Adhesion-inhibitory Factor against Immunosurveillance Cells

“…Moreover, our results suggested that serralysin acts as a metalloprotease to degrade BmSPH-1, a factor involved in cellular immune responses, by mediating the adhesion of hemocytes to the tissue surface. Sakamoto et al (27) recently reported that activated BmSPH-1 localized within hemocyte aggregates when nodule formation is induced in silkworms infected by bacteria. Therefore, although BmSPH-1 is normally present in the hemolymph of noninfected silkworms, it is recruited to hemocyte surfaces after immunologic stress and contributes to cellular adhesion and melanization processes within the aggregates (27).…”

“…Sakamoto et al (27) recently reported that activated BmSPH-1 localized within hemocyte aggregates when nodule formation is induced in silkworms infected by bacteria. Therefore, although BmSPH-1 is normally present in the hemolymph of noninfected silkworms, it is recruited to hemocyte surfaces after immunologic stress and contributes to cellular adhesion and melanization processes within the aggregates (27). Based on our in vitro results, we considered that BmSPH-1 was activated through the hemocyte isolation process and recruited to cell surfaces and then degraded by recombinant serralysin, leading to the suppression of cellular immune responses.…”

“…5B). BmSPH-1 is involved in a cellular immune response called nodule formation, a process characterized as an aggregation of hemocytes that trap foreign substances and attach to internal tissues (27).…”