From the Laboratory of Microbiology, Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo 113-0033, Japan.
J Biol Chem. 2014 Feb 28;289(9):5876-88. doi: 10.1074/jbc.M113.544536. Epub 2014 Jan 7.
Injection of a culture supernatant of Serratia marcescens into the bloodstream of the silkworm Bombyx mori increased the number of freely circulating immunosurveillance cells (hemocytes). Using a bioassay with live silkworms, serralysin metalloprotease was purified from the culture supernatant and identified as the factor responsible for this activity. Serralysin inhibited the in vitro attachment of both silkworm hemocytes and murine peritoneal macrophages. Incubation of silkworm hemocytes or murine macrophages with serralysin resulted in degradation of the cellular immune factor BmSPH-1 or calreticulin, respectively. Furthermore, serralysin suppressed in vitro phagocytosis of bacteria by hemocytes and in vivo bacterial clearance in silkworms. Disruption of the ser gene in S. marcescens attenuated its host killing ability in silkworms and mice. These findings suggest that serralysin metalloprotease secreted by S. marcescens suppresses cellular immunity by decreasing the adhesive properties of immunosurveillance cells, thereby contributing to bacterial pathogenesis.
向家蚕血液中注射粘质沙雷氏菌的培养液上清，可增加游离循环免疫监视细胞（血细胞）的数量。通过对活家蚕的生物测定，从培养液上清中纯化出丝氨酸蛋白酶 Serralyisin，并将其鉴定为具有这种活性的因子。Serralyisin 抑制家蚕血细胞和鼠腹腔巨噬细胞的体外黏附。用 Serralyisin 孵育家蚕血细胞或鼠巨噬细胞，分别导致细胞免疫因子 BmSPH-1 或钙网蛋白的降解。此外，Serralyisin 抑制血细胞的体外细菌吞噬作用和家蚕体内细菌清除作用。在粘质沙雷氏菌中破坏 ser 基因，可减弱其在家蚕和小鼠中的宿主杀伤能力。这些发现表明，粘质沙雷氏菌分泌的丝氨酸蛋白酶 Serralyisin 通过降低免疫监视细胞的黏附特性来抑制细胞免疫，从而有助于细菌发病机制。
