Is the superantigenic activity required for the emetic activity of staphylococcal enterotoxin A

葡萄球菌肠毒素A （SEA）是一种由金黄色葡萄球菌产生的细胞外蛋白。SEA表现出催吐活性和超抗原活性。SEA的催吐作用机制尚不清楚。在本研究中，我们证明了以下结果：通过位点定向诱变，在SEA的t细胞受体和MHC II类分子结合区进行了突变。我们制备了13个SEA （mSEA）突变蛋白。我们检测了mSEAs在人外周血白细胞（HPBL）和麝香鼩脾细胞（Suncus murinus）中的超抗原活性。此外，我们通过腹腔注射比较了这些mSEAs的诱导呕吐活性。所有mSEAs均与抗sea抗体反应。包括N25G、F47G、C96G、C106A、V174G和D227A在内的mSEAs的超抗原活性不足，因为这些突变蛋白的细胞增殖和诱导的IL-2、IFN-γ和TNF-α在HPBL中减少。F47G、F47S、C96G、C106A、V174G和D227A的mSEA均降低了麝香脾细胞的增殖活性。F47G、F47S、H61D、H187A和D227A对家蝇的催乳活性降低。这些结果表明，SEA分子上的F47和D227位点对超抗原和诱导呕吐活性都是必需的，而H61、H187和H225位点对诱导呕吐活性都是必需的，并且超抗原和诱导呕吐活性的活性位点可能不同。

Staphylococcal enterotoxin A (SEA) is an extracellular protein produced by Staphylococcus aureus. SEA shows emetic activity and superantigenic activity. The mechanism of emetic activity of SEA has been little known. In the present study, we demonstrated the following results:Mutation was carried out at sites of T-cell receptor- and MHC class II molecule-binding regions on SEA by site-directed mutagenesis. We prepared 13 mutant SEA (mSEA) proteins. We examined superantigenic activities of mSEAs in human peripheral blood leukocytes (HPBL) and spleen cells of house musk shrews (Suncus murinus). Moreover, we compared emesis-inducing activities among these mSEAs by intraperitoneal injection. All mSEAs reacted with anti-SEA antibody. Superantigenic activities of mSEAs including N25G, F47G, C96G, C106A, V174G and D227A were deficient because cell proliferation and induction of IL-2, IFN-γ and TNF-α in HPBL were reduced in these mutant proteins. Activities of cell proliferation to spleen cell of house musk shew were reduced in mSEA including F47G, F47S, C96G, C106A, V174G and D227A. Emesis-inducing activities to house musk shew were reduced in F47G, F47S, H61D, H187A and D227A. These results suggest that sites of F47 and D227 on a SEA molecule are essential for both superantigenic and emesis-inducing activities and of H61, H187 and H225 for emesis-inducing activity and that active sites for superantigenic and emesis-inducing activities may be different.