Binding of Clostridium difficile toxin A to human milk secretory component
Binding of Clostridium difficile toxin A to human milk secretory component
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DOI：
10.1099/00222615-47-10-879
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发表时间：
1998-10-01
影响因子：
3
通讯作者：
Rolfe, RD
中科院分区：
文献类型：
--
作者：
Dallas, SD;Rolfe, RD
产毒艰难梭菌是从大多数健康的人类婴儿中分离出来的。无症状定植的确切机制尚不清楚；然而，该实验室先前的研究表明，人类乳汁中免疫球蛋白和非免疫球蛋白部分的成分都与毒素A结合，并阻止其与仓鼠肠道刷状缘膜(BBM)的相互作用。分泌型免疫球蛋白(SIgA)是母乳中发现的主要免疫球蛋白。由于SIgA在婴儿胃中抵抗消化，并以高水平进入结肠，其结合毒素A的能力是本研究的主题。纯化的SIgA抑制毒素A与纯化的BBM受体的结合，加热至100℃作用5min不影响其抑制活性。IGM、Ig G和血清Ig A对毒素A与BBM受体的结合无明显抑制作用，SDS-PAGE将SIgA主要分为三条主带：分泌组分、重链和轻链。放射性标记毒素A的放射自显影显示毒素A与SIgA的分泌成分(SC)结合，当SIgA的三个亚基被包被在微量滴定孔上时，SC与毒素A的结合明显多于SIgA的重链和轻链，纯化的SC也以与SIgA相似的剂量依赖的方式抑制毒素与受体的结合，SIgA的重链和轻链不抑制毒素A受体的结合。通过酶消化去除SIgA和SC中的碳水化合物，表明毒素A与脱糖的SC的结合比与糖基化的SC的结合要少得多。这些数据表明，母乳中的SC与毒素A结合，可能作为一种受体类似物发挥作用，保护人类婴儿免受艰难梭菌相关疾病的侵袭。
Toxigenic Clostridium difficile is isolated from a majority of healthy human infants. The exact mechanism of asymptomatic colonisation is unclear; however, previous studies in this laboratory have shown that components of both the immunoglobulin and nonimmunoglobulin fractions of human milk bind to toxin A and prevent its interaction with hamster intestinal brush border membranes (BBMs). Secretory IgA (sIgA) is the primary immunoglobulin found in human milk. As sIgA resists digestion in the infant stomach and passes at high levels into the colon, its ability to bind toxin A was the subject of this investigation. Purified sIgA in concentrations at and below those found in human milk inhibited the binding of toxin A to purified BBM receptors, Heating sIgA to 100 degrees C for 5 min did not affect its inhibitory activity. IgM, IgG and serum IgA did not appreciably inhibit the binding of toxin A to BBM receptors, SDS-PAGE separated sIgA into three major bands: secretory component, heavy chains and light chains. Autoradiography with radiolabelled toxin A revealed that toxin A bound to the secretory component (SC) of sIgA, When the three purified subunits of sIgA were coated on to microtitration wells, SC bound significantly more toxin A than the heavy or light chains of sIgA, Purified SC also inhibited toxin binding to receptors in a dose-dependent fashion similar to sIgA, The heavy and light chains of sIgA did not inhibit toxin A receptor binding. Removing carbohydrates from sIgA and SC by enzymic digestion showed that toxin A binds much less to deglycosylated SC than to glycosylated SC. These data suggest that SC in human milk binds to toxin A and may function as a receptor analogue, protecting human infants against C. difficile-associated disease.