Shepherd V L, Abdolrasulnia R, Garrett M, Cowan H B
VA Medical Center, Nashville, TN 37212.
J Immunol. 1990 Sep 1;145(5):1530-6.
We have investigated the effects of LPS and PMA on the expression of functional mannose receptors in rat bone marrow-derived macrophages. After 48 h of treatment with LPS (10 ng/ml) and PMA (100 nM), mannose receptor activity was reduced by 70 to 80%. The effect of these agents on receptor activity was not reversible, and activity continued to decline after the agents were removed. Pretreatment of cells with dexamethasone was effective in blocking the LPS/PMA-induced down-regulation. Serine protease inhibitors did not block the reduction in receptor activity, suggesting that proteolysis is not involved in receptor down-regulation. LPS/PMA treatment did not increase turnover of the receptor. Ligand uptake studies showed that the total capacity of the uptake system was reduced by 80%, although the Kuptake was unaffected. Binding of 125I-mannose-BSA to intact macrophages showed a 70% decrease in surface receptor activity after treatment with LPS/PMA. LPS/PMA treatment had no effect on total receptor synthesis as quantitated by immunoprecipitation of metabolically labeled receptor. However, binding of metabolically labeled receptor to mannose-Sepharose, and binding of 125I-mannose-BSA to immunoprecipitated receptor revealed that intracellular plus surface binding sites were reduced to approximately 30% after LPS/PMA treatment. These results suggest that LPS/PMA treatment of macrophages results in an inactivation of mannose receptors with no effect on receptor turnover or biosynthesis.
我们研究了脂多糖（LPS）和佛波酯（PMA）对大鼠骨髓来源巨噬细胞中功能性甘露糖受体表达的影响。用LPS（10 ng/ml）和PMA（100 nM）处理48小时后，甘露糖受体活性降低了70%至80%。这些试剂对受体活性的影响是不可逆的，去除试剂后活性仍继续下降。用地塞米松预处理细胞可有效阻断LPS/PMA诱导的下调。丝氨酸蛋白酶抑制剂不能阻断受体活性的降低，这表明蛋白水解不参与受体下调。LPS/PMA处理并未增加受体的周转。配体摄取研究表明，尽管摄取常数（Kuptake）未受影响，但摄取系统的总容量降低了80%。用LPS/PMA处理后，完整巨噬细胞上125I-甘露糖-牛血清白蛋白（125I-mannose-BSA）的结合显示表面受体活性降低了70%。通过代谢标记受体的免疫沉淀定量分析，LPS/PMA处理对总受体合成没有影响。然而，代谢标记受体与甘露糖-琼脂糖的结合，以及125I-甘露糖-BSA与免疫沉淀受体的结合表明，LPS/PMA处理后细胞内加表面结合位点减少至约30%。这些结果表明，LPS/PMA处理巨噬细胞会导致甘露糖受体失活，而对受体周转或生物合成没有影响。
