3.气道上皮分泌抗微生物活性物质气道上皮具有分泌抗微生物活性物质，溶菌酶、分泌型免疫球蛋白A，肺表面活性物质蛋白A、D、乳铁蛋白等，通过溶菌、中和、调理等作用，直接或间接抑制病原体侵袭，对气道上皮起保护作用。
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