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　　第??(di)一?(yi)道??(dao)防??(fang)御??(yu)是??(shi)物??(wu)理??(li)屏??(ping)障??(zhang)??，比??(bi)如??(ru)皮??(pi)膚??(fu)和??(he)黏??(nian)膜??(mo)??，像??(xiang)城??(cheng)墻??(qiang)一??(yi)樣??(yang)覆?(fu)蓋??(gai)體??(ti)表??(biao)??，通??(tong)過??(guo)汗??(han)液??(ye)、皮??(pi)脂??(zhi)和??(he)黏??(nian)液??(ye)中?(zhong)的??(de)抗??(kang)菌?(jun)成??(cheng)分?(fen)??，直??(zhi)接??(jie)阻??(zu)擋??(dang)細(xì)?(xi)菌??(jun)、病??(bing)毒??(du)入??(ru)侵??(qin)；比??(bi)如??(ru)呼?(hu)吸??(xi)道??(dao)纖??(xian)毛??(mao)??，如??(ru)同??(tong)護(hù)??(hu)城??(cheng)河??(he)的??(de)“清??(qing)道??(dao)夫??(fu)”??，通?(tong)過??(guo)擺??(bai)動(dòng)??(dong)??，將??(jiang)灰??(hui)塵?(chen)和??(he)病??(bing)原??(yuan)體??(ti)排??(pai)出??(chu)體??(ti)外??(wai)??。?　　B細(xì)??(xi)胞??(bao)作??(zuo)為??(wei)“抗??(kang)體??(ti)工??(gong)廠??(chang)”??，能??(neng)針??(zhen)對(duì)??(dui)不??(bu)同??(tong)病??(bing)原??(yuan)體??(ti)定??(ding)制??(zhi)特?(te)異??(yi)性??(xing)抗??(kang)體??(ti)??，通??(tong)過??(guo)中??(zhong)和??(he)病?(bing)毒??(du)或??(huo)標(biāo)??(biao)記??(ji)病??(bing)原??(yuan)體??(ti)協(xié)??(xie)助?(zhu)清??(qing)除?(chu)機(jī)??(ji)制??(zhi)；同??(tong)時(shí)??(shi)分??(fen)化??(hua)出??(chu)的??(de)記??(ji)憶??(yi)B細(xì)??(xi)胞??(bao)可??(ke)在??(zai)免?(mian)疫??(yi)結(jié)??(jie)束??(shu)后??(hou)保??(bao)留??(liu)抗?(kang)體??(ti)“圖??(tu)譜??(pu)”??，實(shí)??(shi)現(xiàn)??(xian)快??(kuai)速??(su)二??(er)次?(ci)應(yīng)??(ying)答??(da)??。??。