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　　嬰??(ying)幼??(you)兒??(er)期??(qi)(0～3歲??(sui))?，新??(xin)生??(sheng)兒??(er)免??(mian)疫??(yi)系??(xi)統(tǒng)??(tong)像??(xiang)一?(yi)支??(zhi)未??(wei)經(jīng)??(jing)實(shí)??(shi)戰(zhàn)??(zhan)的??(de)“新??(xin)兵??(bing)部??(bu)隊??(dui)”?，先??(xian)天??(tian)性??(xing)免??(mian)疫??(yi)(如??(ru)中??(zhong)性??(xing)粒??(li)細(xì)?(xi)胞??(bao)、巨??(ju)噬??(shi)細(xì)??(xi)胞??(bao))活??(huo)性??(xing)高?(gao)?，但??(dan)皮??(pi)膚??(fu)、黏??(nian)膜??(mo)屏??(ping)障??(zhang)薄??(bo)弱??(ruo)?，易??(yi)受??(shou)病??(bing)毒??(du)(如??(ru)呼??(hu)吸??(xi)道?(dao)合??(he)胞?(bao)病??(bing)毒??(du)、輪??(lun)狀??(zhuang)病??(bing)毒??(du))侵??(qin)襲??(xi)??。??此??(ci)時??(shi)主??(zhu)要??(yao)依??(yi)賴??(lai)母??(mu)體??(ti)通??(tong)過?(guo)胎?(tai)盤??(pan)和??(he)母??(mu)乳??(ru)傳??(chuan)遞??(di)的??(de)抗??(kang)體??(ti)(如??(ru)IgG、IgA)提?(ti)供??(gong)保??(bao)護(hù)?(hu)??。　　總??(zong)的??(de)來??(lai)說??(shuo)??，先?(xian)天??(tian)性??(xing)免??(mian)疫??(yi)的?(de)特??(te)點(diǎn)??(dian)是??(shi)反??(fan)應(yīng)??(ying)快??(kuai)、無??(wu)差??(cha)別??(bie)攻?(gong)擊??(ji)??，但??(dan)缺?(que)乏?(fa)“記??(ji)憶??(yi)功??(gong)能??(neng)”??，無??(wu)法?(fa)針??(zhen)對??(dui)特??(te)定??(ding)敵??(di)人?(ren)提??(ti)升??(sheng)戰(zhàn)??(zhan)斗?(dou)力??(li)??。??。