武巧珍綜述 胡婭莉周乙華審校
(1.南京醫(yī)科大學(xué)附屬南京明基醫(yī)院,江蘇南京 210019;2.南京大學(xué)醫(yī)學(xué)院附屬鼓樓醫(yī)院,江蘇南京210008)
新生兒母源性抗體的免疫保護(hù)以及對疫苗接種的影響
武巧珍1綜述 胡婭莉2周乙華2審校
(1.南京醫(yī)科大學(xué)附屬南京明基醫(yī)院,江蘇南京 210019;2.南京大學(xué)醫(yī)學(xué)院附屬鼓樓醫(yī)院,江蘇南京210008)
母源性抗體是指嬰幼兒或新生兒通過胎盤或乳汁從母體所獲得的抗體。新生兒可通過乳汁獲得特異性分泌型Ig A(secretory Immunoglobulin A,sI-g A)[1],但是通過胎盤獲得的特異性免疫球蛋白G(Immunoglobulin G,IgG)仍是母源性抗體的主要成分。母源性抗體能保護(hù)新生兒和嬰幼兒抵御相應(yīng)病原體的感染,但也可影響嬰幼兒疫苗接種后主動免疫應(yīng)答。了解母源性抗體轉(zhuǎn)運(yùn)特征,對理解新生兒對病原體的免疫以及預(yù)防接種具有重要意義。
哺乳動物胎盤的絨毛膜上皮可特異性傳遞IgG,其過程由新生兒Fc受體(neonatal Fc receptor,F(xiàn)cRn)介導(dǎo)[2]。孕早期僅有少量母體IgG轉(zhuǎn)運(yùn)到胎兒,隨著胎齡增加,胎兒IgG水平也相應(yīng)增加。雖然有報道新生兒體內(nèi)母源性抗體水平與其母親基本一致,例如呼吸道合胞病毒母源性抗體的母胎轉(zhuǎn)運(yùn)率為1.01[3],新生兒體內(nèi)母源性甲型肝炎抗體水平也與母親的濃度相近[4],但大多數(shù)足月兒母源性抗體的滴度明顯高于母體水平[5]。對乙型肝炎表面抗體(抗-HBs)陽性孕婦及其足月分娩的子女研究顯示,新生兒臍血抗-HBs幾何平均濃度為195.4 mIU/ml,明顯高于其母親的141.6 mIU/ml,其中81.0%的新生兒抗-HBs水平高于母親[6]。對巨細(xì)胞病毒抗體(CMV IgG)陽性孕婦以及足月兒的研究表明,新生兒臍血CMV IgG平均濃度為770.35 IU/ml,明顯高于其母親抗體的654.20 IU/ ml,其中64.82%的新生兒CMV Ig G水平高于母親[7]。對破傷風(fēng)抗體及抗白喉類毒素抗體陽性孕婦以及足月分娩新生兒觀察顯示,新生兒臍血破傷風(fēng)抗體及抗白喉類毒素抗體平均濃度分別為1.17 IU/ml和0.61 IU/ml,高于其母親抗體的0.88 IU/ml和0.56 IU/ml,該兩種抗體的母胎轉(zhuǎn)運(yùn)率分別高達(dá)1.75和1.5[8]。足月新生兒母源性麻疹抗體、呼吸道合胞病毒抗體、百日咳抗體等亦高于母體水平[9,10]。
早產(chǎn)兒母源性IgG胎盤轉(zhuǎn)運(yùn)率較足月兒低,如麻疹抗體、風(fēng)疹抗體、單純皰疹病毒抗體、腮腺炎抗體、B型流感嗜血桿菌抗體、脊髓灰質(zhì)炎抗體、白喉抗體、百日咳抗體和破傷風(fēng)抗體[11]。Linder等[12]發(fā)現(xiàn)在孕齡較小的早產(chǎn)兒中,母源性麻疹抗體、風(fēng)疹抗體和水痘帶狀皰疹病毒抗體水平都低于孕齡較大的早產(chǎn)兒。而32~36周早產(chǎn)兒的母源性腮腺炎抗體、麻疹抗體、風(fēng)疹抗體和單純皰疹病毒抗體水平接近母體水平[13],對45例破傷風(fēng)抗體及抗白喉類毒素抗體陽性孕婦及其早產(chǎn)新生兒研究顯示,早產(chǎn)兒臍血破傷風(fēng)抗體及抗白喉類毒素抗體平均濃度分別為0.81 IU/ml和0.44 IU/ml,與其母親的0.80 IU/ml和0.47 IU/ml相似。
IgG的4種亞型均可通過胎盤,但其通過率不同。IgG1和IgG4轉(zhuǎn)運(yùn)率高于IgG3,IgG2轉(zhuǎn)運(yùn)率最低。其機(jī)制可能是胎盤絨毛間質(zhì)的巨噬細(xì)胞表達(dá)的3種IgG FcR,即FcRI、FcRII和FcRIII與不同IgG亞型結(jié)合的親和力不同而致。因此,免疫誘導(dǎo)產(chǎn)生的IgG亞型不同,其胎盤轉(zhuǎn)運(yùn)效率亦不同。多糖疫苗主要誘導(dǎo)產(chǎn)生IgG2,如MenC和Hib疫苗[14];而蛋白疫苗主要誘導(dǎo)產(chǎn)生IgG1和IgG3,如白百破疫苗[15]。Einarsdottir等[16]研究發(fā)現(xiàn),IgG3的半衰期由435位點(diǎn)單個氨基酸多態(tài)性決定,G3m16(+)人群表達(dá)H435-IgG3,半衰期21天,胎盤對其轉(zhuǎn)運(yùn)效率與IgG1相似;G3m16(-)人群表達(dá)R435-IgG3,半衰期只有7天,其胎盤轉(zhuǎn)運(yùn)效率明顯低于H435-IgG3。IgG1激活補(bǔ)體和引起細(xì)胞毒性作用的能力最強(qiáng),一般認(rèn)為,新生兒出生時IgG1抗體水平高,可以保護(hù)新生兒避免感染的時間長,效果好。
特異性IgG母胎轉(zhuǎn)運(yùn)效率與母體總IgG濃度有關(guān)。如果母體總IgG濃度高,其他特異性IgG母胎轉(zhuǎn)運(yùn)相應(yīng)減少[17],這可能由于胎盤FcR數(shù)量有限,IgG競爭性與FcRn結(jié)合才能通過胎盤有關(guān)。母體特異性IgG抗體濃度高,則抗體轉(zhuǎn)運(yùn)率高,如麻疹自然感染的母親的麻疹I(lǐng)gG抗體高于免疫接種后產(chǎn)生的抗體,前者的新生兒的麻疹抗體也高于后者的新生兒[12]。
母親營養(yǎng)狀況也影響抗體的母胎轉(zhuǎn)運(yùn)。Wesumperuma等[18]發(fā)現(xiàn)無貧血的母親及其新生兒的破傷風(fēng)、白喉、帶狀皰疹病毒抗體比貧血母親及其新生兒高,Baba等也發(fā)現(xiàn)無貧血母親及其新生兒麻疹抗體較貧血的母親及新生兒高。高血糖孕婦血漿中IgG水平低于血糖正常孕婦,但是其新生兒臍血中IgG水平則高于血糖正常孕婦的新生兒[19]。此外,母胎抗體轉(zhuǎn)運(yùn)與產(chǎn)次、母親年齡、母親體重、母親身高無關(guān)。
某些慢性感染可影響母源性抗體轉(zhuǎn)運(yùn)至胎兒。HIV、瘧疾感染可影響母胎抗體轉(zhuǎn)運(yùn),可能因其損害胎盤FcR功能所致?;集懠驳哪赣H,其百日咳IgG和B型流感嗜血桿菌IgG胎盤轉(zhuǎn)運(yùn)減少,HIV感染影響麻疹抗體、肺炎球菌抗體的母胎轉(zhuǎn)運(yùn)[20-22]。暴露于HIV但未發(fā)生感染的新生兒,母源性B型流感嗜血桿菌IgG濃度較正常新生兒的低[23]。Moro等[24]對187例瘧疾和HIV感染的孕婦及其新生兒研究發(fā)現(xiàn),這兩種感染可減少瘧疾抗體的胎盤轉(zhuǎn)運(yùn)。Jones等[25]對HIV感染孕婦及其未感染的新生兒研究顯示,HIV感染可使百日咳抗體、B型流感嗜血桿菌抗體、肺炎球菌抗體、破傷風(fēng)抗體的母胎轉(zhuǎn)運(yùn)率明顯降低,分別是未感染HIV孕婦胎盤轉(zhuǎn)運(yùn)率的58%、61%、28%和32%。
母源性抗體隨新生兒年齡增長而下降,其衰減率因抗體種類不同而異。嬰兒體內(nèi)不同的母源性IgG半衰期不盡相同,約為21~51天。母源性抗-HBs的衰減在小鼠實(shí)驗(yàn)中顯示,前4周快速下降,之后趨緩至11周齡轉(zhuǎn)陰。在足月新生兒中,1月齡下降36%,推測母源性抗-HBs衰減半衰期約41天[6]。母源性CMV抗體出生時、1月齡、3.5月齡時分別為843 IU/ml、454 IU/ml、75 IU/ml,到8月齡時均消失[7]。103例臍血百日咳抗體濃度60.1 IU/ml,出生后5天、1月、2月時抗體濃度分別為40.6 IU/ml、20.7 IU/ml、16.7 IU/ml[26]。母源性呼吸道合胞病毒抗體的半衰期在荷蘭和美國為21~16天,在肯尼亞為79天,而在發(fā)展中國家約30天[3]。在嬰幼兒體內(nèi),母源性麻疹抗體的半衰期為40~64天,中和抗體的半衰期為46.1~60.8天,衰減速度前幾個月較快,隨后減慢,出生后7~9個月即降至最低[27]。Brinkhof等[4]根據(jù)99例嬰兒母源性甲肝抗體的衰減推算其半衰期約40天,95%嬰兒的母源性甲肝抗體可持續(xù)13.2個月。
因母源性IgG抗體可以高效通過胎盤進(jìn)入胎兒體內(nèi),故母源性抗體可保護(hù)新生兒免受相應(yīng)病原體的感染。因此,孕期接種疫苗不僅能預(yù)防孕婦相應(yīng)的病原體感染,而且可以保護(hù)新生兒避免相應(yīng)病原體感染。理論上,孕期不能接種活疫苗,如麻疹疫苗、水痘疫苗,但是,可以接種滅活疫苗或類毒素。同時有研究顯示,孕期接種乙肝疫苗、破傷風(fēng)疫苗、白喉疫苗、滅活流感疫苗等是安全的[28,29]。Englund等[30]研究發(fā)現(xiàn),孕婦在不同孕周接種B型流感嗜血桿菌疫苗,抗體胎盤轉(zhuǎn)運(yùn)效率不同。在孕32周、36周時接種,分別有82%及92%的抗體轉(zhuǎn)運(yùn)至胎兒;另一研究中,孕婦分別在預(yù)產(chǎn)期前7~14天、14~28天、大于28天接種該疫苗,結(jié)果發(fā)現(xiàn)在出生前4周接種,新生兒抗體滴度最高。在英國和美國,推薦孕期接種流行性感冒疫苗和百日咳疫苗。研究顯示,孕期接種破傷風(fēng)、百日咳、流感疫苗可有效保護(hù)新生兒免受相應(yīng)病原體的感染[31]。多數(shù)研究顯示,高濃度的母源性呼吸道合胞病毒可以保護(hù)新生兒免受該病毒感染,但少部分研究顯示,高濃度的母源性呼吸道合胞病毒不但沒有臨床益處,反而增加反復(fù)哮喘的風(fēng)險[32]。有研究顯示孕期按照0、1、4個月方案接種乙肝疫苗的保護(hù)性抗體陽性率可達(dá)90%[33]。然而,孕期接種時機(jī)對母胎抗體轉(zhuǎn)運(yùn)有一定影響。Healy等[34]對105例孕前或孕期注射百日咳加強(qiáng)疫苗的孕婦研究發(fā)現(xiàn),在孕前和孕早期加強(qiáng)注射百日咳疫苗,新生兒不能獲得足夠的母源性百日咳抗體以保護(hù)其不受感染。
自1949年Vahlquist等發(fā)現(xiàn)母源性抗體對新生兒接種白喉類毒素后的免疫應(yīng)答有影響起,大量研究顯示,母源性抗體能抑制機(jī)體對疫苗的免疫應(yīng)答,從而影響疫苗效果,包括百日咳、破傷風(fēng)、流行性腦脊髓膜炎、B型嗜血性流感桿菌、呼吸道合胞病毒肺炎、流感病毒、狂犬病毒、甲型肝炎病毒、肺炎球菌等疫苗,但影響程度因病原種類和疫苗類型不同而存在差異。
高滴度的母源性抗體比低滴度時明顯抑制嬰兒的抗體應(yīng)答,表現(xiàn)為血清陽轉(zhuǎn)率和(或)幾何平均滴度降低。Jones等[35]研究顯示,在母源性抗體存在的情況下,嬰兒接種破傷風(fēng)疫苗、肺炎球菌疫苗、百日咳疫苗和B型流感嗜血桿菌疫苗后4周,除破傷風(fēng)抗體與出生時無明顯差異,其他抗體濃度均明顯高于出生時,分別有97%的嬰兒存在保護(hù)性B型流感嗜血桿菌抗體,89%的存在保護(hù)性百日咳抗體、100%的存在保護(hù)性破傷風(fēng)抗體。但是接種疫苗后4周的破傷風(fēng)抗體濃度、肺炎球菌抗體濃度、百日咳抗體濃度和B型流感嗜血桿菌抗體濃度均與相應(yīng)的母源性抗體濃度呈負(fù)相關(guān),分別為-0.86、-0.82、-0.77、-0.66,母源性破傷風(fēng)抗體及肺炎球菌抗體濃度最高的嬰兒接種相應(yīng)疫苗后免疫應(yīng)答最低。母源性輪狀病毒抗體可抑制嬰兒對ORV-115E疫苗的應(yīng)答,但是加大接種疫苗的劑量可克服該抑制作用[36]。母源性甲肝抗體的臨界值為300~400 mIU/ml時,注射甲肝疫苗即可誘導(dǎo)嬰兒體液免疫應(yīng)答[37]。只有當(dāng)母源性抗體降至某個臨界值以下時,新生兒才能對初次疫苗接種產(chǎn)生抗體應(yīng)答,該臨界值只有通過實(shí)驗(yàn)研究才能確定。
目前,雖然有研究顯示某些新的DNA疫苗或新的疫苗組分可消除母源性抗體對免疫接種的影響,但是最廣泛使用的方法是推遲疫苗接種時間,待嬰兒體內(nèi)的母源性體抗體自然衰退到某臨界值以下,以克服母源性抗體對嬰兒預(yù)防接種的影響。目前,B型嗜血流感桿菌預(yù)防接種時間在2月齡以上,脊髓灰質(zhì)炎疫苗于2月齡口服,百白破三聯(lián)疫苗于3月齡以后注射,麻疹疫苗在發(fā)展中國家一般在6~9月齡接種,甲肝疫苗接種一般推遲至1~2歲。對216例英國母親及其嬰兒的研究顯示,孕婦及其嬰兒2月齡時的脊髓灰質(zhì)炎抗體濃度均較低,嬰兒在2月齡和4月齡分別接種脊髓灰質(zhì)炎疫苗可使90%嬰兒獲得保護(hù)性抗體[38]。只有卡介苗(通過細(xì)胞免疫起作用)和乙肝疫苗在出生時接種。我們的研究顯示,高濃度母源性抗-HBs,可抑制乙肝疫苗前2針接種效果[39],但不影響新生兒接種乙型肝炎疫苗后遠(yuǎn)期效果[40]。
母源性抗體水平的變化有可能引起人群的免疫水平改變,從而引起某些疾病的流行規(guī)律的變化[41,42]。隨著免疫接種的廣泛推行,自然感染人群逐漸變少,而免疫接種產(chǎn)生的抗體較自然感染獲得的抗體濃度低[12],一些嬰兒在免疫接種時母源性抗體已降低至保護(hù)水平的閾值以下,從而在疫苗接種前出現(xiàn)流行。近年嬰幼兒麻疹發(fā)病率有升高趨勢[43],Garnier等[44]研究了母源性抗體對麻疹流行的影響。國內(nèi)也有報道顯示,母親接種獲得麻疹抗體較自然感染者偏低,其新生兒可在免疫接種前即感染[45]。
總之,母源性抗體在保護(hù)新生兒及嬰幼兒免受相應(yīng)病原體感染的同時,也可影響機(jī)體對相應(yīng)疫苗的免疫應(yīng)答。隨著人群抗體水平的不斷變化,需要新疫苗的研制或是不斷調(diào)整免疫方案,使得人類免受相關(guān)病原體的感染。
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R186
A
2014-12-29)
編輯:劉鄧浩
10.13470/j.cnki.cjpd.2015.01.013