王穎 蘇娟
【摘 要】 近年來(lái),國(guó)內(nèi)外學(xué)者對(duì)維生素D的研究不斷深入,發(fā)現(xiàn)其不僅參與鈣、磷代謝,而且在免疫調(diào)節(jié)方面也發(fā)揮重要作用。鑒于維生素D在免疫調(diào)節(jié)中的作用,其在某些自身免疫性疾病如類風(fēng)濕關(guān)節(jié)炎、系統(tǒng)性紅斑狼瘡、干燥綜合征、貝赫切特病等疾病中的作用逐漸被發(fā)現(xiàn)。就維生素D在免疫調(diào)節(jié)方面的作用及其在自身免疫性疾病中的研究進(jìn)展作一概述。
【關(guān)鍵詞】 維生素D;維生素D受體;自身免疫性疾病;綜述
維生素D為脂溶性維生素,是固醇類衍生物,亦是機(jī)體必須營(yíng)養(yǎng)素之一。1,25-(OH)2D3是其主要活性形式,機(jī)體主要通過(guò)自身合成及從食物中攝取獲得。
高等動(dòng)物皮膚中7-脫氫膽固醇經(jīng)光化學(xué)反應(yīng)轉(zhuǎn)化為維生素D3,而植物的麥角固醇經(jīng)日光照射后轉(zhuǎn)化為維生素D2。食物維生素D3/D2經(jīng)膽汁、小腸乳化作用吸收入血,由血漿α-球蛋白轉(zhuǎn)運(yùn)至肝細(xì)胞內(nèi)質(zhì)網(wǎng)及線粒體內(nèi)并在25-羥化酶作用下轉(zhuǎn)化為25-(OH)D3。后者經(jīng)血液循環(huán)到達(dá)腎近端小管上皮細(xì)胞線粒體內(nèi),并在1-α羥化酶作用下轉(zhuǎn)化為1,25-(OH)2D3,見(jiàn)圖1。
維生素D受體(Vitamin D receptor,VDR)為親核受體,分為細(xì)胞膜受體(mVDR)和細(xì)胞核受體(nVDR)兩類。前者主要維持鈣磷代謝平衡,后者主要通過(guò)調(diào)節(jié)基因表達(dá)調(diào)控相應(yīng)蛋白質(zhì)合成,發(fā)揮免疫調(diào)節(jié)等作用。絕大多數(shù)免疫細(xì)胞如單核/巨噬細(xì)胞,樹(shù)突狀細(xì)胞,中性粒細(xì)胞,活化T、B細(xì)胞等均表達(dá)VDR。維生素D通過(guò)與VDR結(jié)合發(fā)揮調(diào)節(jié)鈣磷代謝、免疫調(diào)節(jié)等作用,見(jiàn)圖1。
1 維生素D的免疫調(diào)節(jié)作用
1.1 維生素D與單核/巨噬細(xì)胞 維生素D可促進(jìn)單核細(xì)胞分化為巨噬細(xì)胞,增強(qiáng)后者趨化、吞噬能力,誘導(dǎo)單核/巨噬細(xì)胞對(duì)微生物殺傷功能;抑制單核細(xì)胞向樹(shù)突狀細(xì)胞分化,間接抑制后者表面MHC-Ⅱ表達(dá),抑制抗原提呈及初始T細(xì)胞活化。且為避免機(jī)體處于炎癥后期單核細(xì)胞表面TLR過(guò)度活化及嚴(yán)重炎性反應(yīng),維生素D可減少單核細(xì)胞表面TLR2、TLR4表達(dá),使機(jī)體對(duì)病原相關(guān)模式分子反應(yīng)處于較低狀態(tài)[1]。此外,維生素D還能誘導(dǎo)大鼠骨髓來(lái)源單核細(xì)胞形成破骨細(xì)胞[2]。維生素D不僅能增強(qiáng)單核/巨噬細(xì)胞趨化、吞噬、殺傷等功能,還可調(diào)節(jié)機(jī)體過(guò)度激活的免疫系統(tǒng),此外還可誘導(dǎo)單核細(xì)胞分化為破骨細(xì)胞參與骨代謝過(guò)程。
1.2 維生素D與樹(shù)突狀細(xì)胞(dendritic cell,DC)
成熟DC可活化初始T淋巴細(xì)胞,啟動(dòng)適應(yīng)性免疫應(yīng)答。維生素D能阻止幼稚DC向成熟DC分化,導(dǎo)致其下調(diào)MHC-Ⅱ分子、共刺激分子CD40、CD86及CD83表達(dá)[3],使DC分泌Th1極化細(xì)胞因子白細(xì)胞介素-12(IL-12)及Th17極化細(xì)胞因子IL-23減少,分泌Treg細(xì)胞刺激因子IL-10增多,減少DC依賴性T細(xì)胞活化,誘導(dǎo)具有免疫耐受表型DC。維生素D可能通過(guò)調(diào)節(jié)DC分化及分泌細(xì)胞因子分子水平在誘導(dǎo)機(jī)體免疫耐受中發(fā)揮重要作用。
1.3 維生素D與中性粒細(xì)胞 維生素D可增強(qiáng)中性粒細(xì)胞的抗菌肽活性,以增強(qiáng)機(jī)體抵御病原體能力。可見(jiàn)維生素D在增強(qiáng)中性粒細(xì)胞抗菌能力、促進(jìn)后者發(fā)揮殺菌等免疫防御功能中起重要作用。
1.4 維生素D與T淋巴細(xì)胞 維生素D抑制Th1型細(xì)胞增殖,使其分泌IL-2、IFN-γ減少。維生素D還能通過(guò)增加Th2型細(xì)胞特異性轉(zhuǎn)錄因子GATA-3及cmaf表達(dá),促進(jìn)Th2型細(xì)胞因子IL-4、IL-6、IL-10分泌[4],增強(qiáng)Th2型免疫反應(yīng),使Th1型免疫反應(yīng)向Th2型偏移。此外,維生素D還可抑制Th17細(xì)胞分泌IL-17等促炎因子,抑制Th17細(xì)胞免疫反應(yīng)[5]??梢?jiàn)維生素D可通過(guò)調(diào)節(jié)T細(xì)胞不同亞群增殖、分泌影響免疫反應(yīng)類型。
1.5 維生素D與B淋巴細(xì)胞 維生素D可抑制B淋巴細(xì)胞增殖、誘導(dǎo)其凋亡,進(jìn)而抑制漿細(xì)胞生成,減少免疫球蛋白產(chǎn)生[6]。
2 維生素D在自身免疫性疾?。╝utoimmune disease,AID)中的作用
2.1 維生素D與類風(fēng)濕關(guān)節(jié)炎(rheumatoid arthritis,
RA) RA是一種以滑膜炎為特征的AID免疫性疾病。RA患者血清中維生素D水平及外周血淋巴細(xì)胞VDR mRVA表達(dá)減少,且維生素D水平與DAS28、紅細(xì)胞沉降率、C-反應(yīng)蛋白等疾病活動(dòng)指標(biāo)呈負(fù)相關(guān)[7-8],增加維生素D攝入可延緩和預(yù)防RA發(fā)生發(fā)展。Gardner等[9]研究發(fā)現(xiàn),1,25-(OH)2D3可通過(guò)抑制RA患者CD4+T淋巴細(xì)胞表面TCR以增強(qiáng)阿貝西普對(duì)CD4+T細(xì)胞活化的抑制作用。Feng等[10]發(fā)現(xiàn),1,25-(OH)2D3
可顯著增加RA患者滑膜成纖維細(xì)胞MH7A中由IL-1β誘導(dǎo)的OPG/RANKL比率,減低細(xì)胞中由IL-1β誘導(dǎo)的IL-6及腫瘤壞死因子-α(TNF-α)mRNA水平及滑膜液中IL-6表達(dá),在滑膜組織炎性環(huán)境下發(fā)揮抗炎作用,抑制炎癥誘導(dǎo)的破骨細(xì)胞形成。另有研究發(fā)現(xiàn),1,25-(OH)2D3還可通過(guò)抑制RA患者細(xì)胞核轉(zhuǎn)錄因子-κB受體活化因子配體(RANKL)產(chǎn)生,抑制外周血單核細(xì)胞分泌與RANKL通路相關(guān)細(xì)胞因子TNF-α、IL-6、IL-17等,抑制骨侵蝕與破壞[11]。此外,補(bǔ)充維生素D對(duì)RA微血管功能改善亦有一定益處[12]。由此推測(cè),維生素D/VDR通路在RA中可能通過(guò)抑制CD4+T活化以及減少炎性因子介導(dǎo)的骨破壞發(fā)揮重要作用。
2.2 維生素D與系統(tǒng)性紅斑狼瘡(systemic lupus erythematosus,SLE) SLE存在細(xì)胞凋亡率增加,對(duì)凋亡細(xì)胞清除障礙,未被清除的凋亡物質(zhì)獲得免疫原性,攻擊免疫系統(tǒng),破壞自身抗原耐受機(jī)制可能導(dǎo)致該病。Tabasi等[13]發(fā)現(xiàn),維生素D可通過(guò)上調(diào)Bcl-2,下調(diào)Bax、FasL基因表達(dá)抑制SLE患者外周血單核細(xì)胞凋亡,減少單核細(xì)胞凋亡率。SLE患者普遍存在維生素D缺乏,且其水平與疾病活動(dòng)度呈負(fù)相關(guān)[14],補(bǔ)充維生素D可緩解病情。SLE誘導(dǎo)免疫耐受的調(diào)節(jié)性T細(xì)胞減少及輔助性T細(xì)胞增多。Terrier等[15]發(fā)現(xiàn),補(bǔ)充維生素D可增加SLE患者調(diào)節(jié)性T細(xì)胞,減少Th1、Th17細(xì)胞水平,使抗ds-DNA抗體水平減低,推測(cè)維生素D可能通過(guò)抑制B細(xì)胞功能進(jìn)而影響抗體產(chǎn)生。此外,SLE患者亦存在血管內(nèi)皮損傷及內(nèi)皮功能障礙。國(guó)外研究發(fā)現(xiàn),補(bǔ)充維生素D可減少SLE患者因中性粒細(xì)胞胞外誘捕網(wǎng)形成引起的血管內(nèi)皮損傷,還可下調(diào)CXCL-10表達(dá)以增強(qiáng)骨髓血管形成細(xì)胞(MAC)血管形成能力,以改善SLE患者血管內(nèi)皮細(xì)胞功能[16-17]。維生素D在SLE中可能發(fā)揮抑制單核細(xì)胞凋亡、抑制B細(xì)胞功能、減少自身抗體生成,及改善內(nèi)皮細(xì)胞功能等作用,為SLE治療提供了新思路。
2.3 維生素D與原發(fā)性干燥綜合征(primary Sj?gren's syndrome,pSS) pSS女性患者維生素D缺乏較為明顯,維生素D缺乏是其危險(xiǎn)因素之一[18]。Yoon等[19]發(fā)現(xiàn),血清中維生素D減低與干眼癥相關(guān)。另有研究表明,維生素D缺乏的pSS患者易并發(fā)遠(yuǎn)端腎小管酸中毒、低鉀血癥等疾病[20]。目前維生素D在pSS發(fā)病中如何發(fā)揮作用尚無(wú)相關(guān)報(bào)道,還有待進(jìn)一步探究。補(bǔ)充維生素D可能為pSS治療提供一定幫助。
2.4 維生素D與貝赫切特?。˙ehcet's disease,
BD) BD發(fā)病進(jìn)程中存在Th1、Th2免疫平衡失調(diào),其中以Th1型免疫反應(yīng)占優(yōu)勢(shì),此外Th17細(xì)胞也參與了其發(fā)病。BD患者普遍存在維生素D缺乏[21],研究表明,維生素D可通過(guò)DC抑制BD患者Th17、Th1型免疫反應(yīng)[22]。此外,研究發(fā)現(xiàn),BD患者疾病活動(dòng)期單核細(xì)胞表面TLR2、TLR4表達(dá)水平升高[23],且BD患者血清中維生素D水平與單核細(xì)胞表面TLR2、TLR4水平呈負(fù)相關(guān),且維生素D缺乏的BD患者補(bǔ)充維生素D后其單核細(xì)胞表面TLR2、TLR4水平減低進(jìn)而抑制促炎因子TNF-α合成,減緩病情。但Güng?r等[24]發(fā)現(xiàn),BD患者血清中25(OH)D水平與患者內(nèi)皮細(xì)胞功能障礙情況呈負(fù)相關(guān),且補(bǔ)充維生素D后其內(nèi)皮細(xì)胞功能改善,但單核細(xì)胞表面TLR2、TLR3水平于補(bǔ)充維生素D前后無(wú)差異。維生素D可能通過(guò)削弱Th1型免疫反應(yīng)及Th17細(xì)胞功能以及改善血管內(nèi)皮細(xì)胞功能在BD中發(fā)揮重要作用。但其對(duì)BD患者單核細(xì)胞TLR水平的影響仍存在爭(zhēng)議,有待進(jìn)一步探究。補(bǔ)充維生素D可能為BD治療提供新方向。
2.5 維生素D與銀屑病 銀屑病是一種以表皮角化過(guò)度伴角化不全,真皮乳頭毛細(xì)血管增生、擴(kuò)張為特征的疾病。該病存在Th1/Th2細(xì)胞亞群分化失調(diào)[25],且經(jīng)免疫偏移法將Th1細(xì)胞誘導(dǎo)偏移為T(mén)h2細(xì)胞可有效改善銀屑病癥狀。維生素D具有調(diào)節(jié)表皮細(xì)胞向終末期分化,抑制角化細(xì)胞增殖作用,且可促進(jìn)Th2細(xì)胞的偏移,目前已應(yīng)用于臨床治療銀屑病,在改善皮損及關(guān)節(jié)癥狀方面取得了一定療效。
2.6 維生素D與炎性腸病 炎性腸病包括潰瘍性結(jié)腸炎、克羅恩病,其病因及發(fā)病機(jī)制較復(fù)雜,主要涉及免疫、遺傳及環(huán)境等方面。其中,機(jī)體腸黏膜免疫系統(tǒng)功能異常在其發(fā)病中起重要作用。Hassan等[26]發(fā)現(xiàn),95%炎性腸病患者存在維生素D缺乏。Meckel等[27]研究發(fā)現(xiàn),潰瘍性結(jié)腸炎患者存在維生素D缺乏,且維生素D水平與患者腸黏膜炎中炎性因子TNF-α、IL-8、疾病活動(dòng)程度呈負(fù)相關(guān),與腸黏膜中VDR水平呈正相關(guān)。維生素D可能通過(guò)影響細(xì)胞因子TNF-α、IL-8等水平在炎性腸病局部黏膜免疫中發(fā)揮重要作用,但具體機(jī)制尚未闡明,有待進(jìn)一步探究。
2.7 維生素D與原發(fā)性膽汁性肝硬化(primary biliary cirrhosis,PBC) PBC患者血清中維生素D水平降低,其水平與血清堿性磷酸酶水平呈負(fù)相關(guān),且治療前血清中維生素D水平與患者對(duì)該病的治療藥物熊去氧膽酸療效相關(guān)[28-29]。維生素D可通過(guò)抑制基質(zhì)金屬蛋白酶、前列腺素、活性氧、轉(zhuǎn)化生長(zhǎng)因子-β等表達(dá)在PBC中發(fā)揮作用[30]。維生素D可能通過(guò)影響上述物質(zhì)水平影響該病進(jìn)程。維生素D可作為PBC預(yù)后評(píng)估、用藥前藥物療效預(yù)測(cè)指標(biāo),且補(bǔ)充維生素D可能為該病治療提供幫助。
2.8 維生素D與多發(fā)性硬化(multiple sclerosis,MS)
MS是一種慢性炎癥性脫髓鞘性疾病。Th1、Th17細(xì)胞增殖可提高M(jìn)S發(fā)病率、復(fù)發(fā)率,而Th2細(xì)胞增殖及其分泌的細(xì)胞因子可減緩其進(jìn)展。日照時(shí)間長(zhǎng)短和維生素D攝入量與MS發(fā)病率呈負(fù)相關(guān)[31]。Gargari等[32]發(fā)現(xiàn),補(bǔ)充維生素D可使MS患者外周血單核細(xì)胞表達(dá)IL-6、IL-17A基因下調(diào),減緩疾病進(jìn)展。此外,Gu等[33]通過(guò)對(duì)MS鼠模型相關(guān)研究發(fā)現(xiàn),補(bǔ)充維生素D可以減少凋亡引起的損傷,觸發(fā)神經(jīng)干細(xì)胞生長(zhǎng),改善MS模型鼠的中樞神經(jīng)系統(tǒng)病理變化。由此推斷,維生素D可能在調(diào)節(jié)MS患者Th2細(xì)胞增殖、分泌以及抗神經(jīng)細(xì)胞凋亡中發(fā)揮重要作用??梢?jiàn)維生素D作為新型免疫調(diào)節(jié)劑可能為MS預(yù)防及治療提供新思路。
2.9 維生素D與自身免疫性甲狀腺炎 Bozkurt等[34]研究發(fā)現(xiàn),橋本氏甲狀腺炎患者血清中25-(OH)D3水平減低,且與抗甲狀腺過(guò)氧化物酶抗體水平呈負(fù)相關(guān)。補(bǔ)充維生素D可以減少自身免疫性甲狀腺炎患者抗甲狀腺過(guò)氧化物酶抗體的產(chǎn)生[35]。
?iklar等[36]研究發(fā)現(xiàn),維生素D可能通過(guò)調(diào)節(jié)Treg細(xì)胞功能參與該病進(jìn)程。維生素D可能通過(guò)調(diào)節(jié)Treg細(xì)胞功能、抑制漿細(xì)胞產(chǎn)生抗體在該病中發(fā)揮作用,這為該病治療提供新方向,但具體機(jī)制仍待進(jìn)一步闡明。
3 展 望
綜上所述,維生素D在免疫調(diào)節(jié)方面作用主要表現(xiàn)為促進(jìn)機(jī)體固有免疫細(xì)胞功能,抑制適應(yīng)性免疫細(xì)胞功能。并在多種AID中發(fā)揮諸多重要作用,如調(diào)節(jié)Th1/Th2型免疫反應(yīng),調(diào)節(jié)Th17細(xì)胞、DC、B細(xì)胞、漿細(xì)胞等細(xì)胞功能的作用。且其VDR基因多態(tài)性與多種AID如RA、SLE、MS、BD等相關(guān)[37-42]。深入研究維生素D/VDR通路在上述疾病中的作用,將為研究疾病發(fā)病機(jī)制乃至治療提供更多理論依據(jù)。鑒于維生素D在此類疾病中的作用,維生素D作為新型的免疫調(diào)節(jié)劑為多種AID預(yù)防和治療提供廣闊思路,但其具體作用與機(jī)制有待進(jìn)一步探究。
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收稿日期:2016-09-23;修回日期:2016-11-16