牙齦卟啉單胞菌在牙周炎病理和防治中的研究進展*

黃鏡靜,武 曦 綜述,譚穎徽審校

(第三軍醫(yī)大學新橋醫(yī)院口腔科,重慶 400037)

牙齦卟啉單胞菌在牙周炎病理和防治中的研究進展*

黃鏡靜,武 曦 綜述,譚穎徽△審校

(第三軍醫(yī)大學新橋醫(yī)院口腔科,重慶 400037)

卟啉單胞菌,牙髓;牙周炎;病理過程;牙疾病預防

牙周炎是細菌及其產(chǎn)物引起的慢性感染性疾病,并引起宿主的免疫應答和炎性反應,造成牙周組織的直接和間接破壞?牙齦卟啉單胞菌(porphyromonas gingivalis,Pg)是牙周病變區(qū)最主要的優(yōu)勢菌,在慢性牙周炎?侵襲性牙周炎?牙周膿腫等的發(fā)生?發(fā)展中起重要作用,是牙周微生態(tài)學的研究熱點,在微生物學?分子生物學?基因工程等方面都取得了一定進展?

1 基本特性

Pg是革蘭陰性無芽孢有菌毛的專性厭氧桿菌,細菌自身不發(fā)酵葡萄糖,能產(chǎn)生蛋白酶為其提供能量,在血平板上培養(yǎng)能代謝鐵儲存亞鐵血紅素形成特征性的黑色菌落[1],CDC厭氧血瓊脂培養(yǎng)基中加入的氯化血紅素?維生素K1和綿羊凍血能促進細菌生長和黑色素形成[2]?

2 分 布

Pg在健康人齦溝?唾液?齦上菌斑?口腔黏膜等部位較少,但在齦下菌斑尤其病變的牙周組織中數(shù)量顯著增多?研究表明,牙周健康者檢出的Pg主要是fimAⅠ型Pg,而慢性牙周炎患者主要與fimAⅡ型和fimAⅣ型Pg有關(guān)[3]?齦下菌斑是牙周炎的進展前沿,與牙周組織的快速破壞相關(guān),Pg通過與其他細菌和宿主的相互作用影響了齦下菌斑的形成和構(gòu)成,改變了牙菌斑生態(tài)系,從而導致牙周疾病的發(fā)生?發(fā)展?

3 致病物質(zhì)及機制

Pg有關(guān)的致病物質(zhì)主要分兩類,(1)菌體成分:菌毛?纖毛?外膜?莢膜;(2)菌體產(chǎn)生的毒力因子:內(nèi)毒素?蛋白酶以及一些代謝產(chǎn)物等?

3.1 Pg介導的病原體黏附和聚集 牙菌斑是牙周炎的始動因子,細菌的聚集和黏附是致病的先決條件?口腔細菌的相互作用主要有以下3種:(1)通過凝集素-糖類樣機制介導自身的共聚和其他細菌的凝集,研究表明Pg能通過自身的菌毛蛋白與福賽擬桿菌(bacteroides forsythus,Bf)?伴放線桿菌(actinobacillus actinomycetem comitans,Aa)的菌體多糖特異性結(jié)合,這種結(jié)合受單糖和氨基酸的調(diào)節(jié),但不受溫度影響;(2)蛋白質(zhì)和蛋白質(zhì)間的相互作用,主要是與唾液獲得性膜間的相互作用,易受溫度影響;(3)氫鍵?疏水鍵?親水鍵等的輔助作用,Pg的表面結(jié)構(gòu)如疏水性強的纖毛?莢膜?外膜等與其相關(guān)[4-5]?3.2 Pg對宿主組織的侵入 與正常組織相比,牙周病變部位侵入的細菌數(shù)量顯著增多,Jandik等[6]通過菌落形成單位的測定顯示Pg在病變位點有更強的侵襲能力?Pg的侵襲能力還受其他細菌的影響,Saito等[7]研究發(fā)現(xiàn)具核梭桿菌(fusobacterium nucleatum,Fn)可以顯著增強Pg的入侵,Aa和Bf卻減弱Pg的入侵,這表明不同種類的病原體在入侵過程中存在協(xié)同和拮抗作用?菌毛可以介導病原體穿越上皮屏障,Amano[8]研究發(fā)現(xiàn)在菌毛的6種基因型(Ⅰ～Ⅴ?Ⅰb型)中,具有Ⅱ型菌毛的Pg可以通過降解整合素相關(guān)的信號分子,破壞上皮屏障和上皮細胞功能從而侵入宿主組織?

3.3 Pg介導的免疫逃逸和組織損傷 Pg能逃避和抵抗宿主的防御反應,這是其得以在宿主體內(nèi)適應性定植和生長的關(guān)鍵因素?Wang等[9]發(fā)現(xiàn)Pg菌毛蛋白的部分成分FimCDE能增強病原體適應性,介導病原體逃避細胞內(nèi)殺傷機制;與其他病原體相比,Pg細胞壁成分肽聚糖的片段,在刺激結(jié)合齦溝上皮受體方面具有弱的免疫活性,此外,Pg的脂多糖(lipopolysaccharide,LPS)具有特殊的結(jié)構(gòu)脂質(zhì)A,可以作為TLR4的拮抗劑,抑制了炎癥的NF-kappaB通路[10],并且隨炎癥部位溫度的變化,脂質(zhì)A可以變構(gòu)調(diào)節(jié)宿主的免疫應答[11];Brunner等[12]首次發(fā)現(xiàn)Pg的莢膜多糖可以通過減少白細胞介素(IL-1β?IL-6?IL-8)等來抑制宿主的免疫應答,這些可能是其逃脫免疫系統(tǒng)的內(nèi)源分子機制,從而誘發(fā)牙周組織炎癥?

Pg侵入機體組織后,能通過各種途徑介導牙周組織的損傷?其LPS對成纖維細胞有明顯的細胞毒作用,可抑制人牙齦成纖維細胞的生長和增殖,降低成纖維細胞附著和定向移動能力,還可以抑制牙周膜細胞的活性和分化[13],并能與一些炎癥介質(zhì)如IFN-γ協(xié)同作用,增加局部組織氧自由基產(chǎn)生,促進成纖維細胞凋亡[14]?LPS能通過激活Notch1信號抑制成骨細胞前體細胞的成骨分化[15],并抑制成骨細胞的生長?分化和功能,抑制骨形成,改變病變部位牙槽骨改建的動態(tài)平衡[16-17]?LPS還能刺激肥大細胞脫顆粒產(chǎn)生前炎癥介質(zhì)如白三烯,增加微血管通透性造成局部水腫,并使肥大細胞表面的TLR2和TLR4表達增高[18]?內(nèi)毒素(endotoxin)是革蘭陰性菌細胞壁外膜的LPS成分,可在細菌死亡或裂解時釋放,也可由活菌以細胞壁發(fā)泡的形式釋放?

Pg能產(chǎn)生許多細胞外蛋白酶,如牙齦素(gingipains,gps)?膠原酶,是破壞宿主組織的重要毒力因子,能降解非常廣泛的底物,直接參與牙周組織的破壞和降解?牙齦素是存在于Pg外膜?膜泡?胞外的一組蛋白酶,為半胱氨酸酶類,包括精氨酸-牙齦素(arginine-gingipains,Rgps?RgpA和RgpB)和賴氨酸-牙齦素(lysine-gingipain,Kgp)?Pg產(chǎn)生的牙齦素(1)能破壞上皮屏障的功能,使細菌滲透入牙周結(jié)締組織中[19];(2)能滅活中性粒細胞產(chǎn)生的抗微生物多肽LL-37,使其喪失與LPS結(jié)合的能力和殺菌活性[20];(3)能裂解表達于口腔上皮的ICAM-1,干擾了中性粒細胞的黏附和免疫作用[21];(4)能降解炎癥介質(zhì)如IL-4?IL-5等[22]或其配體如 TNF-α的配體CD27[23],使機體免疫功能紊亂,有利于細菌在齦下菌斑的生長繁殖和疾病的發(fā)生;(5)能輔助細菌逃脫機體血清抗體的免疫應答[24]?

4 Pg在牙周炎防治中的研究現(xiàn)狀和展望

Pg是牙周炎的主要致病菌,毒力較強,因此國內(nèi)外學者針對Pg的牙周病防治進行了大量研究,已經(jīng)深入到分子水平并取得了一定進展?

通過篩選針對牙周致病菌的敏感藥物或天然物質(zhì),制成牙周緩釋劑,其抑菌作用可輔助治療和控制牙周感染[25-26]?一些研究針對FimAⅠ?Ⅱ?Ⅳ型Pg菌毛制備的單克隆抗體能有效中和Pg所致的感染,其中抗FimAⅡ型Pg的單克隆抗體可以抑制人牙齦成纖維細胞中IL-8的產(chǎn)生[27-28]?

將Pg外膜蛋白抗體制成的疫苗經(jīng)皮免疫通過抑制Pg的共聚,可以阻止Pg的感染,從而有效阻止慢性牙周炎的進展[29-31];Yu等[32]針 對 Pg 的 FimA 構(gòu) 建 了 靶 向 質(zhì) 粒 DNA 疫苗,能有效預防實驗動物的牙槽骨喪失;Pg菌毛蛋白免疫動物能阻止牙槽骨吸收?

牙周炎疫苗的研究剛剛起步,有關(guān)全菌免疫還存在一定爭議,菌體成分復雜,而且全細胞抗原多,增加了與人體組織免疫交叉反應的危險性,在牙周炎病原菌的眾多抗原分子中,選擇有效且具有免疫保護作用的抗原分子,是研究的熱點問題?此外不同病原菌的抗原分子,其單獨或共同作用時,對機體的免疫系統(tǒng)的影響都有待于進一步研究?

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10.3969/j.issn.1671-8348.2012.18.034

A

1671-8348(2012)18-1869-03

* 基金項目:軍隊醫(yī)藥衛(wèi)生科研基金項目課題(06MA184)?△

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