王敬 雍康 吳有華 楊慶穩(wěn)
摘要:乳腺內(nèi)細(xì)菌感染可引起奶牛慢性型、臨床型和亞臨床型乳房炎。不同臨床結(jié)果的出現(xiàn),主要與細(xì)菌感染后激活乳腺免疫系統(tǒng)的方式不同有關(guān)。清晰地認(rèn)識乳腺免疫系統(tǒng)激活和調(diào)節(jié)機制,對制定有效防治方案很有必要。綜述了大腸桿菌性乳房炎和金黃色葡萄球菌性乳房炎的乳腺防御機制,并對二者的免疫反應(yīng)進行了比較,旨在為奶牛乳房炎的臨床防治提供參考依據(jù)。
關(guān)鍵詞:奶牛;乳房炎;乳腺;細(xì)菌感染;免疫反應(yīng)
中圖分類號:S858.23;S857.26 文獻標(biāo)識碼:A文章編號:0439-8114(2014)09-1989-04
Advances on Defensive Mechanisms of Dairy Cow Mammary Gland Infection
WANG Jing,YONG Kang,WU You-hua,YANG Qing-wen
(Department of Animal Science and Technology, Chongqing Three Gorges Vocational College, Chongqing 404155, China)
Abstract: Intramammary bacterial infections can be caused by bovine clinical type, chronic and subclinical mastitis. Different clinical results are mainly related with bacterial infection after activating the immune system in different ways of breast. It is necessary to well understand the activation and regulation mechanism of the breast immune system for developing effective prevention programs. This paper reviews breast defensive mechanisms of the Escherichia coli mastitis and Staphylococcus aureus mastitis and the immune response to the two bacteria.
Key words: cow; mastitis; mammary gland; bacterial infection; immune response
乳房炎是奶牛常見病和多發(fā)病,也是危害奶牛業(yè)最為嚴(yán)重的一種疾病。注射抗生素是國內(nèi)外控制該病的主要手段,但細(xì)菌耐藥性和藥物殘留等問題迫使人們尋找更加安全、有效的方法來防治乳房炎。通過營養(yǎng)調(diào)控、遺傳選育等各種策略提高對乳房炎的抗性,降低乳房炎的發(fā)生率被認(rèn)為是防治該病的長久之策,實現(xiàn)這一目標(biāo)就需要對乳腺的防御機制進行深入了解[1]。
大部分乳腺感染是細(xì)菌突破了乳頭管的生理屏障。細(xì)菌一旦進入乳池,就會大量生長繁殖,如果先天免疫反應(yīng)未能及時建立,細(xì)菌就會定居在乳腺組織[2]。在分娩和泌乳早期,乳腺免疫功能下降,并且體細(xì)胞數(shù)(Somatic cell count,SCC)會在感染之前降低,這些因素均增加了乳房炎發(fā)生的風(fēng)險。除了這些宿主因素外,細(xì)菌種類的不同也會影響乳腺的免疫反應(yīng),最終出現(xiàn)不同的臨床結(jié)果[3]。
1乳腺的免疫反應(yīng)機制
1.1病原識別和免疫反應(yīng)的啟動
一個快速而有效的先天免疫反應(yīng)是基于對潛在病原體的早期識別[4]。先天免疫系統(tǒng)是非特異性的,當(dāng)表面有特定的模式識別受體(Pattern recognition receptor,PRR)或在宿主細(xì)胞內(nèi)結(jié)合特定的細(xì)菌時先天免疫系統(tǒng)被啟動。當(dāng)致病或非致病性微生物復(fù)制或降解時,這些不同的病原體所共有的保守結(jié)構(gòu)就會釋放[5]。
PRR在牛奶中的白細(xì)胞和乳腺上皮細(xì)胞表達[6]。Toll樣受體(The toll-like receptor,TLR)群是哺乳動物中發(fā)現(xiàn)13種類型受體中最具特色的一種。TLRs的激活啟動各種免疫調(diào)節(jié)劑的轉(zhuǎn)錄,隨后核因子NF-kB遷移進入細(xì)胞核。另一個重要的病原受體CD14在乳腺嗜中性粒細(xì)胞和巨噬細(xì)胞中被發(fā)現(xiàn),它結(jié)合脂多糖(Lipopolysaccharide,LPS)-蛋白質(zhì)復(fù)合物并誘導(dǎo)腫瘤壞死因子TNF-α的合成和釋放[5]。
1.2乳腺的免疫應(yīng)答
病原體被識別后,血液中的白細(xì)胞高效轉(zhuǎn)移到乳腺組織來抑制細(xì)菌生長[2]。具體來說,細(xì)菌感染后,嗜中性粒細(xì)胞被大量招募,通過超氧離子、次氯酸鹽、過氧化氫和其他可溶性防御因素,如乳鐵蛋白和防御素,可吞噬和殺死入侵的微生物[7]。
TNF-α既是乳腺免疫應(yīng)答最早的起始中心,在急性大腸桿菌性乳房炎中,也是發(fā)熱、內(nèi)毒素休克發(fā)展的中心。白細(xì)胞介素IL-8、 受激活調(diào)節(jié)的正常T細(xì)胞表達和分泌因子(RANTES)等趨化因子是從血液中吸引白細(xì)胞的關(guān)鍵。補體、乳鐵蛋白和溶菌酶也為炎癥反應(yīng)提供了便利[2,5]。
2不同病原體引發(fā)乳腺的免疫反應(yīng)
雖然病原真菌能引起乳房炎,但最常見的是細(xì)菌。大腸桿菌(Escherichia coli)和金黃色葡萄球菌(Staphylococcus aureus)是引起乳房炎最常見的兩種細(xì)菌[5]。
2.1大腸桿菌感染引起的乳房炎
急性大腸桿菌性乳房炎的特點是SCC快速和大量增加[8]。細(xì)胞壁LPS是這種形式乳房炎的發(fā)病核心[9]。宿主細(xì)胞通過與乳腺上皮細(xì)胞TLR-4的相互作用識別LPS[10]。LPS以劑量依賴性誘導(dǎo)SCC快速強烈增加,多種細(xì)胞因子如TNF-α,抗菌防御蛋白(如乳鐵蛋白和溶菌酶)和脂質(zhì)介質(zhì)(如環(huán)氧合酶-2和5-脂氧合酶),也由該內(nèi)毒素誘導(dǎo)[11,12]。
2.2金黃色葡萄球菌感染引起的乳房炎
金黃色葡萄球菌性乳房炎往往引起SCC的增加且持續(xù)時間較長,感染后可導(dǎo)致慢性和亞臨床性乳房炎[8]。被感染的乳腺細(xì)胞中TNF-α mRNA增量表達[13]。
相反,革蘭氏陰性菌脂多糖是主要免疫刺激分子,脂蛋白、肽聚糖和脂磷壁酸(Lipoteichoicacid,LTA)已被確定為革蘭氏陽性菌細(xì)胞壁成分,它們均被TLR-2所識別[5]。Yang等[14]研究發(fā)現(xiàn),金黃色葡萄球菌沒有誘導(dǎo)乳腺上皮細(xì)胞的NF-kB級聯(lián),Bougarn等[15]研究證明參與NF-kB刺激的細(xì)胞因子被LTA激活。此外,乳腺上皮細(xì)胞TLR-2是由金黃色葡萄球菌[10]和LTA激活[6]。
在體外,LTA通過乳腺上皮細(xì)胞誘導(dǎo)TNF-α、IL-6和IL-8的表達[16],肽聚糖或其他革蘭氏陽性細(xì)菌致病成分額外的刺激作用沒有使這個表達增強。Rainard等[17]證實乳房內(nèi)灌注LTA與體內(nèi)感染金黃色葡萄球菌的免疫反應(yīng)相比,牛奶中趨化因子和IL-1β增加,但TNF-α增加不明顯。
2.3其他病原體引起的乳房炎
乳房鏈球菌(Streptococcus uberis)是引發(fā)乳房炎的常見病原菌,它誘導(dǎo)TNF-α、IL-1β和IL-8分泌進入乳汁[18]。有趣的是,一株從急性乳房炎中分離得到的金黃色葡萄球菌在體外誘導(dǎo)乳腺上皮細(xì)胞IL-8和IL-1β的表達量比慢性乳房炎中分離得到的菌株誘導(dǎo)分別高出2倍和4倍[19]。此外,支原體、銅綠假單胞菌(Pseudomonas aeruginosa)、黏質(zhì)沙雷氏菌(Serratia marcescens)和肺炎克雷伯菌(Klebsiella pneumoniae)對牛乳房炎癥反應(yīng)的影響也有報道[20]。
3不同病原菌引發(fā)乳腺免疫反應(yīng)的差異
3.1大腸桿菌和金黃色葡萄球菌引發(fā)乳腺免疫反應(yīng)的差異
大腸桿菌性乳房炎發(fā)病急、病情重,經(jīng)常導(dǎo)致奶牛死亡。相反,金黃色葡萄球菌性乳房炎往往呈慢性亞臨床型。與大腸桿菌性乳房炎相比,金黃色葡萄球菌性乳房炎在牛奶中補體因子5a水平較低,TNF-α、IL-1β和IL-8的濃度沒有增加,這些生物誘導(dǎo)不同的免疫反應(yīng)最終表現(xiàn)在臨床上的差異[8]。然而,在這些研究中,盡管感染量是一定的,金黃色葡萄球菌在乳房內(nèi)的生長速率比大腸桿菌低得多。細(xì)菌生長速率的差異也可以解釋為什么大腸桿菌感染比金黃色葡萄球菌感染乳腺中β-防御素、TLR-2和TLR-4產(chǎn)量多。即使使用多于大腸桿菌20倍劑量的金黃色葡萄球菌感染,結(jié)果依然如此[3]。
與大腸桿菌感染相比,葡萄球菌感染的細(xì)胞中IL-8水平更高[21]。在體外,大腸桿菌感染24 h后乳腺上皮細(xì)胞IL-1β、TNF-α和IL-8 mRNA比金黃色葡萄球菌表達量大[22]。然而,感染后3 h,金黃色葡萄球菌所誘導(dǎo)的這些細(xì)胞因子的表達量比大腸桿菌明顯,但這種差異在感染10 h后消失。相同濃度下,熱滅活的大腸桿菌和金黃色葡萄球菌刺激體外培養(yǎng)的乳腺上皮細(xì)胞,TNF-α、IL-1β、IL-6、IL-8、RANTES和C3的表達量比大腸桿菌刺激在體乳腺上皮細(xì)胞產(chǎn)生的多[10]。Strandberg等[6]用LTA誘導(dǎo)體外培養(yǎng)的乳腺上皮細(xì)胞時發(fā)現(xiàn),細(xì)胞因子的表達量比LPS誘導(dǎo)產(chǎn)生的少??偟膩碚f,這個標(biāo)準(zhǔn)是很重要的,可量化的參數(shù)如SCC被用于不同PAMPS乳腺免疫反應(yīng)的比較研究[5]。
Wellnitz等[5]發(fā)現(xiàn)0.2 μg的LPS和20 μg的LTA分別接種到泌乳奶牛乳腺后誘導(dǎo)大約相同的SCC的增加,雖然誘導(dǎo)的細(xì)胞因子有變化,乳腺在LPS刺激下,牛奶中TNF-α、乳酸脫氫酶的濃度、TNF-α和IL-1 mRNA的表達量增加而LTA刺激并沒有出現(xiàn)類似的變化,LPS也是牛奶中細(xì)胞IL-8和RANTES更強的誘導(dǎo)劑。對人類白細(xì)胞的研究還表明,LTA是TNF-α的一個較弱的誘導(dǎo)因子。綜上所述,大腸桿菌和金黃色葡萄球菌激活乳腺免疫反應(yīng)的重要差異影響了這些感染的臨床表現(xiàn)[23](表1)。
乳腺感染易受到SCC的影響,低計數(shù)會增加乳房炎的風(fēng)險和嚴(yán)重性[5]。Suriyasathaporn等[24]發(fā)現(xiàn),低濃度的SCC會增加奶?;紘?yán)重大腸桿菌性乳房炎的風(fēng)險,而高計數(shù),動物則更易發(fā)生金黃色葡萄球菌性乳房炎。在感染乳房內(nèi)SCC增加或降低的速度因病原菌而異:大腸桿菌可引起SCC快速、高劑量的增加,而金黃色葡萄球菌感染會使SCC在2~3 d內(nèi)逐漸增加。Djabri等[25]計算不同的細(xì)菌感染乳腺SCC的平均值發(fā)現(xiàn),大腸桿菌SCC的計數(shù)比金黃色葡萄球菌更高。
3.2其他細(xì)菌乳腺免疫反應(yīng)的差異
與大腸桿菌和金黃色葡萄球菌相比,有關(guān)其他病原體的乳腺免疫反應(yīng)的報道較少。Bannerman等[26]對比了導(dǎo)致奶牛臨床型乳房炎發(fā)生的革蘭陰性黏質(zhì)沙雷氏菌和革蘭陽性鏈球菌的乳腺反應(yīng)發(fā)現(xiàn),這兩種細(xì)菌誘導(dǎo)牛奶中TNF-α、IL-1β水平提高。在體外,與滅活的金黃色葡萄球菌誘導(dǎo)相比,熱滅活的鏈球菌沒有觸發(fā)乳腺上皮細(xì)胞類似的免疫反應(yīng),雖然這兩種細(xì)菌都屬于革蘭氏陽性菌且均含有LTA[16]。
4展望
奶牛乳腺細(xì)菌感染可導(dǎo)致不同類型乳房炎的發(fā)生。這些差異是以不同的細(xì)菌在乳腺活化先天免疫反應(yīng)為基礎(chǔ)的。被感染乳腺中,細(xì)胞因子和SCC最終決定乳房炎的嚴(yán)重程度和發(fā)展速度,這有助于解釋為什么大腸桿菌比金黃色葡萄球菌引起的乳房炎更急、更嚴(yán)重。目前對乳腺感染其他病原體,比如鏈球菌、支原體、真菌等所引發(fā)的防御機制研究還不深入,需要進一步探索。
參考文獻:
[1] 雍康.奶牛S100A12基因克隆、原核表達及表達產(chǎn)物抗菌活性分析[D].四川雅安:四川農(nóng)業(yè)大學(xué),2011.
[2] SCHUKKEN Y H, G?譈NTHER J, FITZPATRICK J, et al. Host-response patterns of intramammaryinfections in dairy cows[J]. Veterinary Immunology and Immunopathology, 2011, 144(3-4):270-289.
[3] PETZL W, ZERBE H, G?譈NTHER J,et al. Escherichia coli but not Staphylococcus aureus triggers an early increased expression of factors contributing to the innate immune defense in the udder of the cow[J]. Veterinary Research,2008,39(2):18.
[4] AKIRA S, UEMATSU S, TAKEUCHI O. Pathogen recognition and innate immunity[J]. Cell, 2006,124(4):783-801.
[5] WELLNITZ O, BRUCKMAIER R M. The innate immune response of the bovine mammary gland to bacterial infection[J]. The Veterinary Journal, 2012,192(2):148-152
[6] STRANDBERG Y,GRAY C,VUOCOLO T,et al. Lipopolysaccharide and lipoteichoic acid induce different innate immune responses in bovine mammary epithelial cells[J]. Cytokine,2005,
31(1):72–86.
[7] PAAPE M J, BANNERMAN D D, ZHAO X,et al. The bovine neutrophil: Structure and function in blood and milk[J]. Veterinary Research, 2003,34(5):597-627.
[8] BANNERMAN D D, PAAPE M J,LEE J W,et al. Escherichia coli and Staphylococcus aureus elicit differential innate immune responses following intramammary infection[J]. Clinical and Diagnostic Laboratory Immunology,2004,11(3):463-472.
[9] GONEN E, VALLON-EBERHARD A,ELAZAR S,et al. Toll-like receptor 4 is needed to restrict the invasion of Escherichia coli P4 into mammary gland epithelial cells in a murine model of acute mastitis[J]. Cellular Microbiology, 2007,9(12):2826-2838.
[10] GRIESBECK-ZILCH B, MEYER H H D, K?譈HN C H, et al. Staphylococcus aureus and Escherichia coli cause deviating expression profiles of cytokines and lactoferrin messenger ribonucleic acid in mammary epithelial cells[J]. Journal of Dairy Science,2008,91(6):2215-2224.
[11] WELLNITZ O,ARNOLD E T,BRUCKMAIER R M.Lipopolysa
-ccharide and lipoteichoic acid induce different immune responses in the bovine mammary gland [J]. J Dairy Sci, 2011,94(11):5405-5412.
[12] SCHMITZ S, PFAFFL M W, MEYER H H D, et al. Short-term changes of mRNA expression of various inflammatory factors and milk proteins in mammary tissue during LPS-induced mastitis[J]. Domestic Animal Endocrinology, 2004,26(2):111-126.
[13] ALLUWAIMI A M, LEUTENEGGER C M, FARVER T B, et al. The cytokine markers in Staphylococcus aureus mastitis of bovine mammary gland[J]. Journal of Veterinary Medicine, Series B: Infectious Diseases and Veterinary Public Health, 2003,50(3):105-111.
[14] YANG W, ZERBE H, PETZL W, et al. Bovine TLR2 and TLR4 properly transduce signals from Staphylococcus aureus and E. coli, but S. aureus fails to both activate NF-kappaB in mammary epithelial cells and to quickly induce TNF-alpha and interleukin-8(CXCL8) expression in the udder[J]. Molecular Immunology, 2008,45(5):1385-1397.
[15] BOUGARN S, CUNHA P, HARMACHE A, et al. Muramyl dipeptide synergizes with Staphylococcus aureus lipoteichoic acid to recruit neutrophils in the mammary gland and to stimulate mammary epithelial cells[J]. Clinical and Vaccine Immunology, 2010,17(11):1797-1809.
[16] WELLNITZ O, REITH P, HAAS S C, et al. Immune relevant gene expression of mammary epithelial cells and their influence on leukocyte chemotaxis in response to different mastitis pathogens[J]. Veterinarni Medicina,2006,51(4):125-132.
[17] RAINARD P, FROMAGEAU A, CUNHA P, et al. Staphylococcus aureus lipoteichoic acid triggers inflammation in the lactating bovine mammary gland[J]. Veterinary Research,2008,39(5):52.
[18] RAMBEAUD M, ALMEIDA R A, PIGHETTI G M, et al. Dynamics of leukocytes and cytokines during experimentally-induced Streptococcus uberis mastitis[J]. Veterinary Immunology and Immunopathology,2003,96(3):193-205.
[19] WELLNITZ O, BERGER U, SCHAEREN W, et al. Mastitis severity induced by two Streptococcus uberis strains is reflected by the mammary immune response in vitro[J]. Schweiz Arch Tierheilkd,2012,154(8):317-323.
[20] BANNERMAN D D. Pathogen-dependent induction of cytokines and other soluble inflammatory mediators during intramammary infection of dairy cows[J]. Journal of Animal Science, 2008,87(13):10-25.
[21] LEE J W, BANNERMAN D D, PAAPE M J, et al. Characterization of cytokine expression in milk somatic cells during intramammary infections with Escherichia coli or Staphylococcus aureus by real-time PCR[J]. Veterinary Research, 2006, 37(2):219-229.
[22] LAHOUASSA H, MOUSSAY E, RAINARD P, et al. Differential cytokine and chemokine responses of bovine mammary epithelial cells to Staphylococcus aureus and Escherichia coli[J]. Cytokine,2007,38(1):12-21.
[23] WENZ J R, FOX L K, MULLER F J, et al. Factors associated with concentrations of select cytokine and acute phase proteins in dairy cows with naturally occurring clinical mastitis[J]. Journal of Dairy Science, 2010,93(6):2458-2470.
[24] SURIYASATHAPORN W, SCHUKKEN Y H, NIELEN M, et al. Low somatic cell count:A risk factor for subsequent clinical mastitis in a dairy herd[J]. Journal of Dairy Science, 2000,83(6):1248-1255.
[25] DJABRI B, BAREILLE N, BEAUDEAU F, et al. Quarter milk somatic cell count in infected dairy cows: A meta-analysis[J]. Veterinary Research, 2002,33(4):335-357.
[26] BANNERMAN D D, PAAPE M J, GOFF J P, et al. Innate immune response to intramammary infection with Serratia marcescens and Streptococcus uberis[J]. Veterinary Research, 2004,35(6):681-700.