|
實驗性自體免疫腦炎 (experimental allergic encephalomyelitis;
EAE) 是一種經由免疫佐劑混合髓鞘鹼性蛋白 (myelin basic protein;
MBP) 刺激後所誘發的一種去髓鞘性疾病﹐主要的病徵是在中樞神經系統
內血管周圍會有發炎性損傷。 在目前亦被當成研究人類之多發性硬化
症(multiple sclerosis; MS) 的實驗動物模式。 小鼠的實驗性自體免
疫腦炎可在具敏感性的品系如﹕SJL/J (H-2s), PL/J (H-2u)及 B10.PL
(H-2u) 等以髓鞘抗原混合佛闌式完全佐劑 (complete Freund''s
adjuvant) 加百日咳桿菌 (Bordetella pertusis) 為輔助佐劑致敏化後
誘發之。 相對地, 實驗性自體免疫腦炎並無法在其它大多數品系的小鼠
以上述方式被誘發。 不過﹐在我們實驗室先前的研究卻發現﹐經過腹腔
注射(i.p.) 免疫佐劑混合髓鞘鹼性蛋白之再刺激後﹐腦內注射 (i.c.)
髓鞘鹼性蛋白可在多種原為具抗性品系如C57BL/6等小鼠造成實驗性自體
免疫腦炎。 其臨床症狀在腦內注射後兩天最為明顯，且有白血球浸潤到
腦膜下、血管周圍及腦脊髓實質部等組織病理變化。 在腦內注射後的十
二小時內，浸潤的發炎細胞主要是嗜中性白血球；二十四小時後則大部份
為單核淋巴球所取代。 目前文獻報告多認為頸部淋巴結擔任腦和週邊免
疫系統之間溝通的管道﹐與腦內免疫反應之發生相關。 我們也發現頸部
淋巴結的細胞數目會隨著實驗性自體免疫腦炎的發展而有動態變化。 且
頸部淋巴結細胞也比四肢部位淋巴結細胞對髓鞘鹼性蛋白刺激有較高的增
生反應。 此外﹐在頸部淋巴結與腦內均可見到一群很不尋常的 CD4-
CD8-CD3+Vb8+ T 細胞次族群出現。 這些細胞可經體外培養而增多﹐同
時其TCR Vb8的表現量亦會 增加。 另外﹐以持續表現 b-
galactosidase 之大腸桿菌當作追蹤物去測定腦-血管障壁通透性之變化
﹐可發現在腦內注射六小時後腦-血管障壁呈現開啟狀態。 於腹腔或腦
內注射後﹐許多腦內微血管內皮細胞表面亦有ICAM-1及VCAM-1等
integrins分子表現。 在發炎的鼠腦並可偵測到Fas及其配體的表現﹔且
以原位 (in situ) terminal deoxytidyltransferase 反應亦可見到凋亡
的浸潤發炎細胞。 由鼠腦中細胞素訊息RNA表現之時程分析﹐在病程發展
的早期﹐腦內的細胞素訊息 RNA表現類型屬於所謂的Th0類型﹔腦炎
症狀最明顯時﹐則偏向Th1類型﹔到了疾病回復期﹐僅剩IL-10 仍持續表
現﹐而呈現Th2類型為主的反應。 對細胞素蛋白質之免疫組織染色則發現
不同細胞素之位置分佈亦有差異﹔如 IL-4 和 IFN-g主要是染在腦內血管
內皮細胞， 而IL-12則是染在浸潤的發炎細胞。 綜合以上結果﹐我們認
為腹腔內注射會將具自體反應性 (autoreactive) 的細胞再度活化﹐而腦
內注射則造成腦-血管障壁通透性之改變﹐加以ICAM-1及VCAM-1等
integrins分子在腦內血管內皮細胞的表現﹐導致此類細胞得以從血管浸
潤到腦內﹐最後引起自體免疫腦炎。 此外﹐CD4-CD8-CD3+ T 細胞之參與
﹑浸潤發炎細胞的凋亡與腦內Th1、Th2類型免疫反應之間的平衡﹐亦均在
實驗性自體免疫腦炎的調控佔有相當重要的地位。
|
|
Experimental allergic encephalomyelitis (EAE) is a demyelinating
diseasethat characterized by perivascular inflammatory lesions
in central nervoussystem. Murine EAE can be induced by an
active immunization with myelin basic protein(MBP) in complete
Freund''s adjuvant(CFA) and Bordetella pertussiscoadjuvant in
susceptible strains of mice. Three commonly used susceptible
strains are SJL/J (H-2s), PL/J (H-2u), andB10.PL (H-2u), while
resistant strains are C57BL/6 (H-2b), AKR (H-2k), and BALB/c
(H-2d), etc. However, we foundthat another intraperitoneal(i.
p.) MBP/CFA and intracerebral (i.c.) MBP restimulation in
addition to the standard protocol would induce EAE in resistant
C57BL/6 mice. Clinical symptoms would develop 2 days after the
i.c. injection. The histopathological observation manifested
cellular infiltration by leukocytes in perivascular spaces,
cerebral cortex and spinal cord. The neutrophils were prominent
at 12 h after i.c. injection, then were replaced by mononuclear
cells 24 h later. Cervical lymph nodes serves as a connection
between the brain and the peripheral immune system. The
cervical lymphatics had dynamic changes during the development
of EAE with regard to the the cell number between cervical and
distal lymph node cells. The cells derived from cervical lymph
nodes had higher MBP-stimulated proliferation than that of
distal lymph nodes. An unusual lymphocyte subset with CD4-CD8-
CD3+Vb8+ phenotype was found either in cervical lymph nodes or
in brain. These cells can be enriched after in vitro culture,
together with the upregulation of TCR Vb8. Using b-
galactosidase expressing E. coli as tracer, X-gal staining
showed that the blood-brain barrier was opened at 6 h after i.c.
challenge. The ICAM-1 and VCAM-1 adhesion molecules that
mediate the migration of leukocytes increased after i.p. or i.c.
restimulation. Interestingly, FasL as well as Fas expressionwas
also found on the inflammatory brain, and apoptotic cells were
detected by in situ hybridization. Furthermore, the kinetic
analysis of cytokine expression was done by RT-PCR and
immunohistochemistry. In the early phase of EAE, the cytokine
profiles in brain showed an so-called Th0 type. The predominant
Th1 pattern was accompanied with active disease. IL-10 was the
only cytokine remaining high expression during the recovery of
EAE. The immunoreactivity of anti- IFN-g and IL-4 mAb were
mainly observed on endothelial cells, while the infiltrated
cells showed high immunoreactivity of anti-IL-12 mAb. Taken
together, we hypothesize that the i.p. stimulation reactivates
the autoreactive T cells. The i.c. injection of MBP might have
changed the permeability of blood- brain barrier and enhanced
ICAM-1 and VCAM-1 expressions on cerebral endothelium.
Theseevents resulted in inflammatory cell infiltration including
autoreactiveT cells and the development of EAE. Besides, CD4-
CD8-CD3+, apoptosisof infiltrated cells and the Th1/Th2
interactions might also be involvedin the regulation of EAE.
|
