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胸腺細胞是一群不成熟的 T 細胞，必需在胸腺中先經過分化成 的教育過
程，才能真正成為有功能的 T 細胞。在胸腺中的教育過 包括正向(
positive selection) 及負向(negative selection) 選隉C經由正向及負
向選擇的過程，分別可以讓胸腺細胞認得自己的HC 分子，及剔除一些基
因重組不全亦或是有缺陷的 T 細胞。b體外培養時，胸腺細胞會計劃性死
亡。在報告裡，我們利用體外培i的方式， 去探討造成胸腺細胞計劃性死
亡的原因。有別於其L活化引發的細胞死亡，我們發現培養液中的成分會
影響胸腺細胞漲蛣o性死亡。結果顯示，將胸腺細胞培養在不含氯化鈉的
培養液中A發現胸腺細胞不會死亡，而且維持很高的存活率；但隨著氯化
鈉濃蛌獐W高，胸腺細胞的自發性死亡也愈加明顯。另外，培養液中的鈣
髐l，碳酸氫根離子，以及培養液的酸鹼值也會影響胸腺細胞的自發呇漱'
。這些離子改變所造成的胸腺細胞死亡，可藉由外加離子通道磻謇?
DMA, Na/H 通道抑制物；DIDS, Cl/HCO3 通道抑制物；SITS,a/HCO3/CO3
通道的抑制物）而將其抑制下來。由此可知，胸腺細胞漲蛣o性死亡可能
是藉由離子通道的改變，而影響細胞內酸鹼值所致C為了進一步確定，我
們利用對酸鹼度敏感的染劑-BCECF去偵測細胞內飄P值的變化。結果發現
隨著培養液中氯化鈉濃度的增高，細胞內的飄P值也隨之增加。除此之外
，鈣離子的存在也會造成胸腺細胞內酸P值的增加。另外，我們也發現胸
腺細胞的自發性死亡，不會因為外加NA 及蛋白質合成的抑制物而將其抑
制下來。由此可知，胸腺細胞的自o性死亡，主要是透過細胞膜離子通道
的改變，影響細胞內酸鹼值所致A而其過程不需要新蛋白質的合成。除此
之外，我們也去探討胸腺細胞蛣o性死亡時的信號傳遞。發現環腺甘酸(
cAMP) 能抑制胸腺細胞的漱'；然而蛋白質激活酵素 C (PKC) 的活化卻會
促進細胞的死亡。悁馴i知，胸腺細胞的自發性死亡會受環腺甘酸及蛋白
質激活酵錕 這兩條途徑所調控。除了自發性死亡外，我們也利用這個體
外培養獐狾‘h探討 Dexamthasone 引發的胸腺細胞死亡。我們發現
examthasone 引發的胸腺細胞死亡，也會透過對細胞膜離子通道的控謘A
進而影響細胞的死亡。
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Thymocytes are immature haemopoietic cells which
willifferentiate and mature in the thymus. The thymocyte
undergoesositive and negative selection to acquire its T-cell
repertoirencluding MHC-restriction and self tolerance.
Thymocytes have aapid turnover in thymus, where thymocyte
apoptosis is aeflection of lack of positive selection rather
than negativeelection. Thymocytes cultured in vitro will also
diepontaneously via apoptosis. Other than activation-induced
celleath, extracellular factors in culture medium will
influence theell survival. In this study, we found that the
NaCl concentra-ion of the medium influenced the spontaneous
thymocyte apoptosis.hymocyte did not die if culture in
low[NaCl] condition,and thereas a [NaCl] dose-dependent
thymocyte apoptosis.The[Ca2+],[HCO3-]r pH of culture medium
also affected the spontaneous thymocytepoptosis. Furthermore,
dimethylamiloride (a Na/H antiporternhibitor),DIDS(a Cl/HCO3
exchangerinhibitor)and SITS(Na/HCO3/CO3otransporter inhibitor)
could inhibit spontaneous thymocyte apopt,ndicating that
intracellular pH might dictate the process of apophrough ion
transports of the membrane.BCECF-AM,an intracellula pHrobe,was
used to determine the pHi under various NaCl concentrat.e found
that the intracellular pH of thymocytes was more
alkalinentracellular pH of thymocytes was also increased when
cultured inresence of[Ca2+],regardless the [NaCl] of the medium.
ycloheximide and actinomycin D. Taken together these data
suggestpontaneous thymocyte apoptosis was controlled by pHi
through Na/Hntiporter,Cl/HCO3 exchanger, and Na/HCO3/CO3
cotransporter on theembrane, and the apoptotic process does no
need protein de novoynthesis.Furthermore,we also found that
forskolin and it analogue8-bromo-cAMP) could inhibit
spontaneous thymocyte apoptosis,whileMA had an opposite effect.
These results suggeste that spontaneoushymocyte apopotos was
regulated both by cAMP and PKC pathways.
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