免疫系統是任何生物中最重要的系統之一。由免疫系統所引起的免疫反應保護了生物免於外來病原體例如：寄生蟲、細菌和病毒所帶來的威脅和有害物質。對於人類和許多脊椎動物來說，複雜的免疫系統基本上能夠分成兩個主要的子系統：先天免疫系統和後天免疫系統。在這篇研究中，藉由斑馬魚在白色念珠菌的初次感染和二次感染之時間序列微陣列數據，我們分別建立了在初次感染和二次感染下的斑馬魚蛋白質調控網路。由分析每個網路中的節點蛋白質和比較兩個網路中有顯著連線數差異的蛋白質，我們辨識出細胞凋亡程序是重要的功能性模組，並且在初次感染中，細胞凋亡是被促進的，而在二次感染中，細胞凋亡是被抑制的。由這些發現，我們推論出由病原體所引起的細胞凋亡在初次感染中是相對活躍的，因為在初次感染下，斑馬魚引起的免疫反應並不夠有效率。然而，由宿主引起的細胞凋亡，免疫記憶性使得宿主免疫系統在二次感染中能夠去針對病原體作更準確的反應。因此，細胞凋亡在初次感染中是促進的，但在二次感染中是被抑制的。
我們的分析能夠幫助更進一步的了解有關於細胞凋亡在斑馬魚先天免疫和後天免疫中扮演的角色。我們相信這些觀點能夠使得在對抗傳染病這場永不止息的戰爭中，在提供治療和藥物設計上有更大的進展。

Immune system is one of the most important biological systems in every living organism. The defensive mechanisms incurred by the immune system protect the organism from potential threats or the harmful substances caused by the foreign pathogens such as parasites, bacteria and virus. For human and many vertebrates, the complicated immune system can basically be categorized into two main subsystems: the innate and adaptive immune system. In this study, based on the time-course microarray data of zebrafish in its primary and secondary infection by C. albicans, we constructed two zebrafish intracellular PPI networks for the primary and secondary infection, respectively. By inspecting the hub proteins of each network and by comparing the significant changes of the number of linkages between the two constructed PPI networks, we identified the process of apoptosis as one of the main functional modules that is activated for the primary infection and inhibited for the secondary infection. Based on our findings, we postulated that pathogen-induced apoptosis is relatively more active during primary infection since immunity responses triggered by zebrafish under primary infection are not efficient enough. For host-induced apoptosis, however, the immunological memory enables the host immune system to response to the pathogen more precisely during secondary infection. Hence, apoptosis is activated during primary infection but inhibited during secondary infection. Our in silico analyses help pave the foundation for further investigation on the interesting roles played by apoptosis on innate and adaptive immunity for zebrafish. We believe that such insights could lead to therapeutic advances and drug design for the never-ending battle against infectious diseases.

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