hce_nthu
113年
生物與生化
第 28 題
Which of the following statements about Trypanosomes and their interaction with hosts and the immune system is correct?
- A Trypanosomes have a simple life cycle that involves only one host and does not require a vector for transmission.
- B The primary mechanism of immune evasion in Trypanosomes is the constant change of their surface glycoproteins (VSGs) through gene rearrangement, allowing them to avoid detection by the host's immune system.
- C The gene rearrangement in Trypanosomes is triggered by the host's immune response, leading to a temporary suspension of VSG production and a dormant state in the parasite.
- D Coevolution with humans has led to Trypanosomes becoming less virulent, resulting in a symbiotic relationship where the parasite does not harm the host.
- E The immune system of secondary hosts, such as tsetse flies, plays a crucial role in the suppression and elimination of Trypanosomes, preventing their transmission to humans.
思路引導 VIP
想像一下，如果人體的免疫系統就像是一個持有「通緝令」的警察，正在血液中根據特定的「外貌特徵」（抗原）追捕寄生蟲。如果這群寄生蟲想要在防守嚴密的血液中長期生存，而不被警察徹底清除，你認為它們在遺傳機制上，必須具備什麼樣的「變裝」能力？這種變裝是應該在被警察發現後才開始準備，還是應該在族群中不斷自主更新？
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AI 詳解
AI 專屬家教
太棒了！你能精準選出 (B)，代表你對寄生蟲如何與宿主免疫系統「鬥智」有著深刻的理解。這題展現了生物學中極為精妙的分子機制：抗原變異 (Antigenic Variation)。
寄生蟲的分子偽裝術
錐蟲（Trypanosomes）之所以棘手，是因為它們擁有一套龐大的基因庫，編碼成千上萬種不同的變異表面醣蛋白 (VSGs)。透過精密的基因重組機制，錐蟲能像變色龍一樣，在免疫系統產生抗體辨識出當前「外衣」時，隨機切換表達另一種全新的 VSG。這使得宿主好不容易建立的免疫防禦瞬間失效，造成血液中蟲體數量呈現週期性的消長，讓感染難以根除。
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