即使找不到機制而仍然堅持結論正確的例子並不罕見。HIV 和愛滋病就是經典的例子了。從 1984 年至今，仍未有人能解釋為甚麼 HIV 會引起愛滋病，但整個主流醫學界卻因 Durban Declaration 這種五嶽派盟主式的號令而排除所有懷疑聲音。有兩位博客質疑我的說法，於是我嘗試回覆。昨天試了一次，今天試了兩次，不果。不知是技術問題還是審查問題（我猜是前者），唯有把回覆重貼在此（並改了些錯別字及加上 hyperlinks）。
David,
I should have made it clear in my previous comment that I have not received any medical training. I am neither a medical researcher nor a physician, not even a health worker. So, don't take my words as authoritative. As a layman, I get the relevant information mostly from Dr Duesburg's website:
http://www.duesberg.com/index.html
A 2006 paper, "Predictive Value of Plasma HIV RNA Level on Rate of CD4 T-Cell Decline in Untreated HIV Infection", published on JAMA and cited in the website concludes that
"The results of our study challenge the concept that CD4 cell depletion in chronic HIV infection is mostly attributable to the direct effects of HIV replication. Future efforts to delineate the relative contribution of other mechanisms will be crucial to the understanding of HIV immunopathogenesis and to the ability to attenuate it."
To my understanding, although there have been many results showing that HIV infection is strongly correlated with low CD4 counts, the pathogenic mechanism of HIV-infection is still not understood (although there have been many attempts at explaining this). The authors of a 2007 paper, e.g., opined that
"Despite 20 years of research, we still fail to understand how human immunodeficiency virus (HIV) causes acquired immunodeficiency syndrome (AIDS)."
( http://www-binf.bio.uu.nl/pdf/Ganusov.ti07-28.pdf )
Here is the opinion of another two researchers:
"Despite almost twenty years of study and the accumulation of significant experimental insights, the fundamental mechanisms underlying HIV-induced CD4+ T cell depletion remain incompletely understood."
( http://www.jci.org/112/6/821?ck=nck&content_type=full )
Surely, these opinions may be wrong. A whole bunch of researchers and medical professionals have met in this March/April to "elucidate the molecular mechanisms of HIV infection":
http://www.keystonesymposia.org/Meetings/viewPastMeetings.cfm?MeetingID=943&CFID=2180940&CFTOKEN=36663379
I am not sure if they have clarified anything.
[I'm sorry for occupying Chainsaw's space for possibly -- please judge by yourself -- trolling on the AIDS issue.]
以上是昨天打的，不過不知是否按錯掣，無 post 到。
方潤：
我不懂醫學，無從判斷，但單從雙方的論調（不敢說「論據」—— 如前述，我不懂醫學），這次我會信賴站於壓倒性少數的那一方。
說 AIDS 不是由 HIV 引起是大話，其實不一定是這樣的。被視為異端的一方，懷疑的其實是 「HIV 是 AIDS 的唯一病因」這個假說，有些人將此簡稱為 AIDS=HIV。這個假說的對立面有很多個，例如有人認為 HIV 只是種 passenger virus，有人認為其他因素也可以引起 AIDS，也有人認為 HIV 只是 AIDS 的一個 cofactor。現時即使你抱持後兩者（比較 mild）想法也會被主流醫學界視為異端。Scientific American 只是通俗科普讀物，權威刊物如 Nature 和 Science 等根本完全封殺「異端」們的聲音。其實 'AIDS denialism' 一詞不就是預設了 AIDS=HIV 這個立場嗎？
AIDS 最尾的一個 S 是 Syndrome，是症狀，不是疾病。在美國，AIDS 的官方定義其實涵蓋了（好像是，記不清楚）29 種病症，如果某人患了這 29 種病症的其中一種而又是 HIV-positive 時，便叫 AIDS，否則便叫其他病名。譬如這 29 種病中有一種叫 KS 的癌症。如果病人有 KS 癌症而又是 HIV-positive 的話，他就是 AIDS 患者，否則便稱他為 KS 癌症患者，不管患者是否缺乏免疫力。換句話說，這個官方定義是把 HIV build-in 的，這也是為甚麼有這麼多「証據」認為 HIV 和 AIDS 有關。
也許懷疑 AIDS=HIV 的人最後是錯的，但他們起碼比主流科學家抱持更高的科學研究精神，不會在未有無可動搖的証據之前排除其他假說的可能性。純粹以科學精神來看，在 AIDS 這個 case 可以說醫學界已進入了黑暗年代。
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