Hepatitis B · 75 million quiet housemates乙肝 · 7500 万人的沉默同居者

Place · Level 3 · Condition

病毒把存档藏进细胞核, 所以治得住却清不掉 · 伤肝的是免疫系统不是病毒 · 共餐握手不传染, 因为它需要一个破口 · 出生 24 小时内的两针, 抢在病毒归档之前 · 半年一次超声胜过任何保肝药

cccDNA · the master copy in the nucleus

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cccDNA · 藏在细胞核里的母版

Hepatitis B virus can be pinned down by drugs but almost never cleared. The reason isn't that the drugs are weak — it's that the virus has filed its master copy inside the nucleus of your liver cells.

Once the virus gets into a liver cell, the first important thing it does isn't to replicate — it's to archive. It sends its loose circular DNA into the nucleus, repairs the gaps, seals it into a fully closed little ring, wraps it in protein, and parks it alongside your own chromosomes. This thing is called cccDNA, and it is a viral mini-chromosome (Nassal 2015).

Once filed, it sits quietly in the nucleus as the master copy. Every time a new batch of virus is needed, the nucleus transcribes RNA off that master, ships it to the cytoplasm, reverse-transcribes it back into viral DNA, packages it, and ships it out.

Now look at where the drugs land. Today's first-line oral drugs (entecavir, tenofovir — the nucleos(t)ide analogues) block the reverse transcription step, i.e. the copying shop. They can push the virus in your blood below the limit of detection, which is genuinely effective. But they cannot touch the master copy in the nucleus. The master is still there, so when the drug stops, the copying shop reopens and the virus comes back (Nassal 2015; EASL 2017).

That is the molecular root of 'controllable but not curable', and it is why most people who start these drugs generally stay on them long-term.

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