New research suggests that tobacco not only promotes cancer development， but also helps early cancer cells evade detection① by the immune system， which might otherwise mop up harmful cells before they reproduce and spread.
Cells exposed to tobacco have fewer substances on their surfaces used to signal whether or not the cell is dangerous and should be destroyed by the immune system. As such， cells with fewer of these warning devices， if they become cancerous， would be more likely to evade detection by the immune system， grow and spread throughout the body.
The cellular warning devices are known as HLA class 1 molecules②， which are usually unique to each person. These molecules sit on the surface of cells and present a protein③ to the outside environment. If this protein is derived from harmless substances inside the cell， immune system components known as killer T cells will bypass the cell， considering it to pose no threat to the body. However， if the protein inside a class 1 molecule was made as a result of a cancer inside the cell， or comes from a virus， the T cells hone in on the cell and destroy it.
Cells exposed to tobacco showed fewer HLA class 1 molecule. Cells exposed to tobacco show lower levels of a particular protein that forms a link in the chain that assembles HLA class 1 molecules inside the cell. Reductions in this protein， known as TAP1， likely lead to lower amounts of HLA class 1 on the cell surface.
These changes do not cause cancer， but simply allow the cancer to thrive in the body once it appears.
The class 1 is gone before the cell becomes cancerous④. If those cells become cancerous， there isn’t enough class 1 for T cells to kill them.
All tobacco-containing substances—not just those that people smoke—would likely have the same effect. If you just sucked on a cigarette it could do this to you. Cigarettes are bad for your health.
① detectionn. 发现，发觉；侦查；探知；【无】【电视】检波
② moleculen. 【化】【物】分子；微小颗粒
③ proteinn. 蛋白质，朊 adj. (含)蛋白质的
④ cancerousadj. 癌的；像癌的；步步扩散的
烟草与癌细胞
新的研究表明，烟草不仅会促进癌症的发展，而且还能帮助早期的癌细胞逃避人的免疫系统的检测，而这种检测有可能在癌细胞繁殖和扩散之前就将其消灭。
细胞接触烟草后，其表面的一些物质减少了，而正是这些物质可发出细胞是否有危险以及免疫系统是否应该将其消灭的讯号。由于细胞报警能力的降低，一旦细胞发生癌变，它们就很有可能逃避人体免疫系统的监测而繁殖起来，并扩散到全身。
这种细胞报警构造叫做HLA 1 组分子，在通常情况下，每一个人的HLA 1 组分子都是独特的。这些分子位于细胞的表面，向周围环境发出一种蛋白质。如果该蛋白质来自于细胞中无害的物质，免疫系统中一种被称为T细胞杀手会认为它们对人体不构成威胁而将其放行。然而，如果HLA 1 组分子内的蛋白质是由细胞癌变所产生的，或来自于病毒，T细胞就会围剿和消灭它们。
接触过烟草的细胞含有较少的HLA 1 组分子，接触过烟草的细胞内有一种特殊蛋白质的含量降低了，该蛋白质在细胞内可形成“流水线”来组装HLA 1 组分子。一种被称为TAP1蛋白质的减少很可能导致了细胞表面HLA 1 组分子的含量降低。
这些变化本身不会造成癌症，但是可以在癌症发生时，允许其在体内肆无忌惮。
在细胞癌变前，HLA 1 组分子已减少。如果这些细胞发生癌变，就会造成HLA 1 组分子含量不足，致使T细胞不能消灭癌细胞。
不仅是人们所抽的烟草，所有含有烟草的物质都有可能具有同样的效果。只要你抽烟，就可能有此危险。香烟对健康有害。
