As diphtheria antitoxin is a foreign protein.是什么意思？

As diphtheria antitoxin is a foreign protein.

白喉抗毒素是并性蛋白.

as

adv. 同样地，一样地，例如；prep. 作为，以…的身份，如

例句
As far as I can recall, Patti was a Smith.
我记得帕蒂是姓史密斯的。

diphtheria

n. 白喉；

例句
As diphtheria antitoxin is a foreign protein.
白喉抗毒素是并性蛋白.

antitoxin

n. 抗毒素；

例句
As diphtheria antitoxin is a foreign protein.
白喉抗毒素是并性蛋白.

is

vt.& vi. 是（be的三单形式；n. 存在；

例句
Bollinger 'RD' is a rare, highly prized wine.
博林格RD香槟是一种名贵的备受推崇的葡萄酒。

foreign

adj. 外国的，外交的，外来的，不相干的，[医]异质的；

例句
The Colonial Office was absorbed into the Foreign Office.
殖民部被并入了外交部。

protein

n. [化]朊，蛋白（质）；adj. 蛋白质的；

例句
Too much protein in the diet may advance the ageing process...
饮食中摄入过量蛋白质可能会加速衰老。