therefore part of the body's system?

therefore part of the body's system = therefore (block) the function of a part of the body's (immune) system?

Context:

The explanation seems to lie in a protein called SOCS3, which blocks the function of T-cells – a type of immune cell and therefore part of the body's system for fighting infection. At the beginning of an acute infection, SOCS3 becomes highly activated, suppressing the body's immune response. That sounds just the opposite of what you'd want. But it's a good thing because it stops T-cells being overzealous, which can cause damage to body tissue, says Pellegrini.

More:

http://www.newscientist.com/article/dn20086-hivlike-infection-banished-from-mice.html