They can be seen as blue-blooded lines (5)
I believe the answer is:
veins
'blue-blooded lines' is the definition.
The definition and answer can be both related to communication as well as being plural nouns.
Perhaps they are linked in a way I don't understand?
'they can be seen as' is the wordplay.
I cannot really understand how this works, but
'as' could be 'in' (I've seen this in other clues) and 'in' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for veins that I've seen before include "Circulation aids" , "Blood vessels" , "Characteristic styles" , "Layers of ore" .)