Whoever keeps it up for first year one can protect (8)
I believe the answer is:
antibody
'whoever' is the definition.
I can't judge whether this definition defines the answer.
'it up for first year one can protect' is the wordplay.
I cannot quite see how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found in the answer.
'first' could be 'i' (I in Roman numerals eg Elizabeth I) and 'i' is found in the answer.
'year' could be 'y' and 'y' is present in the answer.
'one' could be 'an' (an apple is one apple) and 'an' is found within the answer.
The remaining letters 'bod' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'keeps' acts as a link.
Can you help me to learn more?
(Other definitions for antibody that I've seen before include "Protein produced in the blood" , "Antigen attacker" , "Pathogen fighter" , "personal protection" , "Protective protein in blood which destroys inimical substances" .)