Upset in tummy seems a response by this? (6,6)
I believe the answer is:
immune system
'a response by this?' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.
'upset in tummy seems' is the wordplay.
'upset' indicates anagramming the letters.
'in'+'tummy'+'seems'='intummyseems'
'intummyseems' anagrammed gives 'IMMUNE SYSTEM'.
Can you help me to learn more?
(Other definitions for immune system that I've seen before include "The body's natural defence" , "Body's protection against diseases" , "Body's infection-fighting set-up" .)