Any mammal's inherant immunity is reliant on many factors, 'The Compliment System' being one of the first and most important.
'Compliments' bind to anti-bodies, creating a catalyst to speed up an immune response and faciliate anti-bodies in targeting certain bacteria.
These 'compliments' are to do with proteins.
Proteins are vital for cellular repair, cellular membranes and as building blocks.
It is therefore vital that every animal obtains the correct amount of amino acids from protein in order to keep these cells and therefore the immune system healthy.
Cooking de-natures proteins. (Pond, 2003)