How much gluten can damage villi in my intestines if I am diagnosed with celiac disease?

more than 20 ppm* in the case of celiac disease. It means that all gluten-free products must contain gluten in the amount less than 20 ppm.
100 ppm* is the limit for those intolerant of gluten (which is not an autoimune reaction)
*ppm (particles per milion) = mg/kg