One of the adaptive immune system’s primary jobs is to recognize foreign substances in our bodies and unceremoniously reject them by eliciting inflammation. So the fact that it lets about 100 grams of assorted foreign animal and plant proteins pass through our digestive systems every single day with nary a peep is curious—food allergies are an exception.
The most common explanation given for this “oral tolerance” is that immune cells that react to proteins in food are generated but are then preferentially killed or somehow inactivated. But most of the experiments leading to this conclusion were done with transgenic mice that have a severely depleted T cell repertoire and thus lack a normal immune response. New work published in Nature uses mice with a normal, functioning immune system to recheck this result.
https://arstechnica.com/science/2022/07/why-dont-most-foods-cause-allergies/