In the vegan community there is lost of discussion of animal products causing auto immune issues. A compromised gut lining will let intact animal proteins into the body. The immune sees the animal foreigners but also attacks our body; us being animals too.
Type 1 diabetes, aka childhood diabetes, is thought to be from casein in A1 milk; where the immune system attacks the beta cells of the pancreas. Seems plausible to me; rates of dairy consumption seem to correlate with type 1. (see Finland).