α-Casein can be an immunogen in young children, and anti-α-casein antibodies have strong cross-reactivity with insulin. This effect can explain the uncommon insulin autoimmunity, but it does not appear to progress to Type I diabetes.
Casein sodium salt from bovine milk is a phosphoprotein. There are four main types of Casein which make up approximately 80% of the total protein in bovine milk: α-s1 Casein, α-s2 Casein, β-Casein, and κ-Casein. Casein is proposed to be the main protective constituent in milk.