Intrinsic factor (IF), also known as gastric intrinsic factor (GIF), is a glycoprotein produced by the parietal cells of the stomach. It is necessary for the absorption of vitamin B12 later on in the ileum of the small intestine. The glycoprotein binds free B12 in the ileum and the IF-B12 complex is then recognized by the cubam receptor complex facilitating receptor-mediated endocytosis. In humans, the gastric intrinsic factor protein is encoded by the GIF gene. 

Intrinsic factor is also produced by E.coli bacteria. But in humans, IF is not provided by E.coli.