The invention relates to the monoclonal antibody 1G2, the hybridoma cell line H-1 G2 characterized by DSM ACC3248, and the epitope TPP comprising the amino acids threonine, proline, proline. The invention further relates to a method for producing a monoclonal antibody against a TAU protein fraction that is non-phosphorylated in positions T175 and/or T181 and/or T231. The invention also describes uses of the monoclonal antibody 1 G2 as well as an immunochemical detection system and the uses thereof. The invention finally describes the use of the immunochemical detection system for diagnosing Alzheimer's disease in humans.