Immunohistochemical localization of d-alanine to β-cells in rat pancreas

A mouse monoclonal antibody against d-alanine (d-Ala) has been raised and the immunohistochemical localization of this d-amino acids in the rat pancreas is visualized. The obtained anti-d-Ala monoclonal antibody has no significant cross-reactivity to all proteinogenic l-amino acids and their d-enantiomers. Using this antibody, immunohistochemical staining was performed on the pancreas, and specific staining for d-Ala has been observed only in the Langerhans islets. To identify the types of d-Ala-immunopositive cells, double staining was carried out with antibodies against d-Ala and pancreatic hormones. Similar immunostaining patterns have been observed for d-Ala and insulin, while d-Ala is hardly co-localized with other hormones (glucagon, somatostatin, and pancreatic polypeptide). These results indicate for the first time that d-Ala is localized to insulin producing β-cells in mammalian pancreas, suggesting that this d-amino acid would be involved in the regulation of the blood glucose level.