Immunocytochemical localization and concentrations of the alpha and gamma subunits of 7S-nerve growth factor in the submandibular gland of the mouse.

For unexplained reasons, nerve growth factor (NGF) exists in very high concentrations in the submandibular gland of the mouse. The NGF in the gland, called 7S-NGF, is a non-covalent complex of three protein subunits, named alpha-, gamma- and beta-NGF. All the known biological activity resides in the beta-NGF subunit, and previous studies have shown that beta-NGF is present in much greater concentrations in the male submandibular gland than in the female gland. The higher concentration in the male is due to the fact that beta-NGF is synthesized in the granular tubule cells of the submandibular gland. These cells are much more numerous in the male gland. In contrast to beta-NGF, neither the concentrations of alpha and gamma subunits nor their cellular localization in the mouse submandibular gland have been established. In this study, radioimmunoassays specific for alpha and gamma subunits determined that both are present in much higher concentrations in the male gland. Immunocytochemical work localized both subunits in the granular tubule cell in the male and female submandibular gland. This indicates that all the components of 7S-NGF exist in a single cell type in the gland and suggests that 7S-NGF can be formed within this cell and secreted as a complex into the saliva.