Cell phenotypes and differentiative transitions in mouse submandibular salivary gland defined with monoclonal antibodies to mammary epithelial cells.

Recognition of distinct cell phenotypes within a given organ is important in defining cell relationships during development and in analyzing the role of cell-cell and cell-matrix interactions in growth and differentiation. Phenotypic definition of dissociated heterogeneous cell populations is also essential for studies on mechanisms regulating expression of cell lineage-specific gene products. Mouse submandibular salivary gland (SSG) cell phenotypes in the course of differentiative transitions in vivo and after enzymatic dissociation in primary culture were defined with monoclonal antibodies (MAb) to mammary epithelial cells and polyclonal antibodies to functional cell products. Proacinar cells and differentiating and mature acinar cells were uniquely recognized by an MAb designated 50B8. Ductal cell components were uniquely recognized by an MAb designated JSE3. JSE3 immunoreactivity was particularly useful for detecting the emergence of two SSG duct cell phenotypes, striated ducts and the hormone-responsive granular convoluted tubules (GCTs). JSE3-positive striated duct-like cells were visualized as early as Day 2 after birth and emergence of GCT-like structures from striated ducts was apparent between Days 10 and 11. Differential reactivity of acinar and ductal cells in the developing SSG with either MAb 50B8 or JSE3 suggests the existence of intermediate progenitor cells restricted in their differentiation potential. An interesting pattern of immunoreactivity was observed with an MAb designated 33A10. During the first 2 weeks of SSG postnatal development, shared 33A10 immunoreactivity was observed among proacinar and differentiating acinar cells and all differentiating ductal segments. Coincident with a decrease in proliferative activity at about Day 18, 33A10 immunoreactivity became restricted to the GCT cell lineage before the appearance of GCT functional products, epidermal and nerve growth factors. Although the SSG antigen recognized by MAb 33A10 is presently undefined, its expression pattern suggest a molecule with a dual role in development and growth events and in hormone-dependent secretory function. Advantage was taken of the observed differential immunoreactivities to define the phenotypic identity of dissociated, mature SSG cells before and after culture. Dissociated SSG fractions enriched for either JSE3- or 50B8-positive cells could be maintained in short-term cultures without loss of expression of duct- or acinar cell-specific immunoreactivity. In addition to providing markers for defining dissociated SSG cells before and after culture, the described immunoreactivities may permit separation or enrichment of an early duct cell population before its commitment to a specific cell lineage. This approach may also provide the means to define regulatory signals involved in the differentiation of intermediate progenitor cells.