Sites of localization and synthesis of Ss protein in mice

Ss, a serum protein whose structure and level in serum are determined by genes of the mouse H 2 complex, was localized to a variety of cell types, using immunofluorescence and radiolabel techniques. Peritoneal macrophages and liver parenchymal cells appeared to synthesize Ss for export to serum. These cells stained in the cytoplasm for Ss and released labeled Ss into the medium of cultures fed ¹⁴C amino acids. Other cultured cells, fibroblasts of Ss high strains, bore the protein only on their membranes. The membrane bound form of Ss had at least one antigenic determinant masked; this determinant was exposed when membrane associated Ss was released into culture medium. At least in some cells Ss, like the other products of H 2 region genes, is membrane associated.