Immunoglobulin synthesis and secretion by cells in the mouse thymus that do not bear theta antigen

The mouse thymus contains cells that synthesize and secrete minute amounts of immunoglobulin (Ig). These cells were studied by a combination of cytotoxic tests (with alloantisera prepared in congenic strains of mice) followed by pulse labeling of the surviving cell population with [(3)H]tyrosine. The immunoglobulin-synthesizing cells constitute less than 2% of the total cell population and are theta(-), TL(-), Ly-B(-), Ig(+), H-2(+), and PC(+). Since this phenotype is not characteristic of cells of the thymocyte lineage, the Ig(+) cells are probably plasma cells and/or bone marrow-derived (B) lymphocytes. Similar studies of spleen cells indicate that immunoglobulin-synthesizing and secreting cells are theta(-).