Serologic identification of early members of the T cell lineage

The SC-1 antigen, identified by thymus-absorbed rabbit anti-mouse brain antiserum, is present on multipotential stem cells. Its presence on cells of the T lineage has been examined by immunofluorescence, and we have demonstrated that it is also a marker for thymic development. Although it is present on the majority of fetal and neonatal thymocytes, its expression declines rapidly and, as early as 1 mo after birth, adult levels are reached. In normal animals, these do not change during adult life, even in mice destined to develop a T cell leukemia. SC-1 does reappear transiently on cells in the regenerating thymus of sublethally irradiated mice. Although the antigen is not associated with preleukemic changes in the thymus, it is expressed on some cells of all spontaneous T lymphomas, and it is uniformly present on tissue culture lines of T cell lymphomas.