Subpopulations of CD4⁻, CD8⁻ thymocytes

A population of highly purified CD4⁻, CD8⁻ thymocytes was analyzed by both flow microfluorometry and in situ hybridization in an attempt to further elucidate thymocyte subpopulations. The double-negative cells had a marked increase in expression of the c-myb and T cell gamma genes relative to unseparated thymocytes. Approximately 27% were Ly-24⁺, 8% Ly-6C⁺ and 6% 6B2⁺. All of the Ly-6C⁺ cells were also Ly-24⁺. A small population (6%) of the CD4⁻, CD8⁻ thymocytes had surface expression of the T cell receptor for antigen (F23.1); all were bright Ly-1⁺ and half were Ly-24⁺. These studies demonstrate that there are further subdivisions of the CD4⁻, CD8⁻ thymocytes based upon cell surface expression of markers previously found on bone marrow cells and their non-T cell progeny. Studies are in progress to determine whether these represent different stages of activation-maturation or different lineages of cells.