Age-associated Increase in Expression of the T Cell Surface Markers Thy-1, Lyt-1, and Lyt-2 in Congenitally Athymic (nu/nu) Mice: Analysis by Flow Microfluorometry

The expression of T cell-associated surface markers by lymphoid cells from congenitally athymic (nude) mice has been quantitatively investigated using flow microfluorometry. Spleen and lymph nodes from old (greater than 6 mo) nude mice on either a C57BL/6 or BALB/c genetic background were found to contain significant numbers (5 to 13% in spleen and 15 to 24% in lymph nodes) of cells expressing Thy-1 antigen. The proportion of Thy-1 positive cells in nude spleen was dramatically increased (to 22 to 67%) after passage of the cells over nylon wool columns. In contrast to older animals, young (1- to 2-mo-old) nude mice had undetectable levels (less than 1%) of Thy-1 bearing cells in spleen and reduced levels (6%) in lymph nodes. After passage of their spleen cells over nylon wool, some Thy-1 positive cells (10%) were detectable in 2-mo-old nude mice but none were detectable at 1 mo. In addition to Thy-1, we were able to detect the T cell alloantigens Lyt-1 and Lyt-2 on nylon wool-passed spleen cells from older C57BL/6 or BALB/c nu/nu mice. In general, the proportion of Lyt-1 bearing cells in nude lymphoid populations was similar to the proportion of Thy-1 positive cells. A smaller fraction of nude cells (corresponding to 35 to 59% of the total Thy-1 positive cells) were found to express Lyt-2. Analysis of the forward light scatter distributions of nude lymphoid cells bearing either Thy-1, Lyt-1, or Lyt-2 antigens further demonstrated that an overlapping population of relatively large-size cells expressed these surface markers. These data strongly imply that at least 2 subsets of T cells (i.e., Lyt-1+2- and Lyt-1+2+) develop in older nude mice in the apparent absence of thymic influence.