Observations on rosette formation by thymocytes and T lymphocytes in guinea pigs. Effect of neonatal thymectomy, irradiation, thymosin, albumin and the influence of cell viability.

Irradiation (300 rad) of guinea pigs and subsequent transfer of bone marrow cells was followed by a decreased frequency of rabbit erythrocyte rosettes (a T lymphocyte marker) in peripheral lymphoid organs. Neonatal thymectomy did not potentiate this effect. A reduced amount of rosette-forming cells was also found in the thymus of irradiated animals. This was not affected by treatment with thymosin in vivo or in vitro, and was probably due to a reduced viability of the cells after irradiation since it was demonstrated that rosette formation among dead thymus cells was significantly less than among living cells. Incubation of normal thymocytes in non-supplemented medium for 2--4 h at 37 degrees C was also followed by a diminished rosette-forming capacity. The addition of thymosin or bovine serum albumin prevented both the decrease of rosette-forming cells and the reduction of viable cells during incubation. Thus, a diminished rosette formation may have been caused by reduced viability after incubation as well as after irradiation. The rosette-forming ability of only some dead thymocytes may reflect different subpopulations.