Relationship between apoptosis and thymocyte depletion in rabies-infected mice

The apoptosis of thymocytes from rabies-infected mice was investigated in a kinetic study covering the entire course of the infection. For this study, BALB/c mice (6-7-week old females) were inoculated intracerebrally with 100 LD50 of Challenge Virus Strain, a fixed rabies virus strain, and three animals were sacrificed per time point to remove thymuses. When thymocytes were fixed, stained with propidium iodide and analyzed by flow cytometry, a distinct subpopulation of cells was observed below the G0/G1 region, denoted as the A0 region. Cells in this region presented reduced fluorescence, and nuclear DNA fragmentation. The accumulation of cells in the A0 region, after infection, progressively increased, reaching 12% for unfractionated thymocytes, 62% for thymocytes from the 60% Percoll interface and 32% for thymocytes recovered at the 100% Percoll interface. This finding, observed only in thymocytes from infected mice, demonstrates a clear modification of chromatin condensation in these cells, suggesting the occurrence of an apoptotic process during rabies infection.