CD4 vs CD8 T-Cells in T1 Black Hole Formation Figure 3. FACS analysis of brain infiltrating immune cells on day 7 following TMEV infection. Figure 3A (top half) shows transfer efficiency following adoptive transfer of CD8+ splenocytes from C57BL/6 donors into RAG-1 deficient hosts. Note that with sham transfer, only 1.6% of BIL-s is CD8+ and only 0.2% recognizes VP2 epitopes, whereas transfer of CD8+ cells results in 12.6% CD8+ positivity and 2.6% positivity for VP2 peptide. The 3.3% VP2+ CD82 cells are overall unidentified, and potentially represent dead cells that bind tetramer, auto fluorescing CNS cells, dying CD8+ tetramer+ cells that have become CD82 tetramer+, or NK cells with receptors specific for class I. Figure 3B (lower half) describes transfer efficiency in our CD4 transfer experiments. With sham transfer, only 0.2% of BIL-s is CD4+, whereas with CD4 transfer, 14.4% positivity is demonstrated. doi:10.1371/journal.pone.0031459.g003 Figure 4. Differences in viral load. We measured TMEV viral load on day 7 following TMEV infection of RAG-1 deficient mice that underwent adoptive transfer of CD4 or CD8 T-cells, respectively. Overall, the viral loads aren’t different (p = 0.62) between the two groups, demonstrating that the observed T1BH formation isn’t directly related to viral load. doi:10.1371/journal.pone.0031459.g004 PLoS ONE | www.plosone.org 5 February 2012 | Volume 7 | Issue 2 | e31459