FIG 6.

MHV68 latency decreases the number and alters the phenotype of virus-specific secondary memory CD8⁺ T cells. Ten-week-old naive C57BL/6 mice were i.n. infected with 10⁴ PFU of MHV68 or medium. Thirty-five days postinfection, mice were challenged with serum-free RPMI or 2 × 10⁵ PFU of LCMV Armstrong i.p. On day 35 post-LCMV Armstrong infection, mice were injected with 2 × 10⁶ PFU of LCMV clone 13 i.v. (A) Splenocytes were harvested on day 5 post-secondary infection and stained with anti-CD8α, anti-CD44, and the indicated MHC class I tetramer. The number of CD8⁺ tetramer⁺ cells is plotted. (B) Three thousand naive P14 cells were adoptively transferred into naive or latent hosts and then infected with LCMV Armstrong. On day 35 postinfection, 2.0 × 10⁴ memory P14 cells were purified and then adoptively transferred into naive hosts. These animals were then challenged with 5 × 10³ CFU. Listeria monocytogenes cells expressing GP33-41 and P14 cells were enumerated on day 5 in the spleen. The average and standard deviation are plotted. (C) LCMV-specific CD8⁺ T cells were quantitated in the spleen on day 60 post-clone 13 secondary challenge. The number of antigen-specific CD8⁺ T cells is plotted. (D) The percentage of increase in primary to secondary LCMV-specific memory CD8⁺ T cells was determined. The expression of CD27 and CD62L (E) and CD127 and KLRG1 (F) was determined and quantitated on secondary memory CD8⁺ cells. In each plot, the average is indicated by the horizontal bar. *, significant difference between mice infected with LCMV and mice infected with both LCMV and MHV68 (P ≤ 0.05). Four to six mice were harvested in two independent experiments.