The PD-1/PD-L1 Pathway Affects the Expansion and Function of Cytotoxic CD8(+) T Cells During an Acute Retroviral Infection

David, Paul; Megger, Dominik A.; Kaiser, Tamara; Werner, Tanja; Liu, Jia; Chen, Lieping; Sitek, Barbara; Dittmer, Ulf; Zelinskyy, Gennadiy

Previous studies showed high expression of PD-1 on the surface of effector CD8 + T cells from acutely FV-infected mice (4, 28) . These FV induced activated CD8 + T cells (CD69 + , CD44 + , CD62L − ) were defined by their expression of a glycosylated form of the CD43 molecule (29) . To test whether the deficiency for the PD-1/PD-L1 pathway influences acute T cell immunity, wild type (WT) C57BL/6J mice, PD-1 −/− and PD-L1 −/− mice were infected with FV. In these mice the effector CD8 + CD43 + T cells and CD8 + T cells specific for the H-2Db-restricted Friend murine leukemia virus-glycosylated immundominant gag epitope (tetramer + ) (18) were characterized. Spleen and bone marrow (BM) are the organs with the highest virus replication during the acute phase of FV infection (14) . Both these organs were analyzed on days 0 (uninfected), 4, 6, 7, 8, 10, 12, and 15 after FV inoculation. The expansion of effector CD8 + CD43 + T cells in WT mice and both knockout (KO) mouse strains started at day 6 after infection ( Figure 1A) . However, in KO mice the frequencies of T cells with effector phenotypes were enhanced in the spleen at day 6 after infection. It is interesting that in the BM the population of effector CD8 + T cells expanded two days later at day 8 after infection ( Figure 1B) . At day 10 after FV infection effector CD8 + CD43 + T cell numbers peaked in both organs of all analyzed mouse strains with the exception of FIGURE 1 | Expansion of effector CD8 + T cells and FV loads during acute infection of mice without PD-1 signaling. C57BL/6, PD-1 −/− and PD-L1 −/− mice were infected with FV and splenocytes and bone marrow were isolated at different time points after infection. Flow cytometry was used to detect the numbers of effector CD8 + T cells in spleen (A) and in bone marrow (B) expressing the activation associated glycoform of the CD43 molecules. The numbers of effector CD8 + specific for the FV gagL epitope were determined in spleens (C) and bone marrow (D). Viral loads were determined in spleen (E) and in bone marrow (F). Mean numbers plus SD of 5-9 mice are shown. Data was pooled from three independent experiments with similar results. One-way ANOVA with a Tukey post-test was used for the comparison of both KO mice strains with WT animals at every analyzed time point. Statistically significant differences between the groups (blue for comparison with PD-1 −/− and red for comparison with PD-L1 −/− ) are indicated (*p < 0.05, **p < 0.005, ***p < 0.0005).