3.3 CD8α+ T-cell subsets responded differently in domestic pigs and wild boar

CD8α+ lymphocytes are known mediators of immunity during ASFV infection . Being the largest group of CD8α+ lymphocytes, we investigated CD8α+ T-cell frequencies among αβ T cells. Frequencies of CD4/CD8α+ αβ T cells increased in blood, spleen, lungs, and liver of domestic pigs (Figure 2A). The increase was most prominent in spleen, lung, and liver of infected animals and was significant 5 or 7 dpi until the end of the trial. In the blood, we detected increased frequencies of CD8α+αβ T cells 10 dpi only. CD4/CD8α+αβ T cells in wild boar demonstrated a comparable course, except for the lung. There were no frequency alterations of CD4/CD8α+ αβ T cells in ghLN of both subspecies (Figure 2A).
Frequencies of CD4+/CD8α+ double positive (DP) αβ T cells showed a similar but less pronounced pattern (Figure 2B). Domestic pigs had elevated levels of DP T cells 5 and 7 dpi in spleen and liver, correlating with increased levels of CD4/CD8α+ αβ T cells in the same samples (Figure 2A, B). We also found increased frequencies of DP αβ T cells in the lungs and ghLN 7 dpi. There were no significant changes in the blood. In wild boar, we found increased DP αβ T-cell frequencies 5 dpi in the liver, 5 and 7 dpi in the lungs and 7 dpi in the blood (Figure 2B). Alterations in both subspecies were only temporary, as DP T cell frequencies returned to baseline levels in all animals 10 dpi.
γδ T cells are also known to express CD8α upon activation and differentiation into CD2+/ CD8α+effector cells . We did not detect any changes in effector γδ T-cell frequencies in the investigated tissues in domestic pigs (Figure 3). In contrast, effector γδ T-cell frequencies in wild boar increased in spleen 5 and 7 dpi, and 7 dpi in lung. Most pronounced and persistent increases were found in the liver of infected animals 4 to 7 dpi (Figure 3). Comparable to DP αβ T cells, the changes were not permanent and effector γδ T-cell levels returned to control levels 10 dpi.
We also analyzed Ki-67 expression as a marker for proliferation in the second trial. We found pronounced proliferation of CD8αα+ and CD8αβ+ T cells in domestic pigs as well as in wild boar 10 dpi (Figure 4A, B). Proliferating cells were primarily found 10 dpi, but elevated frequencies of Ki-67+ CD8αα+ and CD8αβ+ T cells were also found 7 dpi in the spleen of domestic pigs. Regarding CD4+ αβ T cells, we found significantly increased frequencies of proliferating CD4+/CD8α T cells only in the spleen of both suid species 7 dpi. Moreover, DP T cells in domestic pigs proliferated significantly 7 and 10 dpi, again only in spleen (Supplemental figure 1). In contrast, we did not find Ki-67+, proliferating γδ T cells in domestic pigs or wild boar (data not shown).