Furthermore, expression of the activation marker KLRG1 was elevated in naive and EM CD8+ T cells but not CD4+ T cells (Figure 2E), whereas expression of the proliferation marker Ki-67 was increased in naive CD4+ and CD8+ T cells as well as CM CD4+ T cells in the maternal SARS+ group (Figure 2E). Here, MKI67 is linked to severe acute respiratory syndrome.