KLRG1 and diphtheria: Diphtheria-specific antibody concentrations negatively correlated with the mean fluorescence intensity (MFI) of p21 in all BMMCs (p = 0.0487), as well as with the percentage of CD8+CD57+and CD8+KLRG-1+ BM T cells expressing p21 (p = 0.0043 & 0.0013 respectively) (Fig. 5a-c, upper panels).