Fig. 4

Diphtheria-specific antibody concentrations correlated with CD8⁺CD57⁺ T cells (a), CM CD8⁺ T cells expressing PD-1 (b), and CM CD4⁺ T cells expressing PD-1 (c) in the BM (upper panels), and in the PB (lower panels). CM: central memory T cells (CCR7⁺CD45RA⁻). Correlation coefficients (r_p) and significances were calculated according to Pearson with correction for age