Increased count of CD56^dim NKG2A⁺ KIR⁻ CD57⁻ NK cells during acute IM is caused by preferential proliferation. (A) Representative examples of costaining for NKG2A and Ki-67 and costaining for KIR and Ki-67 on CD56^dim NK cells in healthy control and IM-acute and 1-month patients. (B) Frequencies of Ki-67⁺ cells within the CD56^bright, CD56^dim NKG2A⁺ KIR⁻, and CD56^dim NKG2A⁻ KIR+ NK-cell subsets in healthy controls (n = 21), in IM-acute (n = 15), and in 1-month patients (n = 7). (C) Correlation of EBV DNA loads (copies per 10⁶ PBMCs) and frequencies of Ki-67⁺ cells within the CD56^dim NKG2A⁺ KIR⁻ NK-cell subset from acute IM patients. Spearman r = 0.53, P (2-tailed) = .042. (D) Representative example of costaining for CD57 and Ki-67 on CD56^dim NKG2A⁺ KIR⁻ NK cells in an IM-acute and 1-month patient. (E) Frequencies of Ki-67⁺ cells within the CD56^dim NKG2A⁺ KIR⁻ NK cells according to CD57 expression in healthy controls (n = 15), IM-acute (n = 9), and 1-month (n = 4) patients. (F) Count of CD56^dim NKG2A⁺ KIR⁻ CD57⁻ in healthy EBV-negative controls (n = 14), healthy EBV-positive controls (n = 17), IM-like (n = 11), IM-acute (n = 17), 1-month (n = 10), and 6-month (n = 8) patients. Horizontal lines indicate median values of a given symbol. Mann-Whitney U tests.