Alteration of T cells and natural killer cells during chickenpox in infancy.

To determine the reasons for the low immune response and the mild morbidity of chickenpox in infancy, we investigated alteration of T cells and natural killer (NK) cells during chickenpox in children < 1 year and > or = 2 years old using flow cytometry. The CD4/CD8 ratio decreased only in the < 1-year-old group from the acute to the convalescent phase (P < 0.05). The CD3-CD16+CD56+ and CD57-CD16+ counts increased in the < 1-year-old group, but those in the > or = 2-year-old group did not increase from the acute to the convalescent phase. The CD3-CD16+CD56+ counts and the CD57-CD16+ counts and percentage were larger in the < 1-year-old group than those in the > or = 2-year-old group (P = 0.001, P = 0.002, and P < 0.05) in the convalescent phase. These results seem to indicate that the low immune response in infancy after chickenpox are related to the small number of CD8 in contrast with CD4 and that increased subsets of NK cells during chickenpox may correlate to the mild morbidity of chickenpox in infancy.