Elevated CD3(low) double negative T lymphocyte is associated with pneumonia and its severity in pediatric patients

BACKGROUND: Previous studies have shown that the adaptive immunity function of T cells in disease states correlates with CD3 surface expression closely. During routine assessment of TBNK subsets in peripheral blood of pediatric patients by flow cytometry, we noticed that variable expression levels of CD3 on CD3(+)CD4(−)CD8(−) double-negative T (DNT) lymphocytes in different patients. The objective of this study was to assess the relationship of CD3 expression levels on DNT cells with disease severity. METHODS: In this prospective study, we investigated the frequencies of circulating CD4(−)CD8(−) DNT cell subsets with CD3(low) or CD3(high) phenotype by flow cytometry in 76 pediatric patients with pneumonia, 55 patients with severe pneumonia (SP), and 29 healthy controls (Con). RESULTS: The numbers of circulating DNT cells were similar in all groups; however, the frequency of CD3(low) DNT cell subsets was significantly increased in patients with pneumonia (p < 0.001) and SP (p < 0.001). The elevated CD3(low) DNT cell frequency showed a positive correlation with the clinical severity of pneumonia. On sub-group analysis, the frequency of CD3(low) DNT cells was only elevated in children with pneumonia aged <5 years, while no association was observed with the causative pathogen of pneumonia. CONCLUSIONS: These findings suggest that CD3 expression levels on DNT cell subsets of peripheral lymphocytes may be a valuable biomarker for evaluation of immune response in pediatric infectious disease. CD3(low) DNT cells were elevated in children with pneumonia aged <5 years, which indicates that it may be an important research target in pediatric infectious diseases.