T-large granular lymphocyte frequencies and correlates in disease states detected by multiparameter flow cytometry in pediatric and young adult population.

T-large granular lymphocytes (T-LGL) characterized by dim CD5 staining, although not completely understood, have unique roles in the immune system. Expansion of peripheral blood (PB) clonal T-LGL populations is associated with various entities in adults. We have previously demonstrated clonal T-LGL proliferations in pediatric immune dysregulation/inflammatory/proliferative conditions. However, T-LGL populations have not been studied in broader spectrum pathologies. In this study we evaluated sizes and correlates of T-LGL populations in the pediatric and young adult populations with various disease states. Lymphocytes including T-LGL were investigated retrospectively by reviewing PB multiparameter flow cytometric data with various indications over a 4-year period. Associations with clinical, laboratory findings, and T-LGL population sizes were sought. Among 520 cases reviewed, 240 were females and 280 males with a mean age of 9 years (0-33 years); mean T-LGL population constituted 14% (1-67%) in PB T cells. There were significant differences between T-LGL and CD5-bright, regular T cells. T-LGL correlated with CD8 + /DR + (R = 0.570; P < 0.01) and CD8 + /CD11b + (R = 0.597; P < 0.01) expression, indicating activated cytotoxic phenotype. The highest average T-LGL were seen in bone marrow transplant recipients (23.7%), Evans syndrome (23.7%), lymphoma (20.6%), and acute EBV infection (20.4%) cases, all with underlying immune dysregulation pathologies. In pediatric and young adult patients with different clinical conditions, PB T-LGL constitute an average of 14% of the T cells and have a predominantly activated cytotoxic T cell phenotype. Higher relative presence was seen in cases with an immune dysregulation background. These results may serve as a reference for T-LGL research efforts.