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Background: Several methods exist for flow-cytometric estimation of human peripheral blood CD4 + T regulatory cells (CD4 + Tregs). Methods:We report our experience with the estimation of human CD4 + Tregs via three different characterizations using flow cytometry (CD25 high FoxP3 + , CD25 high CD127 low/− FoxP3 + , and CD4 + CD25 high/int CD45ROFoxP3 + ) in normal subjects. We have used these methods on the control populations from two studies (32 and 36 subjects, respectively), the latter two methods retrospectively on the subjects of the first study. The six CD4 + T cell fractions obtained by the third method were differentially colored to ascertain the Abbreviations: CD45RA-RO, CD45RA or CD45RO; eTregs, effector Tregs (CD4 + CD25 high CD45RA − , or CD4 + CD25 high CD45RO + ), or active Tregs (aTregs); IPEX, immune deficiencypolyendocrinopathy-enteropathy-X-linked; iTregs, induced Tregs; mAb, monoclonal antibody; MFI, mean fluorescence intensity; nTregs, naïve Tregs (CD4 + CD25 int CD45RA + , or CD4 + CD25 int CD45RO − )

T-cell large granular lymphocyte (T-LGL) leukemia represents a clonal proliferation of cytotoxic T-cells which etiology has not been entirely elucidated. However, CD4+, CD4−, CD8−, CD4+, CD8+ cases have been described. The disease is usually characterized by cytopenias and a modest lymphocytosis. The majority of patients with T-LGL leukemia remains asymptomatic for a long period and will require treatment later during the course of their disease. Hereby we describe a case of T-LGL leukemia diagnosed by flow cytometry, which presented indolent course and required no treatment so far.

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