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INTRODUCTION Quantification of lymphocyte subpopulations is useful for evaluating immune response in states of health and disease, including immunodeficiencies, autoimmunity, infections and cancer. Studies have found that concentrations and proportions of different cell subpopulations vary with geographic location, age, sex and ethnicity. Knowing the normal values of these cells and their variation in healthy populations will contribute to improved clinical practice and scientific research. OBJECTIVE Estimate normal absolute concentrations and percentages of the most abundant lymphocyte subpopulations in peripheral blood and their relation to sex and age. METHODS A cross-sectional analysis was conducted in 129 healthy adults, 61 men and 68 women aged 18-80 years; 89 aged <50 years and 40 ≥50 years. We included individuals who agreed to participate by written informed consent. Exclusion criteria were chronic disease, or use of tobacco, alcohol or medications that can alter immune system cell numbers and functions. Through dual platform flow cytometry, we determined absolute and percentage values for T lymphocyte subsets CD3+, CD3+/CD4+T, CD3+/CD8+T, CD19+ B cells and CD3-/CD56+ natural killer cells in peripheral blood, using an 8-color flow cytometer. We estimated medians and the 2.5 and 97.5 percentiles and calculated the Pearson correlation coeffi cient to evaluate associations. Significance tests were also used to compare groups. The significance threshold was p = 0.05 in all cases. RESULTS Ranges of absolute values and percentages (%) were: total lymphocytes: 1200-3475 cells/μL (20.2-49.3); CD3+ T cells: 880-2623 cells/μL (56.5-84.7); CD3+/CD4+ T cells: 479-1792 cells/μL (30.3-55.7); CD3+/CD8+ T cells: 248-1101 cells/μL (13.2-42.9); CD19+ B cells: 114-1491 cells/μL (5.4-49.5); CD3-/CD56+ natural killer cells: 70-652 cells/μL (3.7-28.0); and the CD4+:CD8+ index: 0.80-3.92. Absolute numbers--but not percentages--of lymphocytes and CD3+ T cells were higher in those <50 years (p = 0.025 and 0.020, respectively). Absolute values and relative percentages of CD3+/CD8+ and relative values of CD3+/ CD4+ T cells were significantly higher in the younger subgroup (p = 0.004 and p = 0.047). Age was not associated significantly with B lymphocytes or natural killer cells. Absolute and relative values of CD3+/CD4+ T lymphocytes were significantly higher in women (p = 0.009 and 0.036, respectively). CONCLUSIONS. Absolute numbers of total lymphocytes and T and CD3+/CD8+ T lymphocytes are higher in younger individuals. In percentage values, CD3+/CD4+ T lymphocytes are lower in older persons. Absolute and percentage values of CD3+/CD4+ T phenotype are higher in women. These differences justify adjusting clinical analyses to different values by age and sex. [ABSTRACT FROM AUTHOR]

INTRODUCTION Flow cytometry allows immunophenotypic characterization of important lymphocyte subpopulations for diagnosis of diseases such as cancer, autoimmune diseases, immunodeficiencies and some infections. Normal values of rare lymphoid cells in blood, quantified by cytometry, vary among different populations; so it is indispensable to obtain normal national values that can be used in clinical practice. OBJECTIVE Characterize distribution of rare T-lymphocyte populations in peripheral blood, specifically double-positive T, natural killer T and activated T lymphocytes, as well as their relationship to sex and age. METHODS A cross-sectional study was carried out in 129 adults (68 women, 61 men) aged >18 years, without chronic diseases or unhealthy habits, who signed informed consent. Peripheral blood was collected for immunophenotyping of lymphocyte subpopulations with monoclonal antibodies specific for CD4+CD8+ double-positive T cells, CD3+CD56+ natural killer T cells, and CD3+CD25+HLA-DR+ activated T cells. An eight-color flow cytometer (Beckman Coulter Gallios) was used. The analytic strategy was modified, associating variables of interest in a single graphic, using conventional monoclonal labeling antibodies. Medians and minimum and maximum percentiles (2.5 and 97.5, respectively) were used as descriptive statistics, stratified by sex, for cell counts and percentages. A linear regression model was applied to assess age effects and a two-tailed Mann-Whitney U test for independent samples was used to assess sex differences. The significance threshold was set as p ≤ 0.05. RESULTS Median percentages of total lymphocytes: natural killer T cells 6.3% (1.4%-23%) in men and 4.7% (0.8%-11.3%) in women (p = 0.003); activated T cells 1.0% (0.2%-2.2%) in men and 1.2% (0.4%-3.1%) in women, without statistical significance; and double positives 0.8% (0.1%-4.2%) in men and 0.9% (0.3-5.1) in women, also without statistical significance. Median cell counts (cells/mL) were: natural killer T cells, 126 (27-580) in men and 105 (20-279) in women (p = 0.023); activated T cells: 20 (4-46) in men and 25 (7-75) in women, (p = 0.013) and double-positive T cells: 17 (2-85) in men and 21 (7-154) in women, without statistical significance. Sex influenced natural killer T cells, but age did not. CONCLUSIONS Age does not affect counts and percentages of rare T lymphocyte subpopulations in the blood of healthy Cuban adults. Sex differences found for some phenotypes suggest the need for different reference values for women and men. [ABSTRACT FROM AUTHOR]