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Even though a detailed understanding of the proliferative characteristics of T lymphocytes is imperative in many research fields, prior studies have never reached a consensus on these characteristics, and on the corresponding cell cycle kinetics specifically. In this study, the general proliferative response of human T lymphocytes to phytohaemagglutinin (PHA) stimulation was characterized using a carboxyfluorescein succinimidyl ester-based flow cytometric assay. We were able to determine when PHA-stimulated T lymphocytes complete their first division, the proportion of cells that initiate proliferation, the subsequent division rate of the cells, and the impact of irradiation on these proliferative properties. Next, we accurately visualized the cell cycle progression of dividing T lymphocytes cultured in whole blood using an adapted 5-ethynyl-2’-deoxyuridine pulse-chase method. Furthermore, through multiple downstream analysis methods, we were able to make an estimation of the corresponding cell cycle kinetics. We also visualized the impact of X-rays on the progression of the cells through the cell cycle. Our results showed dose-dependent G2 arrest after exposure to irradiation, and a corresponding delay in G1 phase-entry of the cells. In conclusion, utilizing various flow cytometric assays, we provided valuable information on T lymphocyte proliferation characteristics starting from first division to fully dividing cells.

Background: Both standardized and non-standardized candida skin tests are used in clinical practice for functional in-vivo assessment of cellular immunity with variable results and are considered not reliable under the age of 1 year. We sought to investigate the reliability of using manually prepared candida intradermal test in the evaluation of T cell function in infants during their second year of life. Methods: Twenty-five healthy infants were tested with manually prepared intradermal candida test. Cultured lymphocytes were stimulated with phytohemagglutinin (PHA) and gamma interferon (IFN-γ) levels were measured in the culture supernatant of stimulated and non-stimulated samples using ELISA. Results: The enrolled infants were 14 to 24 months old (mean 19.2 ± 3.13 months). They were 17 boys (68 %) and 8 girls (32 %). Candida skin test was positive in 17 out of the 25 infants (68%). All infants showed increased IFN-γ levels after PHA stimulation (mean ± SD: 0.83±0.29 ng/ml) compared to basal levels (mean ± SD = 0.16 ± 0.16 ng/ml). The increase of IFN γ levels after PHA stimulation ranged from 1.54 to 38 folds. Infants with positive and negative candida tests showed comparable results in terms of clinical and immunological assessment except for weight percentiles for age that were higher among candida positive group. Conclusion: Candida intradermal test is a cost-effective simple test for evaluation of T cell function with 70 % sensitivity in healthy infants above the age of one year. Keywords: Candida, IFN-γ, infants, intradermal, lymphocyte proliferation, PHA stimulation, T cell, Tuberculin