T cell receptor excision circles as a tool for evaluating thymic function in young children

The thymus is a primary lymphoid organ responsible for the maturation of T cells as well as the immunological central tolerance. It is in the antenatal period and infancy that it plays its major role. In clinical practice, T cell receptor excision circles (TRECs) are considered a direct and reliable measure of the thymic function. TRECs are a by-product of DNA formation in gene rearrangement of T cell receptors. They are stable and they do not duplicate during mitosis, representing the recent emigrant T cells from the thymus. Despite their importance, TRECs have been neglected by physicians and there is a lack of data regarding thymic function during infancy of healthy children. In order to evaluate thymic function in the first years of life, we propose measuring TRECs as a valuable tool. One hundred and three blood samples from children and adolescents between 3 months and 20 years of age were analyzed. The mean TRECs count was 136.77±96.7 copies of TRECs/μL of DNA. The individuals between 0 and 5 years of age had significantly higher TRECs values than those between 10 and 20 years of age. No significant difference was observed in TRECs values among age groups below 5 years of age. An inverse correlation between TRECs and age was found (r=0.3 P=0.003). These data highlight and validate the evidence of decreased thymus function with age, even during infancy. Awareness should be raised with this important albeit ignored organ.

Hematological Alterations and Thymic Function in Newborns of HIV-Infected Mothers Receiving Antiretroviral Drugs.

Objectives: To investigate the effects of antiretroviral (ARV) drugs on hematological parameters and thymic function in HIVuninfected newborns of HIV-infected mothers. Study design: Cross sectional study. Setting: Chiang-Mai University Hospital, Chiang-Mai, Thailand. Participants/Patients: 49 HIV-uninfected and 26 HIV-infected pregnancies. Methods: Cord blood samples of newborns from HIVuninfected and HIV-infected mothers were collected. Hematological parameters were measured using automatic blood cell count. T-cell receptor excision circles (TRECs) levels in cord blood mononuclear cells (CBMCs), CD4+ and CD8+ T-cells were quantified using real-time PCR. Main Outcome Measures: Hemotological parameters and thymic function. Results: Newborn of HIV-infected mother tended to have lower mean levels of hemoglobin than those of HIV-uninfected mother (137 ± 22 vs 146 ± 17 g/L, P = 0.05). Furthermore, mean of red blood cell (RBC) counts and hematocrit and median of TRECs in CD4+ T-cells in the newborns of the former were significantly lower than those of the latter [3.6 ± 0.7 vs 4.8 ± 0.6 x 1012 cells/L, P <0.001; 0.40 ± 0.07 vs 0.46 ± 0.05 L/L, P <0.001 and 0.53 (IQR: 0.03-5.76) vs 13.20 (IQR: 2.77-27.51) x 10-3 pg/μL, P = 0.02, respectively]. Conclusion: ARV drugs altered hematological parameters and thymic function (TRECs CD4+ T-cells) in HIV-uninfected newborns of HIV-infected mothers.