Kinetics of 21-trisomic lymphocytes. I. In vitro response of 21-trisomic lymphocytes to PHA

Data presented here on the quantitative 3H-thymidine incorporation into DNA, after PHA mitogenic stimulation, show that 21-trisomic lymphocytes are low-responders to PHA compared with the normal-diploid ones. Their responsiveness seems to decrease with the donor's age. Auto-radiographic studies clearly demonstrate that the fraction of labeled cells at the 72nd h of incubation is significantly smaller in the 21-trisomic lymphocyte population. The comparison of labeling indexes at different times of incubation (24, 48, 72 h) also indicate, in the same population, a slower increment of the portion of DNA-synthesizing cells. Discussing these data in the light of other's observations and recent progress in the knowledge of factors and mechanisms involved in the lymphocyte response to lectin mitogenic stimulus, it is suggested that differential distribution of T- and B- and/or T-cell subpopulations and a retarded cell induction time to proliferate may be two important factors negatively influencing the responsiveness of 21-trisomic lymphocyte population.