Human thymus cells: blastogenic response to mitogens, antigens and allogeneic cells

Over 90 per cent of the thymus cells from each of twenty-six donors were T lymphocytes, identified by E-rosetting and less than 3 per cent of the cells were B lymphocytes identified by EAC-rosetting. With advancing age, the proportion of T lymphocytes decreased while that of B lymphocytes increased. The degree of (3H)thymidine incorporation of thymus cells was inversely proportional to the age of the thymus-cell donor. The PHA or PWM- induced blastogenic response of thymus cells gradually increased with advancing age when the response was expressed as the stimulation index. However, the actual rate of (3H)thymidine incorporation in all three groups was rather similar when cells were cultured with mitogens. The difference in stimulation index was due to the variation in incorporation rate in cultures without stimulants. The PHA response was approximately four-fold higher than that of PWM response. Thymus cell response to allogeneic lyphocytes, on the other hand, had no correlation with the age of thymus donor. The most surprising result in the present study was that the thymus cells from each of ten donors, aged 1-14 years, were incapable of responding to all four different recall antigens. Peripheral blood lymphocytes from nine to ten randomly selected age-matched children responded very well to one or more antigens.