Comparative Response of Normal Human Thymus and Lymph Node Cells to Phytohemagglutinin in Culture

Human thymocytes, in short-term tissue culture, show a proliferative activity distinct from that observed by either lymph node or blood lymphocytes.As expected, the behavior of lymph node lymphocytes in culture is very similar to that of peripheral blood lymphocytes. The only difference betweenthese 2 groups of cells was the finding of spontaneous proliferation by normal lymph node cells after 3 days in culture without phytohemagglutinin(PHA).

Whereas blood and lymph node lymphocytes show a negligible uptake ofH3T in the basal state, approximately 10 per cent of thymus cells incorporateH3T, indicating significant autonomous proliferation. This is unaffected byPHA and is unassociated with globulin synthesis as judged by immunofluorescent technics. After 3 days in culture, there are significantly more transformed cells and more cells which incorporate H3T into DNA in thymus cellcultures containing PHA than in the control cultures. However, the labelingindex of stimulated thymus cultures is less than either the basal rate of proliferation of thymocytes or 3-day cultures of PHA stimulated blood and lymphnode lymphocytes. These observations suggest that the normal human thymuscontains at least two populations of lymphoid cells: a major component whichshows autonomous and unsustained proliferative activity and does not respondto PHA, and a second and probably minor cellular component which transforms and proliferates in response to PHA.

Submitted on August 25, 1966 Accepted on October 24, 1966