Proliferation of activated thymocytes in mixed lymphocyte reactions.

Abstract

When parental strain thymocytes were transferred to heavily irradiated F1 mice large numbers of blast lymphocytes could be recovered from the thoracic duct 4 days later. This population of thymus derived thoracic duct lymphocytes (T-TDL) comprised 95–100% of donor cells (1, 2). When T-TDL were transferred to further irradiated F1 hybrid mice, syngeneic with the primary hosts, the cells entered a brief phase of DNA synthesis, reaching a peak on days 2 and 3, and falling to very low levels by day 4. In contrast, DNA synthesis was very low when T-TDL were transferred to “third party” F1 mice and was not detected in mice syngeneic with the original cell donors. This pattern differed from that observed with normal parental strain thoracic duct lymphocytes (TDL) in that TDL responded equally in the two hybrid strains and did not reach high levels of DNA synthesis until day 4 (3). These observations suggested that T-TDL, unlike TDL, could only proliferate in response to those antigens which initially provoked their formation. This conclusion was supported by the high degree of specificity manifested by T-TDL in their capacity to reject tumour and skin allografts and to lyse appropriate target cells in vitro (3).