Different functional subsets of cultured murine T cells express characteristic levels of adenosine deaminase activity

Abstract

The level of adenosine deaminase (ADA) activity in mouse T-lymphocyte cultures was studied under different growth-supporting conditions and in mixed lymphocyte culture-derived long-term T-cell lines and clones. Early after the initiation of in vitro culture, the levels of ADA (2000 U/mg) were similar in bulk cultures either depleted or not depleted in Lyt-2 + T cells. Enrichment for cytolytic T lymphocytes (CTL) obtained by addition of exogenous interleukin 2 (IL-2), was accompanied by a net decrease of ADA activity (110 ± 15 U/mg). All the tested CTL-A lines derived from such cultures were also characterized by a low or undetectable level of this enzyme (at best 160 ± 70 U/mg) as previously observed. In contrast, “Lyt-2 −” T-cell bulk cultures grown, without addition of exogenous IL-2, in the presence of γ-irradiated H-2 d stimulators maintained a constant level of ADA activity (1770 ± 340 U/mg) for at least 3 months. Functionally distinct types of Lyt-2 − T-cell lines were also analyzed: T-cell lines competent to activate B lymphocytes to growth and terminal maturation as well as others devoid of detectable functions showed a stable ADA level comparable to that expressed by the original bulk culture (1685 ± 620 U/mg). The present results demonstrate that, like tumor cell lines, most normal T lymphocytes express a high level of ADA activity in culture, which strongly suggests that the low level of ADA activity exhibited by CTL is a characteristic of this functional subset.