Allo-Ia reactive murine T-cell lines. II. Mechanisms of clonal expansion of T cells explored by use of the allo-Ia reactive T cell clones.

Murine T cell clones, which were retrieved from an A.TH anti-A.TL(lak) T cell line and had been long-term cultured in the medium supplemented with T cell growth factor (TCGF) and mitomycin C(MMC)-treated feeder cells of either Is or Ik haplotype, were found to survive in TCGF-free medium for a long time, quite in contrast to so far reported TCGF-dependent T cell clones. When T cells of these clones at the full growth in the TCGF-medium were transferred to TCGF-free medium, they survived at resting state for a long time, and half-life, i.e., the time when 50% of the transferred cells were still viable, of some clones reached 20 days. The cloned T cells at the resting state retained full responsiveness to the specific lak antigen but lost the responsiveness to TCGF as determined by [3H]thymidine uptake, whereas the same T cells harvested from TCGF-medium did not show the antigen-specific responsiveness. The cloned T cells at the resting state showed marked DNA synthesis in response to the specific antigen but never entered the phase of the cell division. Addition of TCGF to the antigen-activated cloned T cells at their peak DNA synthesis triggered the cell division without time lag. Thus, it was confirmed at a single clone level that two sequential signals, one via the antigen-receptor reacting with specific antigen and another via the TCGF-receptor accepting TCGF, are required for clonal expansion of T cells reacting with antigen. The mitogen-responsiveness among five clones was examined at their resting state; two clones responded to Con A and PHA only in the presence of accessory cells (MMC-treated, T cell-depleted syngeneic spleen cells), and one clone responded well to Con A and PHA in the absence of accessory cells. Thus, most of our clones retained physiologic characteristics of T cells directly collected from mice even after long-term culture in TCGF-medium.