Modification of the mixed leukocyte reaction with various antisera

Age-related changes in in vitro and in vivo survival of murine CFU-S and CFU-c

Present evidence suggests that the proliferative potential of most cell types declines with age. An apparent exception to this is the erythroid and myeloid colony-forming cell (CFU-S) of the marrow. In an effort to reveal a latent proliferative defect in old marrow, CFU-S from the marrow of young and old B6AF1 mice were serially transplanted every 12 days into lethally irradiated young syngeneic hosts. Contrary to expectation, it was found that the number of CFU-S declined more slowly if the marrow had been obtained from old donors. Similarly, it was found that CFU-S, but not CFU-c, from old marrow replicated or were recruited more vigorously in long-term culture than CFU-S from young donors. The results obtained with anti-Thy 1.2 serum and complement treatment of old marrow cells suggest that CFU-S from old marrow replicate more vigorously because old marrow has more theta + helper cells or the old CFU-S is more responsive to theta + helper stimuli.

The presence of Thy-1 on the surface of rat lymphoid stem cells and colony-forming units

By labeling Thy-1-positive cells of rats with xenoanti-Thy-1 or mouse alloanti-Thy-1 antibody and separating them from Thy-1-negative cells on a fluorescence-activated cell sorter, it was shown that early lymphopoietic stem cells all carry Thy-1-antigen. This was so for both young, adult bone marrow and near-term fetal liver cells. Two kinds of assay were used: long-term radiation chimeras employing B and T cell alloantigens to mark cells of donor origin, and in vivo colony-forming units in the spleens of irradiated recipients (bone marrow only). Thy-1-negative cells gave essentially no B or T progeny, even 6 to 12 months after reconstitution of the chimeras. The kinetics of appearance of Thy-1-positive cells in rat marrow, which peaked at 6-8 weeks of age, were also studied. In rats, Thy-1 is on the surface of pluripotent stem cells and on early progenitors of both B and T lymphocytes.

Proliferation of B and T cells in mixed lymphocyte cultures

Electrophoretically fractionated CBA/Ca spleen T cells alone respond to allogeneic cells in one-way MLC and to PHA. They do not respond to E. coli LPS. B cells alone do not respond to allogeneic cells nor to PHA, but do respond to LPS. When karyotypically distinguishable syngeneic mixtures of T and B lymphocytes are stimulated with allogeneic cells, at the most 5% of mitoses on 5-9th culture day are of B cell origin. This indicates that B cells are not substantially recruited to proliferate in the MLC.