Different subsets of T cells in the adult mouse bone marrow and spleen induce or suppress acute graft-versus-host disease.

Fractionation of normal adult mouse spleen and bone marrow cells (C57BL/Ka) was performed by discontinuous Percoll density gradients. The fractionated low density (1.050-1.060 g/ml) C57BL/Ka spleen cells completely suppressed acute lethal graft vs host disease (GVHD) when coinjected with unfractionated C57BL/Ka spleen cells into sublethally irradiated (400 rad) BALB/c mice. In dose response experiments, as few as 0.5 x 10(6) low density cells from the spleen fractions suppressed acute GVHD induced by 2.5 x 10(6) unfractionated allogeneic spleen cells. Although the low density spleen fractions inhibited acute GVHD, the high density (1.075-1.090 g/ml) spleen fractions induced acute GVHD in sublethally irradiated BALB/c recipients. Fractionation of C57BL/Ka bone marrow cells showed that none of the high or low density fractions or unfractionated cells induced lethal GVHD. When these fractions were tested for their capacity to suppress GVHD by coinjection with C57BL/Ka unfractionated spleen cells, all fractions protected the BALB/c recipients. Unfractionated bone marrow cells showed modest protection. Evaluation of the dose response characteristics of the suppressive activity of the low and middle density (1.060-1.068 g/ml) bone marrow cell fraction showed that reproducible protection could be achieved at a 5:1 ratio of inducing to suppressing cells. The low density fractions of both bone marrow and spleen cells had a marked depletion of typical TCR(+)-alpha beta CD4+ or CD8+ T cells, and a predominant population of TCR(+)-alpha beta CD4- CD8- T cells. Purified populations of the latter cells suppressed GVHD. Recipients given unfractionated C57BL/Ka spleen cells and protected with low-density bone marrow or spleen cells were chimeras.