Erythroid colony stimulating and inhibiting cells in peripheral blood of transfused dogs: separation of function by velocity sedimentation

We have previously shown that the addition of normal dog peripheral blood lymphocytes (PBL) to cultures of allogeneic marrow increases the number of marrow-derived erythroid colonies (EC), but that PBL from transfused dogs usually inhibit EC growth from marrow of the transfusion donor. In this study, the cells in normal dog PBL responsible for stimulating EC growth were shown to sediment in a narrow peak at 4.30 mm/hr. A similar population of stimulating cells exists in transfused dogs and can be separated, on the basis of size, from cells that inhibit EC growth. EC-stimulating cells from transfused dog PBL sediment at 3.3--5.0 mm/hr, while cells responsible for inhibition are larger and sediment more rapidly at 5.4--8.1 mm/hr. These data demonstrate that cells capable of stimulating allogeneic EC are present in transfused dogs, but their stimulating ability is masked by the presence of EC-inhibiting cells. Thus, coculture experiments designed to test lymphocyte/marrow cell interactions may miss significant but opposing effects if unfractionated cells are used.