The nature of the adherent hemopoietic cells in human long-term bone marrow cultures (HLTBMCs): presence of lymphocytes and plasma cells next to the myelomonocytic population.

An immunological analysis of the nonmacrophage hemopoietic cells in the adherent layer of human long-term bone marrow cultures was performed in situ. It revealed not only the expected granulocytic and monocytic cells, but an important lymphoid population as well. The latter consisted of cells bearing the markers of mature T lymphocytes, B lymphocytes, and plasma cells. These cells were also present in the hemopoietic foci of the adherent layer, the so-called cobblestone areas. Although more CD8+ than CD4+ lymphocytes were generally present in the initial bone marrow inoculum, both the adherent layer and the nonadherent fraction disclosed a preponderance of CD4+ cells after a short period of culture. The majority of the lymphoid cells were present in the adherent layer, rather than in the nonadherent fraction of the cultures. The long-term presence of lymphoid elements in the adherent layer suggests their affinity for the bone marrow stroma and the possible enhancement of their persistence in vitro by contact with these cells.