Cell interactions influencing murine marrow megakaryocytes: nature of the potentiator cell in bone marrow

Auxiliary bone marrow cells are required for optimal murine megakaryocyte colony formation in addition to progenitor cells and a colony stimulating activity (CSA) present in WEHI-3 cell conditioned medium. These auxiliary cells are adherent, with a sedimentation rate of 5.8 mm hr-1 and buoyant density of 1.065–1.078 gcm-3. The activity from bone marrow cells is loss at irradiation doses above 900 rad. Bone marrow cells with these characteristics, and supernatants from lung, bone shafts, and peritoneal exudate cells were all active in enhancing megakaryocyte colony incidences in mouse bone marrow cultures above those stimulated by an obligatory activity in WEHI-3 cell conditioned medium. Certain macrophage cell lines (J774, P388D1) could elaborate the activity. This study confirms that a potentiation activity enhances CSA stimulation of megakaryocyte colony formation. The potentiator is elaborated by bone marrow cells in limiting amounts requiring either high cell concentrations or an exogenous source of the activity for optimal colony growth.