Active enhancement in the primate by bone marrow I. Ia-like determinants on nucleated bone marrow cells

This study investigates the possibility that the active enhancing properties of bone marrow (BM) cells may be related to Ia-like determinants on their surface membranes. Less chromium was released on a cell per cell basis from nucleated baboon BM cells used as targets in complement-dependent cytotoxicity than from labelled lymph node lymphocytes. On the other hand, BM cells stimulated allogeneic lymphocytes in culture more vigorously than lymph node lymphocytes. BM cells with lymphocyte-activating properties could be enriched by fractionation on a discontinous bovine serum albumin gradietnt. BM cells responded poorly to allogeneic cell stimulation in mixed culture. Platelet absorption studies of an alloantiserum supported the conclusion that nucleated BM cells, and particularly BM fractions collected from the less dense interfaces of a bovine serum albumin gradient, express relatively more lymphocyte-activating or Ia-like determinants than "serologically defined" determinants.