Production of human bone marrow-derived suppressor factor. Effect on antibody synthesis and lectin-activated cell proliferation

Natural suppressor cells resident in normal human bone marrow (BM) exert potent suppressor activity on in vitro antibody responses and other immune functions. A suppressor-enriched population of BM cells can constitutively produce a soluble mediator with similar suppressor activity and kinetics as the suppressor cells. This novel BM-derived suppressor factor (BDSF) suppresses human in vitro primary antibody responses as well as lectin-activated proliferative responses. The mediator (BDSF) has a Mr of less than 1.5 kDa, contains a lipid component, and is insensitive to indomethacin treatment. The BM cells producing the factor bear the HNK-1 surface marker but not T, B, or macrophage markers. The ability of BDSF to suppress Ag-dependent IgM responses during the inductive phase makes it an ideal molecule with the potential to regulate early immune and hemopoietic events within the BM compartment.