Serum inhibitors of myelopoiesis.

A modification of the microcytotoxicity assay of Terasaki & McClelland was used to screen for serum inhibitors of myeloid progenitor cells (CFU-C). Sera from 104 patients with neutropenia or bone marrow failure and from 104 controls, including 30 normal subjects and 74 patients with various disorders or multiple transfusions, were studied. Inhibitors of CFU-C were found in 19 of the 104 patients with neutropenia or marrow failure: three with acquited neutropenia and 16 with aplastic anaemia. In 17 of the 19 patients the inhibitor was either complement dependent or chavincingly associated with clinical remission of disease in one patient. In another patient, the inhibitor was an IgG antibody directed against non-HL1 antigens present on CFU-C of all 50 normal target marrows tested; however, it was not clearly autoreactive. Inhibitors were also found in one of nine patients with lupus erythematosus, one with breast carcinoma, one patient with renal transplant rejection, and six of 46 multiply transfused patients without marrow failure. Our findings indicate that most serum inhibitors are associated with multiple transfusion: convincing evidence of pathogenetically important autoreactive antibody was present in only one of 19 patients with inhibitors.