Heterogeneity of pathogenetic mechanisms in aplastic anemia. Efficacy of therapy based on in-vitro results.

The mechanisms responsible for the bone marrow failure in 21 aplastic anemia patients were studied by the colony-forming units in culture assay (CFU-C). Twelve patients had no detectable in-vitro defect that could be responsible for the low CFU-C numbers. Three patients had suppressor T cells that inhibited CFU-C (p less than 0.001); one of two patients responded to antithymocyte globulin therapy and the third recovered spontaneously. Three patients had serum inhibitory immunoglobulins directed against their marrow CFU-C; plasmapheresis resulted in recovery of bone marrow function. Three patients had abnormalities at the colony-stimulating factor level: Two had inhibitors of colony-stimulating factor, corrected in vitro and in vivo by indomethacin and cholinergic agonists (p less than 0.01); and the third had colony-stimulating factor generation defect, corrected in vitro and in vivo by lithium. Testing for cellular or humoral suppressor factors directed against precursor cells or for abnormalities at the colony-stimulating factor level gives helpful guidelines to therapy in aplastic anemia.