CFU-C inhibitors in aplastic anaemia.

Peripheral blood lymphocytes from 15 patients with marrow aplasia were tested for their ability to inhibit the proliferation of normal granulopoietic precursor cells (CFU-C) in agar culture, relative to the inhibitory effect of normal lymphocytes studied in parallel. Eight of the 15 patients with marrow aplasia had lymphocytes which were significantly less inhibitory to normal CFU-C than controls whereas 3 patients had lymphocytes which were significantly more inhibitory. Two further patients who had recovered from marrow aplasia were also studied. The effect of patient's plasma and normal plasma on normal CFU-C proliferation was also studied and in 1 case a potent inhibitor of granulopoiesis was demonstrated. In 9 cases CFU-C could be cultured from patient's marrow, and parallel studies examining the effects of lymphocytes or plasma on patient's CFU-C were performed in these. All 9 patients had low numbers of marrow CFU-C. In none of the 9 marrow samples tested was inhibition by patient lymphocytes significantly greater than normal controls. The results highlight the heterogeneity inherent in the study of aplastic states and serve to underline the importance of controls. In only a minority of cases (20%) was lymphocyte suppression of normal granulopoiesis by lymphocytes from patients with aplastic anaemia significantly greater than normal lymphocyte suppression.