ACTIVATION OF MONOCYTES FOR THE IMMUNE CLEARANCE OF RED-CELLS IN BETA-O-THALASSEMIA HBE

We have recently provided evidence that IgG antibodies play a role in the destruction of red cells in thalassaemia syndromes. In order further to delineate factors involved in the clearance of thalassaemic cells, monocytes of 30 Thai patients with beta-degrees-thal/HbE (17 non-splenectomized and 13 splenectomized) and 16 normal controls were examined for their ability to bind and phagocytose normal red cells coated with IgG anti-Rh(D). In beta-degrees-thal/HbE, the mean number of red cells attached to the monocytes was approximately 3-fold greater than in normal controls and the number ingested 30% higher. Among the non-splenectomized patients, the number of red cells attached to and ingested by the monocytes, correlated inversely with mean basal Hb levels, suggesting that activation of mononuclear phagocytes for the immune clearance of red cells is a factor in determining the severity of the anaemia. As Fc-gamma-RI is of primary importance in the recognition of IgG-coated red cells by monocytes, leucocytes from 10 beta-degrees-thal/HbE patients (four non-splenectomized and six splenectomized) and five normal controls were investigated for their expression of Fc-gamma-RI by flow cytometry. In beta-degrees-thal/HbE there was an approximately 3-fold increase in the percentage of leucocytes expressing this receptor: the receptor was up-regulated on monocytes and induced on granulocytes. The up-regulation of Fc-gamma-RI in beta-degrees-thal/HbE is likely to be an important component in the activation of monocytes and in mediating their enhanced effector function towards antibody-coated cells.