Monocyte-erythrocyte interaction in autoimmune haemolytic anaemia in relation to the number of erythrocyte-bound IgG molecules and subclass specificity of autoantibodies.

Monocyte-erythrocyte interaction in patients with autoimmune haemolytic anaemia (AIHA) was assessed by phagocytosis and rosette assays. In most patients, a relationship was observed between haemolysis and the phagocytosis of their own erythrocytes by allogenic peripheral monocytes. An evaluation of the number of immunoglobulins on patient erythrocytes and IgG subclasses of autoantibodies shows that in patients with only IgG1 antibody or with additional IgG2 or/and IgG4, phagocytosis was always observed when the number of erythrocyte-bound IgG molecules was above 2,000. On the other hand, in all patients where IgG3 was detectable, phagocytosis was observed even if the amount of IgG was as low as 230 molecules per erythrocyte. Similar observations were made in the rosette assay. Generally, the number of erythrocyte-bound IgG and the presence of phagocytosis were correlated with the degree of haemolysis, but there were exceptions, i.e. the amount of IgG and phagocytosis were high but there was no evidence of haemolysis, or where there was little IgG, no phagocytosis but haemolysis was present. Our data do not indicate that erythrocytes from AIHA are preferentially bound to autologous monocytes.