Erythrocytes transfused into patients with SLE and haemolytic anaemia lose complement receptor type 1 from their cell surface.

Erythrocyte complement receptor type 1 (CR1) shows a numerical deficiency in patients with SLE and with haemolytic anaemias. This receptor is a cofactor for the enzymatic degradation of C3b and is believed to play a role in the transport of immune complexes from the circulation to the reticulo-endothelial system. Erythrocyte CR1 was enumerated on cells which had been transfused into patients with SLE and haemolytic anaemias. In three patients with active disease up to 60% of CR1 was lost from erythrocytes during 5 days after blood transfusion and up to 410 molecules of C3 were deposited on these cells. These are the first in vivo data showing that CR1 may be lost from circulating erythrocytes. This acquired deficiency of CR1 on erythrocytes may have pathological consequences in patients with SLE.