Soluble complement receptor 1 is increased in patients with leukemia and after administration of granulocyte colony-stimulating factor

Complement receptor type 1 is expressed by erythrocytes and most leukocytes . A soluble form is shed from the leukocytes and found in plasma (sCR1). sC R1 is a powerful inhibitor of complement, We report an increased sCR1 in th e plasma of leukemia patients, up to levels producing measurable complement inhibition. Half of the 180 patients with acute myeloid leukemia (AML), ac ute lymphoblastic leukemia (ALL), and chronic lymphocytic leukemia (CLL) ha d sCR1 levels above the normal range. The highest levels were observed in T -ALL (1? patients). The complement function of a T-ALL serum was improved b y blocking sCR1 with a specific mAb (3D9). Measurements in 16 peripheral st em cell donors before and after granulocyte colony-stimulating factor (G-CS F) administration showed an increase in sCR1 (before, 43.8 +/- 15.4; at day 5, 118.3 +/- 44.7 ng/mL; P < 0.0001). This increase paralleled the increas e in total leukocyte counts and was concomitant with de novo leukocyte mRNA CR1 expression in all three individuals tested. Whether pharmacological in tervention may be used to up-regulate sCR1 so as to inhibit complement irt vivo should be further investigated.