A chemotactic inhibitor produced by blast cells and present in the serum of a patient with acute lymphoblastic leukemia.

A chemotactic factor inhibitor (CFI) was found in the serum of a patient with acute lymphoblastic leukemia. The factor was characterized as heat-labile, with activity against complement-dependent chemotactic factors and against the chemotactic factor produced by Escherichia coli. Normal sera and sera from other patients with acute leukemia also demonstrate heat-labile inhibitory activity against complement-dependent chemotactic factors but not against the E. coli-derived chemotactic factor. Supernatants from cultured lymphoblasts of the patient also possessed CFI activity similar in character to that found in his serum. It is suggested that in vivo the lymphoblasts were responsible for the chemotactic defect observed in his serum, presumably by manufacturing and releasing a chemotactic factor inactivator.