Natural killer-like cells produce the cell-directed inhibitor of monocyte leukotaxis, CDI-MLx, in vitro.

The leukotactic responsiveness of human peripheral blood monocytes is regulated by the cell-directed inhibitor of monocyte leukotaxis, CDI-MLx. Normal peripheral blood mononuclear cells elaborated CDI-MLx in vitro in response to soluble and cell-associated antigens; concanavalin A and pokeweed mitogen induced production of the inhibitor while phytohemagglutinin and staphylococcal protein A were without effect. By erythrocyte rosetting and immunoadherence, the CDI-producing cell had the phenotype, E-rosette+, OKMI+, and Leu 7+, and thus appeared related to natural killer cells. PBMC and plasma CDI-MLx had similar molecular weights (230,000) and showed similar heterogeneity on chromatofocusing with peaks of activity at pH 5.8 and 5.25. CDI-MLx was immunologically distinct from immunoglobulins, did not inactivate preformed leukotaxins, and was distinct from other lymphokines known to modulate monocyte locomotion.