Effect of the radiolabel mediator tropolone on lymphocyte structure and function

The in vitro use of the radioisotope indium 111 (¹¹¹In) was examined as a radiolabel for lymphocytes obtained from both normal individuals and patients with a variety of lymphoid malignancies. Successful cell labeling requires a chelator. The traditional agent, oxine, has proved to be toxic to the lymphoid lineage. Cellular uptake of ¹¹¹In mediated by the chelator oxine was compared with that of a new chelator, tropolone. Oxine provided better labeling efficiency (48%) than tropolone (35%) for the labeling of normal lymphocytes. By contrast, lymphocytes from patients with chronic lymphocytic leukemia had a nearly twofold greater labeling efficiency when tropolone was substituted for oxine. Further studies demonstrated that tropolone induced functional injury to lymphocytes when mitogenic response to concanavalin A, pokeweed mitogen, and phytohemagglutinin was assessed. Similar toxicity was found when tropolone was compared with oxine. In addition, tropolone produced damaging structural changes seen by both scanning and transmission electron microscopic examination. These changes were both variable and not predictable. Shortening of the incubation time of the chelator with the cell provided the least amount of cellular injury. These findings suggest that tropolone be used as an alternative mediator of lymphocyte labeling with ¹¹¹In only under critically defined conditions.