Chemiluminescence and immune cell activation. II. Enhancement of concanavalin A-induced chemiluminescence following in vitro preincubation of rat thymocytes; dependency on macrophage-lymphocyte interaction.

The immediate chemiluminescence (CL) response to concanavalin A (Con A) of rat thymocytes is enhanced 10 to 20-fold when the cells are preincubated in serum-free medium for 5--20 h. During this period, multiple encounters between lymphocytes and macrophages occur which morphologically appear as rosettes or grape-like cell aggregates. Additionof bone marrow-derived macrophages increases the number of cell aggregates and also the CTL response to Con A. Paradoxically, removal of macrophage-containing cell aggregates after cocultivation leaves a pure thymocyte population which strongly responds to Con A with CL. Our results confirm that macrophage-depleted "competent" lymphocytes are capable of CL and, furthermore, that "competence" is gained during cocultivation with macrophages. We are therefore convinced that measurements of macrophage and lymphocyte CL are a powerful tool for further elucidation of lymphocyte differentiation and of interactions between macrophages and lymphocytes.