Further study on the roles of the effector molecules of immunosuppressive macrophages induced by mycobacterial infection in expression of their suppressor function against mitogen‐stimulated T cell proliferation
Previously, we found that phospholipids and reactive nitrogen intermediates (RNI) collaborated in expression of the T cell mitogenesis‐inhibitory activity of immunosuppressive macrophages induced by Mycobacterium avium‐intracellulare complex (MAIC) infection. In this study, we examined the roles of free fatty acids (FFA) and prostaglandins (PG) as effectors of MAIC‐induced macrophages, and moreover, their collaborating effects with RNI. First, treatment of MAIC‐induced macrophages with quinacrine (phospholipase A2 (PLA2) inhibitor), dexamethasone (inhibitor of PLA2 and PG synthesis) or indomethacin (PG synthesis inhibitor) attenuated their suppressor activity against concanavalin A (Con A)‐induced mitogenesis of splenocytes (SPC), indicating important roles of FFA liberated from membrane phospholipids and PG, as effectors. Second, oleic acid, PGE2, RNI generated from NOR 4 (a new nitric oxide (NO) donor), and phosphatidylserine (PS) exhibited suppressor activity against SPC mitogenesis without showing significant cytotoxicity, in an irreversible manner. Third, the suppressor activities of RNI and PGE2 were potentiated by combined use with oleic acid in a synergistic manner. Fourth, a dual‐chamber experiment in which target SPC were separated from MAIC‐induced macrophages by a Millipore filter revealed a requirement for cell‐to‐cell contact for expression of the suppressor function of MAIC‐induced macrophages. These findings indicate that RNI, FFA, PG, and phospholipids (presumably PS) and their collaboration play central roles in expression of the T cell mitogenesis‐inhibitory function of MAIC‐induced suppressor macrophages.