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

Abstract

SUMMARYPreviously, 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 A 2 (PLA 2 ) inhibitor), dexamethasone (inhibitor of PLA 2 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, PGE 2 , 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 PGE 2 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.

Comparative studies on the roles of mediator molecules in expression of the suppressor activity ofMycobacterium aviumcomplex-induced immunosuppressive macrophages against T cell and B cell mitogenic responses

“…We previously found that the immunosuppressive signals of MAC-MΦs were transmitted to the target T cells via cell-tocell contact [13][14][15]. As shown in Fig.…”

“…We previously found that RNIs, free fatty acids (such as arachidonic acid), TGF-β, PGE 2 and phosphatidylserine inhibited T cell mitogenesis in a significant manner, thereby suggesting that these factors play roles as the suppressor mediators of MAC-MΦs [11][12][13]. Therefore, we next compared the susceptibilities of T cell and B cell mitogenesis to these suppressor mediators.…”

“…Culture supernatants of MAC-M Φ s with or without target normal SPCs were allowed to react with Griess reagents, and nitrite content was quantified by measuring absorption at 550 nm as previously described [13].…”

“…In order to understand the role of RNIs, important mediators of suppressor M Φs [12,13,21,25,26], in the expression MAC-MΦ's suppressor activity against B cell mitogenesis, we compared the effects of L-NMMA on the MAC-MΦ-mediated suppression of the proliferative responses of SPCs to Con A and LPS stimulation. As indicated in Fig.…”

“…MAC-M Φ s were found to strongly down-regulate IL-2 receptor expression by Con Astimulated T cells and moderately reduced the IL-2 production of the T cells [9,10]. It has also been found that the suppressor activity of MAC-M Φ s is mediated by humoral mediators, including reactive nitrogen intermediates (RNIs), transforming growth factor-β (TGF-β ), free fatty acids, phosphatidylserine and prostaglandin E 2 (PGE 2 ), which are produced by MAC-M Φ s responding to Con A stimulatory signals and some kinds of immunopotentiating cytokines, especially IFN-γ and TNF-α [11][12][13]. Recently, we have elucidated that the B7-1-like molecule-mediated cell contact of MAC-M Φ s with target T cells is required for the efficacious manifestation of MAC-M Φ 's suppressor activity [14] and that the MAC-M Φ -derived suppressor signals cross-talk with the early signalling events before the activation of protein kinase C and/or intracellular calcium mobilization [15].…”