Adrenergic regulation of macrophage-derived tumor necrosis factor-α generation during a chronic polyarthritis pain model

Increases in the levels of proinflammatory cytokines, such as TNFα, have been intricately linked with arthritis and the pathogenesis of several models of neuropathic pain. In addition, arthritis (as well as other types of persistent pain) is associated with increased sympathetic activity and alterations of other responses in autonomic nervous activity. Adrenergic regulation of LPS-stimulated TNF production by Mφ isolated from rats with streptococcal-cell-wall (SCW)-induced arthritis has been examined. Serum TNF levels and the cellular composition of peritoneal exudates have also been assessed. Mφ were obtained from: (1) normal control rats, (2) animals injected with complete Freund's adjuvant (CFA), (3) rats injected with SCW and arthritic, and (4) those injected with SCW, which failed to develop arthritis. Serum levels of TNFα in rats that develop arthritis are significantly greater (2.4 fold) than levels from the other groups. The proportion of OX19-positive T cell subpopulations are the same in peritoneal exudates from all groups. Immunocytochemical staining also reveals differences between Mφ subgroups in the degree of activation. Peritoneal exudates from rats that develop arthritis contain a greater proportion of the high TNF producing subclass of Mφ, as identified by positive ED3 staining (p < 0.001). In contrast, Ia antigen presenting Mφ (OX6-positive) in the peritoneal exudate cells are only elevated in rats administered CFA. The selective blockade of adrenergic receptors by idazoxan or propranolol demonstrates that the constitutive involvement of either α₂ or β- adrenergic regulation of Mφ-derived TNF production is pronounced in rats with arthritis (p < 0.001). These investigations demonstrate a distinctive pattern of peripheral Mφ populations in rats that develop chronic polyarthritic pain. We believe that identification of interactions between the adrenergic responses and proinflammatory cytokines will lead to the development of improved strategies to treat patients with chronic pain.