Noradrenergic and peptidergic innervation of secondary lymphoid organs: role in experimental rheumatoid arthritis

Noradrenergic (NA) and peptidergic nerve fibres are present in both primary and secondary lymphoid organs, distributing with the vasculature, trabecular and capsular smooth muscle, and within the parenchyma among cells of the immune system. NA nerve terminals directly abut lymphocytes and macrophages in spleen and lymph nodes. In these organs, norepinephrine has fulfilled the basic criteria for neurotransmission with cells of the immune system as targets. In vitro and in vivo studies have demonstrated NA modulation of primary and secondary antibody responses, cytotoxic T cell responses, natural killer cell activity, and proliferation and differentiation of both T and B lymphocytes. Substance P (SP) has been shown to modulate inflammatory responses, lymphocyte proliferation, and other immunologic reactivity. We investigated the role of NA and SP nerve fibres within lymph nodes in experimental allergic auto-immune arthritis in Lewis rats. Denervation of NA nerve fibres in popliteal and inguinal lymph nodes with 6-hydroxy-dopamine resulted in earlier onset and enhanced severity of arthritic changes as well as inflammation in bilaterally induced experimental arthritis, while denervation of SP nerve fibres in popliteal and inguinal lymph nodes with capsaicin resulted in delayed onset and diminished severity of the inflammatory changes ipsilaterally, and prevention of contralateral arthritic changes in unilaterally induced experimental arthritis. These findings suggest that NA and SP nerve fibres in lymph nodes can modulate the time course of onset and the severity of experimental arthritis in Lewis rats. These modulatory effects are distinctly different from the effects of NA and SP nerve fibres in the joints themselves.