Nerve growth factor and cytokines mediate lymphoid tissue-induced neurite outgrowth from mouse superior cervical ganglia in vitro

Superior cervical ganglia (SCG) from neonatal mice were cultured with adult murine lymphoid tissue explants in Matrigel (Collaborative Biomedical, Bedford, MA). After 1 and 2 days in culture, many neurites grew toward thymus and spleen. Normal mesenteric lymph node (MLN) induced a smaller effect; however, activated MLN (isolated from mice 10 days after infection with Nippostrongylus brasiliensis; Nb-MLN-10d) caused significantly increased neurite outgrowth. To determine the roles of nerve growth factor (NGF) and cytokines in the promotion of neuritogenesis by lymphoid tissues, anti-NGF and various anti-cytokines were added to cocultures. Anti-NGF inhibited most of the neurite outgrowth toward thymus and spleen but only partially that toward Nb-MLN-10d. Anti-mouse IL-1 beta also significantly reduced the number of neurites growing toward thymus, spleen, and normal MLN. The number of neurites growing toward Nb-MLN-10d was significantly reduced by anti-IL-1 beta, anti-IL-3, anti-IL-6, or anti-GM-CSF. Exogenous IL-1 beta and IL-3 caused neurite outgrowth in single SCG cultures; and the IL-1 beta-, but not the IL-3-, mediated effect was completely blocked by anti-NGF. In one-day thymus/SCG cocultures, endogenous IL-1 was not detectable at concentrations sufficient to cause nerve growth; however, ample NGF was present in the thymic tissues and culture supernatants, but not in SCG. These data suggest that IL-1 mediates NGF production in lymphoid tissues, which in turn induces the growth of sympathetic nerves. Moreover, IL-3, IL-6, or GM-CSF produced during inflammation might also play important roles in the stimulation of nerve growth in vivo.