Lymph nodes--a possible site for sympathetic neuronal regulation of immune responses

Noradrenergic fibers were identified in rat cervical lymph nodes by fluorescence histochemistry and confirmed by radioenzymatic determination of norepinephrine. After superior cervical ganglionectomy, lymph node norepinephrine and noradrenergic fluorescence were strikingly decreased. The alpha-adrenergic radioligand [3H] dihydroergocryptine bound to saturable sites on lymph node membranes (0.20 pmol/mg protein; affinity constant, 8 nM) with characteristics expected for alpha-adrenergic receptor binding. The alpha-adrenergic binding sites were present in high concentration in membranes from lymph node stroma but were negligible in membranes of lymphocytes teased from nodes. In lymph nodes the ratio of alpha-adrenergic binding sites to norepinephrine content was higher than ratios of many other sympathetically innervated tissues such as iris or vas deferens. The presence of sympathetic innervation and the high concentration of alpha-adrenergic binding sites relative to that innervation suggest that the sympathetic nervous system modulates an intrinsic lymph node function through alpha-adrenergic mechanisms.