PLASTICITY OF INNERVATION OF THE MEDULLA OF AXILLARY LYMPH-NODES IN THE RAT AFTER ANTIGENIC-STIMULATION

The purpose of this investigation was to test the hypothesis that acti vation of the immune system in rats will lead to changes in the densit y of innervation in lymph nodes. In order to reduce the variability be tween animals, the rats were reared under sterile conditions and immun ostimulation was effected by subcutaneous application of bovine albumi n in a region draining to the axillary lymph nodes of both sides. Cont rol animals received an equivalent application of sterile physiologica l saline. The animals were sacrificed 10 days and 27 days and 4 months after immunostimulation. The nerves in the axillary lymph nodes were quantified by light microscopy in silver impregnated sections and at t he ultrastructural level on ultrathin sections. The survival times wer e chosen so that the first group was in the ascending phase of antibod y production, the second group at the peak, and the third group in the declining phase. Both at the light and ultrastructural levels, there were statistically significant differences in the density of innervati on of medulla between the groups, with a particularly pronounced incre ase in the group 4 months after immunostimulation. At the ultrastructu ral level, there was also an increase in the density of incompletely e nsheathed axonal profiles in the parenchyma of the medulla, while the nerves associated with blood vessels were not increased, We conclude t hat immunostimulation leads to morphological changes in the innervatio n of the medulla of axillary lymph nodes, that are consistent with the concept of functional activation of the autonomic nervous system thro ugh the immune system. (C) 1994 Wiley-Liss, Inc.