Figure 3 Organisation of the sympathetic innervation in gut associated lymphoid tissue (adapted from Felten and colleagues²²). Noradrenergic fibres enter the serosal surface (S) pass through the muscle layers (ME, muscularis externa; MI, muscularis interna) and touch the myenteric plexus (MP), form a mesh of sympathetic nerve fibres (SMF) at the submucosal (SM) border of the MI, and then turn radially to run between lymph nodes (N) as internodular nerve fibres (INF). Fibres pass through the T dependent zone (T) and enter the interdomal region (ID) between the domes (D) and then branch profusely in this zone among lymphocytes, enterochromaffin cells, and subepithelial plasma cells. BV, blood vessel; SMP, submucosal plexus.