T cells affect central and peripheral noradrenergic mechanisms and neurotrophin concentration in the spleen and hypothalamus.

Interactions between T cells and noradrenergic pathways were investigated using athymic nude mice as a model. Higher noradrenaline (NA) concentrations and increased density of noradrenergic fibers were found in the spleen and hypothalamus, but not in the kidney, of 21-day-old Foxn1(n) (athymic) mice, compared with Foxn1(n) /Foxn1(+) (heterozygous) littermates. Although no differences in nerve growth factor concentrations were detected, significantly higher brain-derived neurotrophic factor concentrations were found in the spleen and hypothalamus of athymic mice compared with the controls. All of these alterations were abrogated in Foxn1(n) mice reconstituted by thymus transplantation at birth. These results suggest that T lymphocytes or their products can induce (1) a decrease in the number and activity in splenic sympathetic nerve fibers; (2) a decrease in NA content in the hypothalamus, which, in turn, may influence the pituitary-adrenal axis and the descending neural pathways associated with the autonomic nervous system; and (3) changes in neurotrophin concentration in the spleen and hypothalamus.