Estrogen modulates neural–immune interactions through intracellular signaling pathways and antioxidant enzyme activity in the spleen of middle-aged ovariectomized female rats

• Estrogen reverses ovariectomized-induced reduction in T cell immune responses
• Estrogen enhances splenic p-TH and NGF expression and intracellular signaling markers
• Estrogen augments lipid peroxidation, and protein carbonyl formation in the spleen

Modulation of neural–immune interactions by estrogen in the spleens of ovariectomized (OVX) middle-aged female rats was examined. Con A-induced lymphoproliferation, splenic tyrosine hydroxylase (TH) and nerve growth factor (NGF) expression, levels of p-ERK 1/2, p-CREB, and p-Akt, and activity of superoxide dismutase decreased in OVX rats while estrogen treatment enhanced their expression, levels, and activity. Also, estrogen treatment enhanced Con A-induced IFN-γ production and decreased Con A-induced IL-2 production compared to OVX animals. In contrast, estrogen increased the extent of lipid peroxidation and protein carbonyl formation while OVX induced a decline in protein carbonyl formation. These results suggest that estrogen enhances neural–immune interactions while simultaneously affecting it through generation of free radicals as reflected by increased lipid peroxidation and protein carbonyl formation.