Figure 1.A simplified scheme of the bi-directional communication between the brain and the immune system; role of central and peripheral neuroendocrine and immune adaptive responses triggered by an immune challenge (see text). Lymphoid organs, and particularly their parenchyma, similar to smooth muscles of the vasculature, receive predominantly sympathetic/noradrenergic and sympathetic/neuropeptides Y, and peptidergic/sensory innervation; the heart and the gastrointestinal tract receive both sympathetic and parasympathetic (cholinergic) innervation.Abbreviations: Ab, antibody; CNS, central nervous system; CRP, C-reactive protein; HPA, hypothalamic-pituitary-adrenal (axis); IL, interleukin, Ly, lymphocyte; SNS, sympathetic nervous/adrenomedullary system; Th, T helper cell (response); TNF, tumor necrosis factor.