Differential effects of neuropeptide Y (NPY) on leukocyte subsets in the blood: mobilization of B-1-like B-lymphocytes and activated monocytes.

Sympathetic nervous system activation mobilizes leukocytes but it is unknown whether the concomitant neuropeptide Y (NPY)-release also alters blood leukocyte counts. Using chronic intravenous (i.v.) cannulation of freely moving rats and flow cytometry, time-, dose- and subset-specific effects of NPY on blood leukocytes were investigated 1-15 min after injection: High-dose NPY increases leukocytes numbers by preferentially mobilizing CD4(+) T-cells, activated NKR-P1A(+) monocytes and NK-cells. Low-dose NPY significantly decreases B-lymphocyte and NK-cell numbers. Furthermore, NPY dose-dependently mobilizes a previously undetected IgM(low)CD5(+)CD11b(+) B-cell subpopulation in rats ("B1-like" B-lymphocytes). These data suggest a role for the sympathetic neurotransmitter NPY in neuroimmune alterations in vivo.