Norepinephrine-Mediated Inhibition of Antitumor Cytotoxic T Lymphocyte Generation Involves a β-Adrenergic Receptor Mechanism and Decreased TNF-α Gene Expression

Abstract

We have previously shown that norepinephrine (NE) inhibits the in vitro generation of anti-MOPC-315 CTL activity by spleen cells from BALB/c mice rejecting a large MOPC-315 tumor as a consequence of low-dose melphalan (l-phenylalanine mustard (l-PAM)) treatment (l-PAM TuB spleen cells). Since TNF-α plays a key role in the generation of antitumor CTL activity in this system, we determined whether NE mediates this inhibition through inhibition of TNF-α production. Here, we show that NE inhibits the production of TNF-α protein and mRNA by l-PAM TuB spleen cells stimulated in vitro with mitomycin C-treated tumor cells. Flow cytometric analysis of intracellular expression of TNF-α revealed substantial NE-mediated decreases in the percentages of TNF-α+ cells among CD4+ and CD8+ T cells and F4/80+ activated macrophages. NE inhibition of CTL generation was largely overcome by addition of TNF-α to the stimulation cultures. When the β-adrenergic antagonist propranolol was added to the stimulation cultures of l-PAM TuB spleen cells at a concentration that prevented NE-induced cAMP elevation, the NE-mediated decrease in TNF-α mRNA and NE-mediated inhibition of CTL generation were reversed. Collectively, these results suggest that NE inhibits antitumor CTL generation, at least in part, by inhibiting TNF-α synthesis through a mechanism(s) involving β-adrenergic receptor signaling.