The sympathetic nervous system mechanism of exendin-4 in respect of modulating T cell- mediated immune response to severe burns in mice

Abstract

Objective To investigate the potential effect of glucagon-like peptide-1 (GLP-1) analogue exendin-4 (Ex-4) on immune function of T lymphocytes via neuroendocrine modulation mechanism in mice following severe burns. Methods Male BALB/C mice were randomly(ramdam number) divided into thermal injury group (n=50) and sham-thermal group (n=30). The thermal injury model was made by exposing the back skin of 15% total body surface area (TBSA) to 95 ℃ water for 7 seconds, while in sham-thermal model the mice were immersed in 37 ℃ water instead. The expression of GLP-1 receptor (GLP-1R) was determined in sorted CD4+ T cells from normal mice by immunofluorescence method. In ex vivo experiment, the mice were sacrificed at 24 h post-burn, then the mononuclear cells (MNC) from spleen were separated from both groups and cultured in RMPI 1640 with 10%FCS (fetal calf serum) in presence of ConA (concanavalin A, 5 μg/mL). Cells were pretreated with catecholamine receptor antagonist propranolol (prop) for 1 hour, followed by consecutive dose of Ex-4 for another 48 h. In in vivo experiment, prop (30 mg/kg) was i. p. injected 30 minutes before thermal injury, then Ex-4 (2.4 nmol/kg) was injected i. p. immediately after scalding. Mice were sacrificed at 6 h and 24 h after thermal injury, then the serum and the spleens were collected. Results GLP-1R was expressed on splenic CD4+ T cells from normal mice. Ex-4 exerted no marked effect on the functions of T cells in terms of proliferation and IL-2 secretion at all doses examined ex vivo, which was not affected by pretreatment with prop. In vivo, T cell functions were suppressed by Ex-4 in thermal mice (P<0.05), but was restored by pretreatment with prop. Regardless of ex vivo or in vivo, Ex-4 could induce T cells switched to Th2 response (P<0.05). Moreover, the Th2 switch by Ex-4 was greatly potentiated by prop intervention in thermal mice in vivo other than ex vivo. Norepinephrine level was increased and epinephrine was decreased by Ex-4 in thermal mice. Both norepinephrine and epinephrine levels were obviously enhanced by pretreatment with prop. Conclusions Ex-4 can inhibit the proliferation and IL-2 secretion of splenic T lymphocytes through the sympathetic nervous system, however, it might induce Th2 switch from Th cells by acting directly on GLP-1R. Key words: Burn injury; Glucagon-like peptide-1; T lymphocyte; Immune response; Sympathetic nervous system