Expression of delta opioid receptors by splenocytes from SEB-treated mice and effects on phosphorylation of MAP kinase

Delta opioid receptors (DORs) are known to modulate multiple T-cell respons es. However, little is known about the expression of these receptors. These studies evaluated the expression of DOR mRNA and protein after a single in vivo exposure to staphylococcal enterotoxin B (SEE). SEE (20 mug, ip) sign ificantly enhanced splenocyte DOR mRNA expression 8 and 24 h after injectio n. SEE also increased the fractions of the total splenocyte (5 to 20%) and T-cell (8 to 50%) populations expressing DOR protein. In saline-treated ani mals, DOR relative fluorescence intensity per cell was 11.1 +/- 0.62 units (mean +/- SEM), increasing to 16.1 +/- 1.7 after exposure to SEE. DOR fluor escence intensity significantly increased to 33.5 +/- 2.0 units in a subpop ulation of T-cells. Thus, SEE significantly increased DOR expression in viv o, affecting both mRNA and protein levels primarily within the T-cell popul ation. To determine whether T-cell DORs modulate the activity of extracellu lar-regulated kinases (ERKs), the phosphorylation of ERKs 1 and 2 was studi ed using splenocytes from SEE-treated mice. At concentrations from 10(-8) t o 10(-6) M, [D-Ala(2)-D-Leu(5)]-enkephalin, a selective DOR agonist, signif icantly inhibited anti-CD3-epsilon -induced phosphorylation of the ERKs. Th erefore, the DORs expressed by activated T-cells are capable of attenuating T-cell activation that depends on ERK phosphorylation. (C) 2000 Academic P ress.