Delta opioid receptors (DORs) modulate a myriad of immune functions such as T cell proliferation, IL-2 production and chemokine- mediated chemotaxis. Recently, delta opiate agonists have been reported to inhibit the expression of HIV- l p24 antigen by a DOR- transfected T cell line (DOR-Ju. 1). The inducible expression of enkephalins by thymic and splenic lymphocytes strongly suggests that the modulation of T cells by DORs is physiological. Although several laboratories have detected DOR mRNA in mononuclear cells from rodents and primates, little is known about the regulated expression of DOR mRNA. These investigations will evaluate its induction in vitro by cross-linking the T cell receptor (TCR) in the presence and absence of anti-CD28 costimulation. The phenotype(s) of the lymphocytes expressing DOR mRNA and the effects of activated protein kinase C on the induction of DOR in unstimulated cultures and through the TCR will be determined. Additional studies will focus on the induction of DOR mRNA in vivo, using the naturally occurring superantigen, staphylococcal enterotoxin B (SEB). The intracellular signals mediating the immunomodulatory effects of DORs have not been identified. Although the mitogen activated protein kinases (MAPKs), ERKs l, 2, are activated by the DORs in DOR-Ju,l cells, DOR agonists suppress the TCR-dependent phosphorylation and activation of ERKs in splenic T cells.
In specific aim #2, the role of phosphatases (e.g. SHP-1, - 2, MKP 1-3, PAC-1) in the suppression of ERK l, 2 phosphorylation by DORs will be evaluated by characterizing the effects of DOR agonists on the expression, phosphorylation and activity of T cell phosphatases. Additional studies will assess the effects of DORs on early events required for the TCR-dependent activation of ERKs l, 2, such as the phosphorylation of key subunits of the TCR complex (e.g. CD3-zeta).
Specific aim #3 will address the clinical significance of DOR-dependent immunomodulation in human peripheral blood CD4+ T cells by continuing our studies of HIV-l expression. In pharmacological studies, the effects of two DOR agonists, SNC-80 and DADLE, on HIV-l p24 antigen expression by normal CD4+ T cells infected with primary isolates of HIV-l will be compared to the Minnesota strain. Mechanistic studies will correlate the efficacy of these agonists with the expression of DOR mRNA by activated human CD4+ T cells. The binding activity of nuclear factor kappaB, which is involved in transactivation of HIV-l replication, and the expression and phosphorylation of the chemokine receptors CXCR4 and CCR5, which are co-receptors for HIV-l uptake, will also be evaluated. In summary, these investigations will help clarify our understanding of the expression and function of T cell DORs and their potential immunopharmacological role in modulating the T cell response to HIV- 1.
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