The aim of this study was to elucidate the immunoregulatory role of the neuropeptide, nociceptin (N/OFQ). The effects on human peripheral blood mononuclear cells (PBMCs), CD4⁺ T cells, T regulatory (Treg) cells and dendritic cells (DCs) were investigated. N/OFQ (10⁻¹⁴M and 10⁻¹⁰M) suppressed the proliferative response of PBMCs to the superantigen, staphylococcal enterotoxin B (SEB) and 004⁺ T cells stimulated with CHO(DR4/SEB/CD80) (OHO cells transfected with DR4 and MHO class II and pulsed with SEB). N/OFQ-induced decreased proliferation of SEB-activated T cells, could be blocked by the putative N/OFQ antagonist, UFP-101, indicating the response is specific to N/OFQ. Expression of the co-stimulatory receptor, glucocorticoid-!nduced tumour necrosis factor receptor (GITR) decreased In response to N/OFQ (10⁻¹⁰M) and expression of CD80 increased in response to N/OFQ (10⁻¹⁴M). Functional studies revealed an inhibitory role for CD80 in modulating T cell proliferation. Moreover, CD80 and to a lesser extent, CD86 are involved in the suppressive effect mediated by N/OFQ. N/OFQ can therefore modulate T:T cell communication.EThOS - Electronic Theses Online ServiceGBUnited Kingdo