Contribution of dipeptidyl peptidase IV-sensitive neuropeptides to the control of inflammation in rheumatoid arthritis. Gray arrows indicate release of indicated mediator; black arrows indicate stimulation of indicated cell function; dashed lines indicate abrogation of cell function and/or release of indicated mediator. 'Endogenous opioids' include enkephalins, endorphins, dynorphin and endomorphin. CGRP, calcitonin gene-related peptide; IL, interleukin; NPY, neuropeptide Y; PGE2, prostaglandin E2; RO2-, reactive oxygen species; SP, substance P; TNF, tumor necrosis factor; VIP, vasoactive intestinal peptide.