Background: CD26 is a multifunctional cell surface glycoprotein expressed by T and B cells. It exhibits a dipeptidyl-peptidase activity (DPP-IV) that cleaves the penultimate proline from the N-terminus of polypeptides, thereby regulating their activity and concentration.
Methods: Using CD26-/- mice resulting from targeted inactivation of the gene, we examined the consequences of a DPP-IV defect on behavioural response to nociceptive stimuli and concentration of the pain modulator peptides substance P (SP) and endomorphin 2, two DPP-IV substrates.
Results: CD26 inactivation induced a three-fold decrease in circulating endopeptidase activity while that found in brain extracts was normal, albeit very weak. CD26-/- mice had high SP concentrations in plasma (3.4+/-1 pg/ml versus 1.5+/-0.3 pg/ml, P<10(-3)) but not in brain extracts (35+/-12 pg/ml versus 32+/-9 pg/ml, P>0.05). Endomorphin-2 levels in the two groups were in the same range for plasma and brain extracts. CD26-/- mice displayed short latencies to nociceptive stimuli (hot plate test: 6.6+/-1.2 s versus 8.6+/-1.5 s, P<10(-4); tail pinch test: 3.1+/-0.6 s versus 4.2+/-0.8 s, P<10(-3)). Administration of an SP (NK1) receptor antagonist or DPP-IV to CD26-/- mice normalised latencies. DPP-IV inhibitors decreased latencies only in CD26+/+ mice.
Conclusions: Our observations represent the first fundamental evidence showing that DPP-IV influences pain perception via modulation of the peripheral SP concentration. Our work also highlights the role of peripheral NK1 receptors in nociception.