Neuropeptide denervation alters both the elicitation and induction phases of contact hypersensitivity in mice

The effects of permanent disruption of neuropeptide transmission on the ind uction (i.e., sensitization) and elicitation (i.e., challenge) phases of co ntact hypersensitivity (CHS) are described. BALB/c mice were chemically den ervated of neuropeptide (i.e., tachykinin) containing sensory C fibers by a n acute injection of capsaicin (50 mg/kg) on postnatal day (PND) 2 to 3. As young adults (PND 45-60), these mice and their control littermates were se nsitized by topical application of 0.1% 2,4-dinitrofluorobenzene (DNFB) or vehicle. Treatment groups generated from this exposure regimen consisted of untreated, controls (O/O), denervated, controls (CAP/O), untreated, sensit ized (O/DNFB), and denervated, sensitized (CAP/DNFB). The elicitation phase of CHS was evaluated in these animals by measuring ear thickness in respon se to a DNFB challenge. In DNFB-sensitized groups, ear thickness was signif icantly increased over controls but was additionally increased 2.4-fold in CAP/DNFB compared to O/DNFB mice. The induction phase of CHS was next asses sed in young adult mice by measuring lymph node cell (LNC) proliferation. F or this, mice were sensitized for 3 consecutive days before their draining, auricular nodes were removed. The LNC were dissociated and cultured for 24 h with tritiated thymidine to assess LNC proliferation. As expected, signi ficantly higher numbers of LNC occurred in both DNFB-sensitized groups (CAP /DNFB, O/DNFB) compared to the unsensitized, controls (CAP/O, O/O). However , LNC proliferation in CAP/DNFB was significantly higher than O/DNFB animal s. Flow cytometry on similarly exposed mice failed to demonstrate any signi ficant difference in the population of CD4CD8 or CD3CD45R LNC cells from ne uropeptide-denervated (CAP/O, CAP/DNFB) mice or their respective treatment mates (O/O, O/DNFB), suggesting that alterations in T or B cell populations did not underlie these changes. Finally, cytokine release from the LNC fro m these treatment groups was examined. For this, the auricular lymph nodes were removed from animals, 2 to 4 h after the animals were administered a s ingle application of a sensitizing concentration (0.1%) of DNFB or acetone vehicle. LNC, dissociated from these nodes, were cultured for 24 h. The nut rient media was removed from these cultured cells and examined for the rele ase of proinflammatory cytokines, interleukin (IL)-1 beta, IL-2 and tumor n ecrosis factor (TNF)alpha, by ELISA. There were no significant increases in IL-2. However, IL-1 beta release was significantly increased in CAP/DNFB m ice over O/DNFB by 18-fold and by over 30-fold compare to O/O controls. Lev els of TNF alpha were significantly increased in both O/DNFB and CAP/DNFB m ice over the nonsensitized controls (O/O, CAP/O). CAP/DNFB values were appr oximately double that of O/DNFB. There was no significant difference in IL- 1 beta or TNF alpha release between the nonsensitized controls (O/O, CAP/O) . Collectively, these data indicate that neuropeptide denervation by neonat al administration of capsaicin alters both the induction and elicitation ph ases CHS and may modify sensitivity to chemically induced CHS.