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P032. Genetic deletion and pharmacological inhibition of chemokine receptor 9 (CCR9) result in opposite effects on the development of oral tolerance

M. Walters1, K. Ebsworth1, T. Sullivan1, J. Jaen1, T. Schall1

1Chemocentryx, Mountain View, United States

Background: Recently published data indicate that CCR9-deficient (CCR9−/−) mice display an impaired ability to generate oral tolerance. Given that different outcomes have been reported between pharmacological inhibition of CCR9 versus genetic deletion of CCR9 in the TNF‑ΔARE mouse model of ileitis, the ability of a CCR9 antagonist to impair the generation of tolerance towards oral antigens was tested.

Methods: Tolerance was induced in mice by daily oral administration of ovalbumin (OVA) for 5 days. Mice dosed with PBS (no OVA) were used as positive controls for absence of systemic tolerance. Daily treatment with a CCR9 antagonist was started prior to the initial oral antigen exposure and continued throughout the period of antigen dosing. Following exposure to the oral antigen, mice were immunized systemically with OVA:adjuvant on day 7. Oral tolerance was determined by delayed-type hypersensitivity (DTH) reaction induced by intra-dermal injection of OVA into the right ear, with the left ear serving as a control, 7 days after systemic OVA immunization. Ear thickness was measured with calipers 24 hours after challenge.

Results: Control mice receiving oral PBS (no OVA) displayed an OVA-specific DTH response (ear swelling: 0.084±0.009 mm). Mice that were exposed orally to OVA developed systemic tolerance, as determined by a significantly reduced OVA-specific DTH response (0.01±0.005 mm; P = 0.001 vs. no-OVA controls). Mice exposed orally to OVA and treated concurrently with a small-molecule CCR9 antagonist developed systemic tolerance that was indistinguishable from control animals not treated with the antagonist, as evidenced by a greatly diminished OVA-specific DTH response (0.006±0.002 mm; P ≤ 0.0001 vs. no-OVA controls). In contrast, CCR9−/− mice were resistant to oral tolerance induction and displayed DTH responses equivalent to PBS-treated (no OVA) wild-type mice (0.12±0.012 vs. 0.16±0.024 mm; NS).

Conclusions: The results presented here clearly demonstrate that pharmacological inhibition of CCR9 does not inhibit the generation of systemic tolerance to oral antigen. Genetic deletion of CCR9 does result in impairment of oral tolerance induction. These results add to earlier observations in other experimental settings which indicated that genetic deletion of CCR9 is not a sound model for predicting the outcome of pharmacological inhibition of CCR9.