CD1-dependent natural killer (NK1.1⁺) T cells are required for oral and portal venous tolerance induction

Background. Local antigen presentation via either the oral (PO) or the portal venous (PV) routes results in suppression of systemic delayed-type hypersensitivity (DTH). The responsible cell populations are not well defined. Because NK1.1⁺ T cells express the Fas ligand and produce high levels of the immunosuppressive cytokine, IL-4, they may play a role in both activated T-cell apoptosis and a Th1 to Th2 immune shift, thus promoting tolerance induction. Methods. C57BL/6 mice were tolerized to BALB/c alloantigen by PV or PO spleen cells (25 × 10⁶) on Day 0. Subcutaneous (SQ) challenge with 10 × 10⁶ BALB/c cells on Day 7 was followed by footpad injection of 10 × 10⁶ BALB/c cells on Day 14. Footpad swelling was measured 24 h later. A single injection of the NK1.1⁺ cell-depleting antibody, PK-136, was given IP (10 mg/kg) 2 days prior to PV or PO antigen. Flow cytometry evaluated NK1.1⁺ cell depletion. CD1 knockout (KO) mice, lacking NK1.1⁺ T cells, were also challenged with PV and PO Balb/c in parallel experiments. Results. The DTH to BALB/c antigen was markedly suppressed in C57BL/6 mice when this alloantigen was given by either PO or PV routes (P < 0.001, P < 0.001). The maintenance of an unaltered response to third-party C3H/HeJ demonstrated alloantigenic specificity. Administration of the anti-NK1.1 T cell monoclonal antibody, PK-136, resulted in complete restoration of in vivo DTH responsiveness in PO tolerance (P < 0.01), and partial restoration in PV tolerance (P < 0.05) in C57BL/6 mice. FACS confirmed virtually complete depletion of liver, splenic, Peyer's patch, and mesenteric lymph node NK1.1⁺ lymphocytes. Development of both PO and PV tolerance was prevented in CD1 KO mice. Conclusion. NK1.1⁺ T cells play an essential role in antigen-specific suppression of the DTH response mediated by both oral and portal venous tolerance.