Transgenic mice expressing the human high-affinity immunoglobulin (Ig) E receptor alpha chain respond to human IgE in mast cell degranulation and in allergic reactions.

The high-affinity receptor for immunoglobulin (Ig) E (Fc epsilon RI) on mast cells and basophils plays a key role in IgE-mediated allergies. Fc epsilon RI is composed of one alpha, one beta, and two gamma chains, which are all required for cell surface expression of Fc epsilon RI, but only the alpha chain is involved in the binding to IgE. Fc epsilon RI-IgE interaction is highly species specific, and rodent Fc epsilon RI does not bind human IgE. To obtain a "humanized" animal model that responds to human IgE in allergic reactions, transgenic mice expressing the human Fc epsilon RI alpha chain were generated. The human Fc epsilon RI alpha chain gene with a 1.3-kb promoter region as a transgene was found to be sufficient for mast cell-specific transcription. Cell surface expression of the human Fc epsilon RI alpha chain was indicated by the specific binding of human IgE to mast cells from transgenic mice in flow cytometric analyses. Expression of the transgenic Fc epsilon RI on bone marrow-derived mast cells was 4.7 x 10(4)/cell, and the human IgE-binding affinity was Kd = 6.4 nM in receptor-binding studies using 125I-IgE. The transgenic human Fc epsilon RI alpha chain was complexed with the mouse beta and gamma chains in immunoprecipitation studies. Cross-linking of the transgenic Fc epsilon RI with human IgE and antigens led to mast cell activation as indicated by enhanced tyrosine phosphorylation of the Fc epsilon RI beta and gamma chains and other cellular proteins. Mast cell degranulation in transgenic mice could be triggered by human IgE and antigens, as demonstrated by beta-hexosaminidase release in vitro and passive cutaneous anaphylaxis in vivo. The results demonstrate that the human Fc epsilon RI alpha chain alone not only confers the specificity in human IgE binding, but also can reconstitute a functional receptor by coupling with the mouse beta and gamma chains to trigger mast cell activation and degranulation in a whole animal system. These transgenic mice "humanized" in IgE-mediated allergies may be valuable for development of therapeutic agents that target the binding of IgE to its receptor.

Tepoxalin, a novel immunomodulatory compound, synergizes with CsA in suppression of graft-versus-host reaction and allogeneic skin graft rejection.

Tepoxalin, a dual 5-lipoxygenase and cyclooxygenase inhibitor with nonsteroidal antiinflammatory effects, has recently been shown to suppress NF kappa B transactivation and inhibit T cell proliferation via a mechanism very different from cyclosporine (CsA). In this report, we demonstrate that this novel immunosuppressive effect of tepoxalin is manifested in in vivo transplantation models. Tepoxalin suppressed murine spleen cell proliferation in a mixed lymphocyte reaction (MLR) with an IC50 of 1.3 microM. Coadministration of tepoxalin and CsA in MLR cultures showed an additive inhibitory effect. Oral administration of tepoxalin at 12 mg/kg/day to mice suppressed local graft-versus-host (GVH) responses by about 40% (n = 10). Combination of tepoxalin and CsA at suboptimal doses synergized their immunosuppressive effects on GVH responses (n = 20). In skin transplantation, the median survival time of allogeneic BALB/cByJ (H-2d) mouse skin grafted onto C3H/HeJ (H-2 kappa) mice was 10.5 days (n = 8), and was prolonged to 15.0 days (n = 9) for recipient mice administered tepoxalin at 50 mg/kg/day. Coadministration of suboptimal doses of tepoxalin (12.5 mg/kg/day) and CsA (50 mg/kg/day) prolonged skin graft rejections dramatically (55% of the grafts survived for more than 40 days, n = 9). Taken together, these results demonstrate that tepoxalin is a potent immunomodulatory compound that, when combined with CsA, provides synergistic immunosuppressive activity. The fact that tepoxalin and CsA act on different transcription factors, NF kappa B and NFAT respectively, might explain the synergistic suppressive effects when both compounds were used. Tepoxalin could be an important addition to the cohort of immunosuppressive therapies currently used in solid organ and bone marrow transplantations.