Direct Expression of the Extracellular Portion of Human FcεRIα Chain as Inclusion Bodies in Escherichia coli

Measurement for canine IgE using canine recombinant high affinity IgE receptor α chain (FcεRIα)

To detect allergen-specific IgE in dogs with allergic diseases, we developed a recombinant canine high affinity IgE receptor α chain (FcεRIα)-based IgE detection system. Using the recombinant protein of canine FcεRIα expressed by an Escherichia coli expression system, we could detect house dust mite (Dermatophagoides farinae) allergen-specific IgE in sera from dogs naturally and experimentally sensitized to this allergen with ELISA and western blotting. The IgE binding activity of recombinant canine FcεRIα on ELISA was impaired by heat treatment of these sera. The specificity of this recombinant canine FcεRIα-based IgE detection system was confirmed by inhibition assays with canine IgE. The recombinant canine FcεRIα-based IgE detection system established in this study offers an alternative tool to measure allergen-specific IgE in dogs.

Rapid receptor-proximal signaling assays for FcR gamma-containing receptors

Novel, cell-based assays, based on bioluminescence resonance energy transfer, have been developed for FcepsilonRI- and GPVI-FcRgamma complex-mediated signaling at receptor-proximal steps. In a stable transfectant of the HEK-293 cell line expressing human FcepsilonRIalpha, FcepsilonRIbeta, and FcRgamma-GFP2 and Syk(1-265)-Rluc fusion proteins, FcepsilonRI cross-linking markedly increased BRET2 ratios, which are the ratios of GFP2 emission to Rluc emission. These ratios reflect the FcRgamma-GFP2-Syk(1-265)-Rluc interaction in living cells. The signals are specifically inhibited by the Src-family kinase inhibitor PP2. Separately, in transient transfectants expressing GPVI, FcRgamma-GFP2, and Syk(1-265)-Rluc, the GPVI-specific ligand convulxin induced a two-fold increase in the BRET2 ratio and this increase was also inhibited by PP2. Finally, a differential assay was developed which permits the measurement of FcepsilonRI- and GPVI-FcRgamma complex-mediated signaling in the same cell. These assays provide useful methods for monitoring FcRgamma-Syk interaction in real time in living cells and may contribute to the understanding of signal regulation through FcRgamma-containing receptors.

Production of humanized antibody against human high-affinity IgE receptor in a serum-free culture of CHO cells, and purification of the Fab fragments

We describe the preparation of Fab fragments of a humanized anti-human high-affinity IgE receptor (Fc epsilonRIalpha) antibody potentially useful for treatment of IgE-mediated allergic diseases. IgE-binding capacities of sixteen combinations of light and heavy chains of four recombinant anti-Fc epsilonRIalpha antibodies, chimeric CRA2, humanized CRA2, chimeric CRA4, and humanized CRA4, were compared. A combination in which both chains were of humanized CRA2 had the highest activity. Stable transfectant clones of four kinds of host cells expressing recombinant antibodies were established. CHO-K1 cells were the most productive. Serum-free media suitable for culture of the stable CHO-transfectant clones were screened. The concentration of the humanized CRA2, which the most productive clone secreted into the chosen serum-free medium, was approximately 100 microg/ml. A procedure for the purification of the antibody, papain-digestion, and purification of Fab fragments was established. The highly purified humanized Fab fragments are suitable for use to examine their in vivo activity and immunogenicity in primates.