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Mutant derivatives of the main respiratory allergen of cow are less allergenic than the intact molecule

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Abstract:

Background

Allergen immunotherapy offers an alternative for drug treatment in the management of allergic diseases. Because immunotherapy often induces side-effects, less allergenic preparations would be beneficial. Objective

The purpose of this study was to examine whether the allergenicity of a cow-derived lipocalin allergen, Bos d 2, could be diminished by substituting or deleting carboxy-terminal amino acids including the cysteine which forms a disulphide bond with a cysteine inside the molecule. Methods

Four recombinant mutants of Bos d 2 were created by substituting or deleting the four most carboxy-terminal amino acids. The immunological characteristics of the mutant preparations were compared with the unmodified rBos d 2 by Western blotting, ELISA inhibition, skin prick tests, and the proliferative responses of allergen-specific T-cell clones. Results

In Western blot, one of the two monoclonal antibodies showed reduced binding to the preparations without the terminal cysteine. In contrast, the other monoclonal antibody, human IgE and rabbit immune serum bound equally well to all the preparations. ELISA inhibition analyses revealed, however, that the preparations without the terminal cysteine bound antibody less efficiently. They were needed 15–38 times more than the unmodified rBos d 2 to cause the same level of inhibition. Surprisingly, one of the mutants with the terminal cysteine but a mutated adjacent amino acid turned out to be the weakest in inducing skin reactivity. All the preparations stimulated well allergen-specific T-cell clones. Conclusions

The results show that the allergenicity of a lipocalin allergen, Bos d 2, can be diminished by modifying the carboxy-terminal end of the molecule. Modifications in the area which encompasses a disulphide bond impaired the antibody binding without affecting the T-cell stimulatory capacity. It was also shown that in vivo tests are necessary for determining the allergenicity of a modified allergen.

Keywords: allergic asthma; cow; disulphide bond; immunotherapy; recombinant allergen; site-directed mutagenesis

Document Type: Research Article

DOI: http://dx.doi.org/10.1046/j.1365-2222.1999.00605.x

Affiliations: 1: Department of Clinical Microbiology, University of Kuopio, 2: Department of Pulmonary Diseases, Kuopio University Hospital, Kuopio, Finland

Publication date: July 1, 1999

bsc/cea/1999/00000029/00000007/art00017
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