IgE antibodies to recombinant forms of Fel d I: dichotomy between fluid-phase and solid-phase binding studies.
BACKGROUND
The major cat allergen Fel d I consists of two polypeptide chains linked by disulfide bonds, each of which has been expressed in bacteria. To investigate the antigenic structure of Fel d I, antibody binding to the native molecule and to each recombinant chain were compared.


METHODS
Polyclonal human IgE and IgG antibodies and monoclonal antibodies (mAbs) to Fel d I were compared for binding to Fel d I, chain 1, or chain 2 by fluid-phase inhibition radioimmunoassay, RAST, and immunoabsorption.


RESULTS
In the fluid-phase assay, neither recombinant chain significantly inhibited the binding of antibody to native Fel d I at concentrations of up to 10 micrograms/ml. Partial inhibition was observed when chain 1 was used, which inhibited the binding of two mAbs by 40% and 75%. In contrast, when the solid-phase RAST assay was used, IgE antibodies bound both chains with high specificity, and there was a good quantitative correlation between IgE antibody binding to Fel d I and both chain 1 (r = 0.58, p < 0.01) and chain 2 (r = 0.47, p < 0.01). Up to 70% of IgG or IgE anti-Fel d I antibodies could be absorbed by either chain 1 or chain 2, and both chains in combination produced similar absorption values in response to native Fel d I. Four mAbs were fully absorbed by chain 1, but not chain 2, and three mAbs were not absorbed by either chain.


CONCLUSIONS
The results demonstrate a dichotomy between antibody binding to recombinant Fel d I chains, which may be explained by confirmational differences between the chains in the fluid phase or on solid supports. The results also suggest that chain 1 is an important site for mAb-defined B-cell epitopes on Fel d I.
Slunt
J B
JB
Department of Medicine, University of Virginia, Charlottesville 22908, USA.
Rogers
B L
BL
Chapman
M D
MD
D006023:Glycoproteins / Q000276:immunology*; D006801:Humans; D007073:Immunoglobulin E / Q000276:immunology*; D007163:Immunosorbent Techniques; D011852:Radioallergosorbent Test; D011994:Recombinant Proteins / Q000276:immunology
D006023:Glycoproteins; D011994:Recombinant Proteins; D007073:Immunoglobulin E; C059296:Fel d 1 protein, Felis domesticus