Biological properties of a recombinant human immunoglobulin ε-chain fragment

A recombinant human immunoglobulin ε-chain gene expression product (rFc(ε)) was compared with a human E myeloma protein in the affinity for ε-chain Fc fragment receptors (Fc(ε)R) on cultured human basophils. The association-dissociation kinetics of the rFc(ε)-Fc(ε)R interaction are indistinguishable from that of E myeloma protein, indicating that rFc(ε) and IgE have identical affinity for the receptors. The recombinant gene product sensitizes cultured basophils for anti-IgE-induced histamine release. A dose-response curve of histamine release indicates that the gene product is equally efficient in transducing the signal for degranulation as the natural IgE. Both the rFc(ε) and IgE lost the affinity for Fc(ε)R by heating at 56°C. Upon renaturation by passage through a solution of 6 M guanidine hydrochloride, rFc(ε) recovered both the affinity for Fc(ε)R and the original CD spectra. On the other hand, renaturation of heat-denatured IgE largely restored optical activity above 250 nm but restored neither the affinity for Fc(ε)R nor the CD spectrum below 220 nm. The results suggest that either the amino acid sequence or the carbohydrate present in the myeloma protein, but not the rFc(ε), may interfere with refolding of the receptor-binding structures.