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Further Characterization of the Alternative Protein‐A Interaction of Immunoglobulins: Demonstration of an Fc‐binding Fragment of Protein A Expressing the Alternative Reactivity
Author(s) -
INGANÄS M.,
JOHANSSON S. G. O.,
SJÖQUIST J.
Publication year - 1981
Publication title -
scandinavian journal of immunology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.934
H-Index - 88
eISSN - 1365-3083
pISSN - 0300-9475
DOI - 10.1111/j.1365-3083.1981.tb00578.x
Subject(s) - polyclonal antibodies , antibody , fragment crystallizable region , chemistry , microbiology and biotechnology , immunoglobulin fc fragments , immunoglobulin g , protein g , immunoglobulin e , protein a , protein a/g , biochemistry , biology , receptor , recombinant dna , immunology , gene , fusion protein
Intact IgG and fragments F(ab') 2 γ, Fabγ and Fcγ from a rabbit anti‐protein‐A serum (RapA) and corresponding preparations from normal rabbit IgG (NRG) were tested for their inhibitory effect on the binding of protein‐A‐reactive 125 I‐IgE and 125 I‐Fcγ, respectively, to protein‐A–Sepharose. Intact IgG, F(ab') 2 γ and Fabγ of RapA inhibited the binding of protein‐A‐reactive 125 I‐IgE, whereas only intact IgG and Fcγ fragments from both RapA and NRG inhibited the binding of 125 Fcγ to protein A‐Sepharose. Further, the functional relationship between RapA and human polyclonal IgG was studied in a nephelometric test system. Intat IgG or fragments of IgG from human polyclonal IgG and rabbit anti‐protein‐A were found to affect the precipitation between human IgG and protein A in a similar way. Thus F(ab') 2 γ fragments and intact IgG enhanced the precipitation, whereas Fabγ and Fcγ fragments inhibited the precipitation. Protein A and an Fc‐binding fragment of protein A (fragment B) were tested for their abilities to link different radiolabelled immunoglobulin preparations expressing the alternative and the classical protein‐A reactivity to immobilized Fc fragments. All proteins expressing the alternative reactivity were efficiently bound both by fragment B and by protein A, indicating that fragment B, in addition to its classical Fc‐binding activity, also expresses the alternative protein‐A reactivity.