Non-immune IgG F(ab')2 binding to group C and G streptococci is mediated by structures on gamma chains.
The present investigation was designed to determine whether the heavy or the light immunoglobulin chain is involved in the non-immune binding of IgG F(ab')2 fragments to specific surface receptors on human group C and G streptococci. Purified human polyclonal IgG was mildly reduced with dithiothreitol and alkylated with iodoacetamide. Light (L) and heavy (H) chains were separated. Intact IgG and purified L and H chains of polyclonal immunoglobulin G were tested in an inhibition assay for non-immune IgG F(ab')2-mediated binding to group C and G streptococci. H chains inhibited the uptake of isotope-labelled IgG F(ab')2 fragments. Isolated L chains were non-reactive. Intact IgG molecules were more potent inhibitors than isolated H chains tested in equimolar concentrations. These results indicate that the non-immune interaction between human group C and G streptococci and F(ab')2 fragments of human IgG is mediated by reactive sites exposed on the immunoglobulin G H chains. The observation that intact IgG on a molar basis was more inhibitory than purified gamma chains suggests that the L chains may contribute to the reactivity, presumably by passive stabilization of the immunoglobulin molecule.
Erntell
M
M
Myhre
E B
EB
Kronvall
G
G
D000907:Antibodies, Bacterial / Q000276:immunology; D000918:Antibody Specificity; D001666:Binding Sites, Antibody; D001667:Binding, Competitive; D004731:Endotoxins / Q000276:immunology; D006801:Humans; D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G / Q000378:metabolism*; D007143:Immunoglobulin Heavy Chains / Q000502:physiology*; D007142:Immunoglobulin gamma-Chains / Q000502:physiology*; D007700:Kinetics; D011961:Receptors, Fc / Q000032:analysis; D017452:Receptors, IgG; D013210:Staphylococcus / Q000276:immunology; D013291:Streptococcus / Q000276:immunology / Q000378:metabolism*
D000907:Antibodies, Bacterial; D004731:Endotoxins; D007140:Immunoglobulin Fab Fragments; D007074:Immunoglobulin G; D007143:Immunoglobulin Heavy Chains; D007142:Immunoglobulin gamma-Chains; D011961:Receptors, Fc; D017452:Receptors, IgG; C016110:staphylolysin