title: A non-immune interaction between the light chain of human immunoglobulin and a surface component of a Peptococcus magnus strain.
abstract: The immunoglobulin-binding capacity of a Peptococcus magnus strain was studied in a sensitive binding assay using purified human immunoglobulin preparations. The P. magnus strain 312 was capable of binding 48% of polyclonal IgG. Twenty-four of 40 purified myeloma proteins (60%) representing immunoglobulin classes A, G and M showed definite reactivity with an uptake level ranging from 45 to 90%. The remaining 16 monoclonal proteins were non-reactive, binding less than 15%. One myeloma protein with antistaphylolysin and two with antistreptolysin O specificity, i.e. monoclonal proteins with defined antigen specificity, were highly reactive. Binding capacity was observed in all four IgG subclasses and in Ig classes A and M. Twenty-three of 27 myeloma proteins of kappa type were reactive but only one of 13 myeloma proteins of lambda type interacted with the P. magnus strain. Isotope-labelled Fab gamma, F(ab')2 gamma and F(ab')2 alpha fragments were effectively bound by the strain. IgG Fc fragments were completely non-reactive. Isolated light immunoglobulin chains inhibited in a dose-dependent way the uptake of intact IgG to bacteria. Purified heavy chains were non-inhibitory. Isotope-labelled antistaphylolysin IgG F(ab')2 fragments preincubated with staphylolysin were as reactive as free antibody fragments, suggesting that the bacterial binding structure is located outside the antibody-combining site. The immunoglobulin reactivity of P. magnus was not affected by heating the bacteria to 80 degrees C for 5 min nor by treatment with trypsin or sodium metaperiodate. Digestion of 2 X 10(9) organisms with 100 micrograms of pepsin and papain reduced the binding by 58 and 90%, respectively. These data indicate that the binding of immunoglobulin to P. magnus is a non-immune reactivity mediated by a heat-stable surface protein interacting with specific sites on the light chain of the immunoglobulin molecule.
mesh_terms: D000911:Antibodies, Monoclonal / Q000502:physiology; D001665:Binding Sites / Q000187:drug effects; D001667:Binding, Competitive; D004306:Dose-Response Relationship, Immunologic; D006801:Humans; D007128:Immunoglobulin Fragments; D007074:Immunoglobulin G / Q000378:metabolism; D007143:Immunoglobulin Heavy Chains / Q000502:physiology; D007147:Immunoglobulin Light Chains / Q000502:physiology*; D009194:Myeloma Proteins / Q000378:metabolism; D010460:Peptococcus / Q000378:metabolism*; D011485:Protein Binding
chemical_list: D000911:Antibodies, Monoclonal; D007128:Immunoglobulin Fragments; D007074:Immunoglobulin G; D007143:Immunoglobulin Heavy Chains; D007147:Immunoglobulin Light Chains; D009194:Myeloma Proteins