Binding of bovine IgG2(a) and IgG2(b) allotypes to protein A, protein G, and Haemophilus somnus IgBPs

Immunoglobulin binding proteins (IgBPs) are thought to be virulence factors which enable pathogens to evade the host's immune response. Since bovine I gG2 is important in protection against pyogenic infections, the binding cha racteristics of Staphylococcus aureus protein A (PrA), streptococcal protei n G (PrG), or Haemophilus somnus high molecular weight IgBPs to the two bov ine IgG2 allotypes were examined. For PrA or PrG binding of IgG2, guinea pi g red blood cells coated with specific IgG2(a) or IgG2(b) antibodies were u sed in a competitive binding inhibition assay with unlabeled and horseradis h peroxidase-labeled PrA or PrG. To determine which sizes of H. somnus IgBP s bind to the two IgG2 allotypes, im somnus with PI. somnus culture superna tant were probed with anti-DNP IgG2(a) and IgG2(b). This detects only Fc bi nding because anti-DNP does not cross-react with H. somnus antigens. Both I gG2 allotypes bound equally well to PrA and PrG. However, IgG2(b) but not I gG2(a) bound to H. somnus high molecular weight IgBPs. The lack of differen tial binding of bovine IgG2 allotypes to PrA and PrG means that these IgBPs can be considered to be unbiased reagents in assays for detection of bovin e IgG2 or for immunoaffinity purification. The differential binding of H. s omnus IgBPs to the IgG2 allotypes indicates that animals having one allotyp e may be more resistant to H. somnus infection than animals having the othe r allotype. (C) 1999 Elsevier Science B.V. All rights reserved.