Characterisation of a mouse monoclonal anti-idiotype reactive with a V region sequence commonly used by human immunoglobulins

Background-A mouse monoclonal antibody (2C7/IgG2b kappa) has been described recently, which is directed against the major house dust mite allergen Der p 1, and whose epitope specificity is representative of a major component of the human IgE anti-Der p 1 response. Aims-To characterise an anti-idiotypic antibody (2G10/IG1 kappa) raised against monoclonal antibody 2C7 as surrogate human IgE anti-Der p 1. Methods-The specificity of the antiidiotype antibody 2G10 was determined by competitive inhibition experiments using human and mouse immunoglobulins of known V-H gene families. The epitope recognised by monoclonal antibody 2G10 was located on the molecular model of the Fv (fragment variable) region of monoclonal antibody 2C7. Results-The data suggest that monoclonal antibody 2G10 is directed against a crossreactive idiotype on human IgE that is shared by polyclonal IgG. Competitive inhibition studies against human immunoglobulins, of globulins, representative of V(H)2, V(H)3, and V(H)4 gene families, showed that monoclonal antibody 2G10 is mostly likely to be directed against sequences encoded by either V(H)3 or V(H)4 genes. The fact that monoclonal antibody 2G10 binds to the humanised (complementarity determining region (CDR) grafted) CAMPATH-1H antibody, but not to the original rat CAMPATH-1 YTH34.5.6 antibody, indicates that it is directed against a framework region rather than the CDRs. Analysis of amino acids in the V-H region for charge, hydrophobicity, and accessibility suggests that reactivity with monoclonal antibody 2G10 is defined by a hexapeptide spanning residues 74-79 within framework region 3. Conclusion-The anti-idiotype monoclonal antibody 2G10 could potentially be used as a probe for determining the contribution of the V(H)3 and V(H)4 gene segments to antigenic specificity.