Analysis of cross-species IgG binding to human and mouse Fcgamma receptors (FcγRs) (138.29)

Abstract Monoclonal antibodies from various species are in therapeutic and diagnostic use and are used extensively in cell depletion studies in rodents. Therefore, in the present investigation the cross-species IgG binding to FcγRs were performed using recombinant dimeric soluble form of human and mouse FcγRs. We observed that human CD16A was able to bind to rabbit IgG better than human CD32AH and CD32AR. The binding specificity is hCD16>hCD32AH>>hCD32R. Both hCD32A alleles were able to bind mouse and rat IgG subtypes, whereas hCD16 binds weakly. hCD32AR binds mouse IgG1, IgG2a and IgG2b but not IgG3 (IgG1>>IgG2a≥IgG2b) whereas CD32AH binds IgG2a and IgG2b (IgG2a≥IgG2b) only not IgG1 and IgG3. With rat IgG subtypes, hCD32AR binds IgG1>IgG2a>>IgG2b and hCD32AH binds IgG1>IgG2b>IgG2a whereas neither hCD32A alleles bound to IgG2c. We observed that hCD32AR allele binds stronger than hCD32AH to rat IgG. With human IgG subtypes, both hCD16A and hCD32AR binds IgG3>IgG1>>>IgG2≥IgG4, whereas hCD32AH binds IgG3>IgG1>IgG2>>>IgG4. We have also characterized binding specificity of mouse FcγRs (mCD16A, mCD32B and mFcRIV) to rabbit and mouse IgGs. All three mFcγRs binds to rabbit IgG. For mouse IgG subtypes, mCD16A binds IgG2b>IgG2a≥IgG1, mCD32B binds IgG1≥IgG2b>IgG2a, whereas FcRIV binds IgG2a≥IgG2b only, none of the mFcγR bound to mIgG3. In conclusion, cross-species FcγR binding to different IgGs must be taken into consideration when IgG based therapeutics and diagnostics are evaluated in rodents.