The Neutralization of Type I IFN Biologic Actions by Anti-IFNAR-2 Monoclonal Antibodies Is Not Entirely

A panel of monoclonal antibodies (mAb) derived against human interferon-a/b receptor-2 (IFNAR-2) was evaluated for their ability to antagonize the biologic effects of type 1 interferons (IFN-a1, IFN-a2a, and IFN-b). Anti-IFNAR-2 mAb 117.7, 35.9, 53.2, and 51.44 neutralized type I IFN-mediated antiviral, antiprolifera-tive, and major histocompatibility complex (MHC) class I upregulation functions. However, only mAb 51.44 neutralized IFN-a2a and IFN-b-mediated natural killer (NK) cell cytotoxicity. In BIAcore and cell binding studies, only mAb 51.44 and 234.28 inhibited IFN-a2a and IFN-b binding to its receptor. The receptor block-ade by mAb 51.44 and 234.28 resulted in the inhibition of IFN-a2a and IFN-b-induced tyrosine phosphory-lation of Jak1, Tyk2, Stat1/2/3, and IFNAR-1/2 and inhibition of IFN-stimulated gene factor 3 (ISGF3) for-mation. mAb 117.7, 35.9, and 53.2, although antagonists of IFN’s biologic activities, did not block the binding of IFN-a/b to its receptor. The 117.7 mAb, representative of this class of receptor nonblocking mAb, induced hyper-tyrosine phosphorylation of IFNAR-2 in the presence of IFN-a/b but did not inhibit IFN-a/b-induced Jak-Stat tyrosine phosphorylation and ISGF3 complex formation. These results show that the neutralization of type I IFN biologic actions by anti-IFNAR-2 mAb cannot be entirely explained by inhibition of Jak-Stat tyrosine phosphorylation. 97