Cross-Species Reactivity and Differential Anti-PRRSV Activities of CD163 SRCR4/SRCR5 Monoclonal Antibodies

CD163 not only acts as an essential receptor for porcine reproductive and respiratory syndrome virus (PRRSV) infection but also serves as a barrier to cross-species cellular infection by arteriviruses. Among its domains, the scavenger receptor cysteine-rich 5 (SRCR5) domain of CD163 is functionally indispensable. In this study, two monoclonal antibodies (mAbs), designated 5A and 11D, were developed against the SRCR4-6 region of porcine CD163. The linear epitopes recognized by mAbs 5A and 11D were identified as 546CEGHESHLSLCPVAP560 in SRCR5 and 449WDCKNW454 in SRCR4, respectively. Crystal structural analysis and sequence alignment showed that the 546CEGHESHLSLCPVAP560 epitope resides in the long loop 5-6 of SRCR5, which is a key structural region responsible for ligand binding. Meanwhile, the 449WDCKNW454 epitope is located within a highly conserved region of SRCR4, which confers broad cross-species reactivity. Notably, mAb 5A reduced PRRSV infection, while mAb 11D exhibited no anti-PRRSV activity in target cells. Collectively, this study provides essential molecular tools for exploring CD163-domain-dependent cross-species reactivity and developing anti-PRRSV strategies.