Cross-Species Reactivity and Differential Anti-PRRSV Activities of CD163 SRCR4/SRCR5 Monoclonal Antibodies
Simple Summary Porcine reproductive and respiratory syndrome virus (PRRSV) infection causes substantial economic losses to the global swine industry. PRRSV invades host target cells via receptor-mediated endocytosis, and CD163 is the most important receptor for PRRSV entry. Among the CD163 domains, the scavenger receptor cysteine-rich 5 (SRCR5) domain is essential for PRRSV infection. Therefore, CD163 and its SRCR5 are commonly selected as targets for developing anti-PRRSV strategies, including for the generation of CD163-SRCR5 knockout pigs. In addition, CD163 divergence also serves as a barrier to cross-species cellular infection by arteriviruses. Nevertheless, CD163 monoclonal antibodies (mAbs) with defined cross-species reactivity and anti-PRRSV activities have rarely been characterized. Here, we developed two mAbs against porcine CD163. Epitope mapping demonstrated that mAb 5A recognizes a novel epitope within the long loop 5-6 of the SRCR5 domain, while mAb 11D targets a conserved epitope within the SRCR4 domain. Functional validation revealed that mAb 5A can inhibit PRRSV infection, while mAb 11D cannot. Remarkably, mAb 11D exhibits broader cross-species reactivity than mAb 5A. Overall, this study provides a solid foundation for elucidating CD163-domain-dependent biological functions.