Assessment of the Macrophage Scavenger Receptor CD163 in Mediating Glaesserella parasuis Infection of Host Cells

SIMPLE SUMMARY: The macrophage CD163 surface glycoprotein is a member of the scavenger receptor cysteine-rich (SRCR) family class B. It has been identified as the receptor for hemoglobin–haptoglobin (Hb-Hp) complexes and erythroblasts, and it is the key trigger in host–pathogen interactions. Previous studies have implicated porcine CD163 in macrophage activation delay upon infection with virulent G. parasuis strains, while its exact roles in sensing G. parasuis infection have not yet been assessed. Here, we investigated the role of CD163 in mediating the adhesion and immune response of G. parasuis using in vitro host–pathogen interaction models. We provide evidence that CD163 plays a minor role, unlike those seen in infections with other pathogens, in mediating G. parasuis infection. ABSTRACT: The macrophage CD163 surface glycoprotein is a member of the SRCR family class B, which has been identified as the key trigger in host–pathogen interactions, but its specific roles in sensing Glaesserella parasuis (G. parasuis) infection are largely unknown. Here, we investigated porcine CD163 in mediating the adhesion and immune response of G. parasuis using in vitro host–bacteria interaction models. CD163-overexpressing Chinese hamster ovary K1 cells (CHO-K1) showed obvious subcellular localization in the cytoplasm, especially in the cytomembrane. Although detection using scanning electron microscopy (SEM) confirmed the bacterial adhesion, there was no significant difference in the adhesion of G. parasuis to CHO-K1 cells between the presence and absence of CD163. In addition, similar results were observed in 3D4/21 cells. Meanwhile, bindings of G. parasuis to nine synthetic peptides, the bacterial binding motifs within SRCR domains of CD163, were weak based on a solid-phase adhesion assay and agglutination assay. Moreover, CD163 had no effect on the expression of G. parasuis-induced inflammatory cytokines (IL-6, INF-γ, IL-10, IL-4 and TGF-β) in CHO-K1 cells. In conclusion, these findings indicate that porcine CD163 plays a minor role in sensing G. parasuis infection.