Sialoadhesin and CD163 join forces during entry of the porcine reproductive and respiratory syndrome virus

Abstract

The porcine reproductive and respiratory syndrome virus (PRRSV) shows a restricted tropism for subsets of porcine macrophages in vivo. To date, two PRRSV receptors have been identified on primary macrophages, heparan sulphate for binding and sialoadhesin for binding and internalization. However, additional factors are needed because the expression of both receptors in non-permissive cells results in virus internalization but not in virus uncoating and productive infection. Recently, CD163 was described as a PRRSV receptor on Marc-145 cells that renders non-permissive cells susceptible to PRRSV. Therefore, the potential role of CD163 in PRRSV entry in macrophages and its potential interplay with sialoadhesin were studied. Incubation of macrophages at 37 6C with either sialoadhesin-or CD163-specific antibodies reduced PRRSV infection by up to 75 %, while infection was completely blocked by a combination of both antibodies. When incubated at 4 6C, only sialoadhesin-and not CD163-specific antibodies reduced PRRSV infection. In addition, confocal analysis of PRRSV entry in non-permissive cells expressing only sialoadhesin showed PRRSV internalization but no uncoating. In contrast, when both sialoadhesin and CD163 were expressed, PRRSV was uncoated upon internalization, resulting in productive infection. Virus internalization was not observed when only CD163 was expressed; although, cells became productively infected. Thus, sialoadhesin is confirmed as a PRRSV internalization receptor and CD163 is shown to be involved in PRRSV entry, probably during uncoating. Co-expression of recombinant sialoadhesin and CD163 in non-permissive cells increased virus production 10-100 times compared with cells expressing only CD163, sustaining the requirement of both for efficient PRRSV infection. INTRODUCTIONA 'mystery swine disease' appeared in the 1980s and has been present ever since in the pig industry, causing important economical losses worldwide (Neumann et al., 2005). The causative agent, designated porcine reproductive and respiratory syndrome virus (PRRSV), was isolated in the Netherlands in 1991 and shortly after in the USA (Collins et al., 1992;Neumann et al., 2005;Wensvoort et al., 1991). PRRSV, a small enveloped positive-stranded RNA virus, is classified in the order Nidovirales, family Arteriviridae, genus Arterivirus together with equine arteritis virus, lactate dehydrogenase-elavating virus and simian hemorrhagic fever virus based on similar morphology, genomic organization, replication strategy and protein composition (Cavanagh, 1997). In addition, they share a very narrow host tropism and a marked preference for cells of the monocyte-macrophage lineage. More specifically, in vivo, PRRSV infects subpopulations of differentiated macrophages, with alveolar macrophages being the major target cells during acute infection (Duan et al., 1997b; Teifke et al., 2001). In vitro, PRRSV replicates in primary cultures of alveolar macrophages and to some extent in peripheral blood monocytes, with pre-treatment of alpha interfero...

Assessing the functionality of viral entry-associated domains of porcine reproductive and respiratory syndrome virus during inactivation procedures, a potential tool to optimize inactivated vaccines

“…There are some neutralizing epitopes known on GP5 and GP4 [39,48,66] and there are possibly also neutralizing epitopes on GP3 [5], but it is not known if other important epitopes exist and which neutralizing epitopes are most important. Previous results from our lab showed that PRRSV neutralizing antibodies block infection by preventing the interaction of PRRSV with the internalization receptor sialoadhesin (Sn) on the target cells, macrophages [15,16,60,61]. This indicates that neutralizing antibodies are directed to the viral epitopes that are involved in the attachment to the PRRSV receptors and internalization into the macrophage [15].…”

“…To investigate if entry of the inactivated PRRSV in macrophages occurred via Sn and CD163 as described for infectious PRRSV [60,61], and not simply taken up by phagocytosis, entry was also determined using a phagocytosis inhibitor wortmannin. After treatment of the macrophages with the phagocytosis inhibitor wortmannin, untreated PRRSV still attached to and internalized into macrophages.…”

Comparative Analysis of Monocyte Subsets in the Pig

“…A major imperative for the study of the CD163 + monocyte subset in pigs has been the putative function of CD163 as a receptor for the important pathogen PRRSV (19,20,46,47). Monocytes purified based on CD14 expression, or adhesion, were found to lack CD163 and to be nonpermissive for the virus (46,47).…”

“…The main focus in the pig has been on a distinct marker, CD163 (18), because of the role of CD163 in cellular entry into macrophages of the important porcine pathogen porcine reproductive and respiratory syndrome virus (19). The expression of this marker correlated with differential expression of the mouse/human markers CCR2 and CX3CR1 at the mRNA level (20).…”

CD163, a Hemoglobin/Haptoglobin Scavenger Receptor, After Intracerebral Hemorrhage: Functions in Microglia/Macrophages Versus Neurons

“…For instance, Fabriek et al found a role of macrophage CD163 in binding of Gram-positive and Gram-negative bacteria [12]. Van Gorp et al found that macrophage CD163 also bound porcine reproductive and respiratory syndrome virus [13].…”