Human Cytomegalovirus Envelope Glycoproteins B and H Are Necessary for TLR2 Activation in Permissive Cells

Abstract

Human CMV (HCMV) is a ubiquitous member of the Herpesviridae family and an opportunistic pathogen that poses significant health risks for immunocompromised patients. HCMV pathogenesis is intimately tied to the immune status of the host, thus characterization of the innate immune response to HCMV infection is critical for understanding disease progression. Previously, we identified TLR2 as a host factor that detects and initiates inflammatory cytokine secretion in response to HCMV independent of viral replication. In this study, we show that two entry-mediating envelope gp, gp B (gB) and gp H (gH), display determinants recognized by TLR2. Neutralizing Abs against TLR2, gB and gH inhibit inflammatory cytokine responses to HCMV infection, suggesting that inflammatory cytokine stimulation by HCMV is mediated by interactions between these envelope gp and TLR2. Furthermore, both gB and gH coimmunoprecipitate with TLR2 and TLR1, indicating that these envelope gp directly interact with TLR2 and that a TLR2/TLR1 heterodimer is a functional sensor for HCMV. Because our previous studies were conducted in model cell lines, we also show that TLR2 is expressed by HCMV permissive human fibroblast cell strains, and that TLR2 is a functional sensor in these cells. This study further elucidates the importance and potency of envelope gp as a class of molecules displaying pathogen-associated molecular patterns that are recognized with immediate kinetics by TLRs in permissive cells.

Herpesviral infection and Toll-like receptor 2

“…This strategy may be beneficial to the virus in order to induce upregulation of viral entry receptors but may also serve the host in favoring a rapid respond to viral invaders (Bieback et al, 2002;Zhu et al, 2007). Thus far, a large body of works demonstrate that TLR2 has been implicated in the recognition of structural components of several viruses (Bieback et al, 2002;Duesberg et al, 2002;Dolganiuc et al, 2004;Cooper et al, 2005), as well as members of the herpesvirus family, including HSV, VZV, murine gammaherpesvirus-68 (MHV-68), CMV, and EBV (Compton et al, 2003;Kurt-Jones et al, 2004;Wang et al, 2005a;Boehme et al, 2006;Sato et al, 2006;Szomolanyi-Tsuda et al, 2006;Gaudreault et al, 2007;Ariza et al, 2009;Michaud et al, 2010).…”

“…Like HSV, using HEK293 cells stably transfected with TLR2 expression vector, TLR2 in patients has been demonstrated to play a role in the early stage of CMV infection. And, HCMV virions are capable of stimulating an inflammatory cytokine secretion from human and mouse macrophages through TLR2-dependent activation of NF-κB (Compton et al, 2003;Boehme et al, 2006). Furthermore, similar to most TLR2-mediated responses, signaling of TLR2 in response to CMV is strongly enhanced by the presence of CD14.…”

“…Therefore, the defect in early antiviral control was associated with reduction of NK cell population in the spleen and liver 4 days post-infection and may be related to NK cell recruitment, proliferation, or sensitivity to apoptosis (Szomolanyi-Tsuda et al, 2006). Although the structural component(s) important for the recognition of HSV, VZV, and MHV-68 have not been identified, interaction with TLR2 for NF-κB activation and inflammatory cytokine secretion, likely in heterodimeric form with TLR1, involves two CMV entry-mediating envelope glycoproteins gB and gH in permissive cells (Boehme et al, 2006), suggesting that multiple glycoproteins from a single virus can display recognition motifs.…”

“…Clinically, a R753Q SNP in TLR2 in liver transplant patients is associated with a significantly higher degree of CMV replication, and homozygosity for this polymorphism confers increased risk of CMV disease (Kijpittayarit et al, 2007), whereas Boehme et al provides the biologic explanation for this clinical observation by demonstrating that variant cells with TLR2 R753Q SNP failed to recognize CMV gB (Boehme et al, 2006). This immunologic impairment could serve as a biologic mechanism underlying the association between TLR2 R753Q polymorphism and CMV disease in humans.…”

Interplay between human cytomegalovirus and dendritic cells in T cell activation

“…Interactions between the envelope glycoprotein gB of HCMV and TLR2 have been described [11]. Binding to the receptor, induced secretion of proinXammatory cytokines but did not take part in the activation of IFN-/ secretion by infected cells [12], suggesting that TLR2 activation by HCMV could not beneWt the host.…”