Poxvirus Infection-Associated Downregulation of C-Type Lectin-Related-b Prevents NK Cell Inhibition by NK Receptor Protein-1B

Abstract

Innate immune recognition of virus-infected cells includes NK cell detection of changes to endogenous cell-surface proteins through inhibitory receptors. One such receptor system is the NK cell receptor protein-1B (NKR-P1B) and its ligand C-type lectin-related-b (Clr-b). NKR-P1B and Clr-b are encoded within the NK cell gene complex, a locus that has been linked to strain-dependent differences in susceptibility to infection by poxviruses. In this study, we report the impact of vaccinia virus (VV) and ectromelia virus infection on expression of Clr-b and Clr-b–mediated protection from NK cells. We observed a loss of Clr-b cell-surface protein upon VV and ectromelia virus infection of murine cell lines and bone marrow-derived macrophages. The reduction of Clr-b is more rapid than MHC class I, the prototypic ligand of NK cell inhibitory receptors. Reduction of Clr-b requires active viral infection but not expression of late viral genes, and loss of mRNA appears to lag behind loss of Clr-b surface protein. Clr-b–mediated protection from NK cells is lost following VV infection. Together, these results provide the second example of Clr-b modulation during viral infection and suggest reductions of Clr-b may be involved in sensitizing poxvirus-infected cells to NK cells.

Modulation of Clr Ligand Expression and NKR-P1 Receptor Function during Murine Cytomegalovirus Infection

“…In agreement with this, similar findings were reported for mClr-b in a mouse model of orthopoxvirus (VV, ECTV) infection [15] . Here, we provide evidence for a conserved mechanistic response for both mClr-b and rClr-11 in response to cross-species CMV infection.…”

“…We next tested the effects of the proteasomal inhibitor, MG132, on MCMV infection-mediated Clr-b loss, as we previously showed that inhibition of the Ub-proteasome degradation pathway could prevent genotoxic stressmediated Clr-b downregulation [14,15] . MG132 was effective at blocking MCMV-mediated Clr-b loss, albeit incompletely even at high doses (online suppl.…”

“…fig. 2) or that ActD may also promote stress-mediated mClr-b downregulation [14,15] . Thus, we attempted to titrate ActD levels to achieve only partial Clr-b loss, while maintaining partial inhibition of IE genes; however, such an optimal dose was not possible, making inferences on IE gene blockade inconclusive (online suppl.…”

A Viral Immunoevasin Controls Innate Immunity by Targeting the Prototypical Natural Killer Cell Receptor Family

“…The murine NKR-P1B ligand, , is rapidly lost in response to cellular infection by diverse viruses Voigt et al, 2007;Williams et al, 2012). However, MCMV-infected fibroblasts also induce a Clr-b-independent NKR-P1B ligand .…”

“…Yet to date, NKR-P1C, the prototypical NK1.1 antigen in B6 mice (Glimcher et al, 1977;Koo and Peppard, 1984;Ryan et al, 1992), and NKR-P1A remain orphan-activating receptors with unknown physiological ligands. On the other hand, the paired NKR-P1F and NKR-P1G receptors recognize overlapping ''self'' Clr (Clec2) ligands to balance signals during NK cell education and effector responses, while the inhibitory NKR-P1B receptor recognizes the broadly expressed self Clr-b (Clec2d) ligand (Carlyle et al, 2004;Chen et al, 2011;Iizuka et al, 2003;Kveberg et al, 2009 been shown to be involved in ''missing-self'' recognition under diverse pathological states (Kirkham and Carlyle, 2014), including cancer (Carlyle et al, 2004), genotoxic and cellular stress (Fine et al, 2010), hematopoietic transplantation , immune escape of primary lymphoma cells , and cytomegalovirus and poxvirus infection Voigt et al, 2007;Williams et al, 2012), while the remainder of the self Clr ligands remain less well characterized. Among pathogens recognized by NK cells, cytomegaloviruses (CMV) demonstrate co-evolution with their natural hosts, likely due to cycles of natural selection for viral versus host fitness.…”