Elucidating the Role of the Complement Control Protein in Monkeypox Pathogenicity

Abstract

Monkeypox virus (MPXV) causes a smallpox-like disease in humans. Clinical and epidemiological studies provide evidence of pathogenicity differences between two geographically distinct monkeypox virus clades: the West African and Congo Basin. Genomic analysis of strains from both clades identified a ∼10 kbp deletion in the less virulent West African isolates sequenced to date. One absent open reading frame encodes the monkeypox virus homologue of the complement control protein (CCP). This modulatory protein prevents the initiation of both the classical and alternative pathways of complement activation. In monkeypox virus, CCP, also known as MOPICE, is a ∼24 kDa secretory protein with sequence homology to this superfamily of proteins. Here we investigate CCP expression and its role in monkeypox virulence and pathogenesis. CCP was incorporated into the West African strain and removed from the Congo Basin strain by homologous recombination. CCP expression phenotypes were confirmed for both wild type and recombinant monkeypox viruses and CCP activity was confirmed using a C4b binding assay. To characterize the disease, prairie dogs were intranasally infected and disease progression was monitored for 30 days. Removal of CCP from the Congo Basin strain reduced monkeypox disease morbidity and mortality, but did not significantly decrease viral load. The inclusion of CCP in the West African strain produced changes in disease manifestation, but had no apparent effect on disease-associated mortality. This study identifies CCP as an important immuno-modulatory protein in monkeypox pathogenesis but not solely responsible for the increased virulence seen within the Congo Basin clade of monkeypox virus.

Attenuation of monkeypox virus by deletion of genomic regions

“…These studies have shown that deletion of individual genes can either reduce (Johnston and McFadden, 2004; Senkevich et al, 1994) or enhance (Estep et al, 2011; Ng et al., 2001) replication and virulence. Previous studies that investigated differences in virulence of MPXV strains have predominantly focused on the function and characterization of individual genes, for example, the inhibitor of complement-binding protein (MOPICE), an important anti-inflammatory factor of OPXV (Estep et al, 2011; Hudson et al, 2012). The gene that codes for these enzymes (D14R) is absent in the less virulent west African MPXV strains and has been considered a major virulence factor in Central African MPXV clade infection (Chen et al, 2005).…”

“…Results showed that deletion of D14R in Central African MPXV clade enhanced viral replication in rhesus macaques (Estep et al, 2011). Another report showed that deletion of D14R in Central African MPXV clade subtly reduced morbidity and mortality in prairie dogs, and D14R insertion in West African MPXV clade only affected minor disease manifestations (Hudson et al., 2012). Similar to these previous reports, we have observed that the single deletion of MOPICE gene and B14R gene, an inhibitor of IL-1β-binding protein, in MPXV/Congo increased viral replication and spread after intranasal inoculation of CAST/EiJ and severe combined immunodeficiency (SCID) mice, respectively (Lopera et al, unpublished data).…”

“…Similar to these previous reports, we have observed that the single deletion of MOPICE gene and B14R gene, an inhibitor of IL-1β-binding protein, in MPXV/Congo increased viral replication and spread after intranasal inoculation of CAST/EiJ and severe combined immunodeficiency (SCID) mice, respectively (Lopera et al, unpublished data). These studies suggested that D14R or B14R are not the sole virulence factors responsible for major differences in MPX pathogenesis (Estep et al, 2011; Hudson et al, 2012). …”

“…These genes have evolved specifically to simultaneously inhibit diverse processes such as pattern-recognition receptor signaling, apoptosis, chemokine and cytokine function, and lymphocyte and antibody activity (Fernandez de Marco Mdel et al, 2010; Hammarlund et al., 2008; Kindrachuk et al, 2012; Weaver and Isaacs, 2008). Whereas previous evaluations of MPXV virulence factors have predominantly focused on the function and characterization of individual viral genes, these studies demonstrated that individual genes were not solely responsible for the observed differences in pathogenicity between MPXV clades (Estep et al, 2011; Hudson et al, 2012). In contrast, we evaluated the effect of deletions of large genomic regions in MPXV that contain several host range and IMM genes to facilitate selection of candidate virulence factors involved in pathogenesis.…”

Human Antibody Responses to the Polyclonal Dryvax Vaccine for Smallpox Prevention Can Be Distinguished from Responses to the Monoclonal Replacement Vaccine ACAM2000

“…In contrast to IMV and EEV surface proteins, secreted and intracellular VACV proteins can have an indirect role in protective immunity. For the case of C3L, this secreted VACV protein was shown to enhance pathogenesis of VACV and monkeypoxvirus infections by affecting complement activation (46)(47)(48). As an example of an intracellular antigen recognized by vaccine antibody responses observed in our study, the poxvirus protein O1L enhances virulence by continuous activation of the extracellular signal-regulated kinase (ERK) pathway, which may promote viral replication and dissemination (49).…”