CD169-mediated restrictive SARS-CoV-2 infection of macrophages induces pro-inflammatory responses

Abstract

Exacerbated and persistent innate immune response marked by pro-inflammatory cytokine expression is thought to be a major driver of chronic COVID-19 pathology. Although macrophages are not the primary target cells of SARS-CoV-2 infection in humans, viral RNA and antigens in activated monocytes and macrophages have been detected in post-mortem samples, and dysfunctional monocytes and macrophages have been hypothesized to contribute to a protracted hyper-inflammatory state in COVID-19 patients. In this study, we demonstrate that CD169, a myeloid cell specific I-type lectin, facilitated ACE2-independent SARS-CoV-2 fusion and entry in macrophages. CD169-mediated SARS-CoV-2 entry in macrophages resulted in expression of viral genomic and subgenomic RNAs with minimal viral protein expression and no infectious viral particle release, suggesting a post-entry restriction of the SARS-CoV-2 replication cycle. Intriguingly this post-entry replication block was alleviated by exogenous ACE2 expression in macrophages. Restricted expression of viral genomic and subgenomic RNA in CD169+ macrophages elicited a pro-inflammatory cytokine expression (TNFα, IL-6 and IL-1β) in a RIG-I, MDA-5 and MAVS-dependent manner, which was suppressed by remdesivir treatment. These findings suggest that de novo expression of SARS-CoV-2 RNA in macrophages contributes to the pro-inflammatory cytokine signature and that blocking CD169-mediated ACE2 independent infection and subsequent activation of macrophages by viral RNA might alleviate COVID-19-associated hyperinflammatory response.

Macrophage ACE2 is necessary for SARS-CoV-2 replication and subsequent cytokine responses that restrict continued virion release

“…In lung tissue or BAL from COVID-19 patients, the proportion of macrophages positive for viral RNA is much higher than that of macrophages positive for ACE2 ( 8 , 20 , 49 ). Our data suggest that this is not because of ACE2-independent SARS-CoV-2 entry into and replication within macrophages, in contrast to a study that reported CD169-dependent, ACE2-independent macrophage infection ( 33 ). Instead, we expect that macrophages positive for viral RNA may be ACE2-negative macrophages with phagocytosed virions (as observed here in culture), extracellular viral RNA, or virus-infected cells ( 50 ).…”

“…SARS-CoV-2 entry receptors other than ACE2 are reported, including the C-type lectin receptors ( 26 ) and CD169 ( 33 ). Because the assays that we used to measure viral protein and RNA could not distinguish whether the virus was intracellular or extracellular (Fig.…”

Comprehensive analysis of SARS‐CoV‐2 receptor proteins in human respiratory tissues identifies alveolar macrophages as potential virus entry site

“…CD169 was shown to be expressed on circulating monocytes 50 and dendritic cells 51 . This further highlights mononuclear phagocytes as important potential viral entry cells 52,53 . In addition, CD169 is a known viral entry receptor with pathogen recognition ability 54 .…”

“…51 This further highlights mononuclear phagocytes as important potential viral entry cells. 52,53 In addition, CD169 is a known viral entry receptor with pathogen recognition ability. 54 Here, we observed consistent expression of CD169 in sinonasal, conjunctival and bronchiolar epithelium, which supports its suggested role as an attachment receptor for SARS-CoV-2.…”

Effects of Different Types of Recombinant SARS-CoV-2 Spike Protein on Circulating Monocytes Structure

“…Resting monocytes harbor an abundant concentration of ACE2 and transmembrane serine protease 2 (TMPRSS2) in their cytoplasm, which upon stimulation, can be rapidly transported to the cell surface, where these two proteins are used by SARS-CoV-2 for binding to and fusing with the cell through its spike protein [15]. Virus-cell interaction may also be mediated by the myeloid cell specific I-type lectin CD169, to which the spike protein can efficiently bind [16].…”