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 sub-genomic (sg) 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 gRNA and sgRNA 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 pre- 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.Author SummaryOver-exuberant production of pro-inflammatory cytokine expression by macrophages has been hypothesized to contribute to severity of COVID-19 disease. Molecular mechanisms that contribute to macrophage-intrinsic immune activation during SARS- CoV-2 infection are not fully understood. Here we show that CD169, a macrophage- specific sialic-acid binding lectin, facilitates abortive SARS-CoV-2 infection of macrophages that results in innate immune sensing of viral replication intermediates and production of proinflammatory responses. We identify an ACE2-independent, CD169- mediated endosomal viral entry mechanism that results in cytoplasmic delivery of viral capsids and initiation of virus replication, but absence of infectious viral production. Restricted viral replication in CD169+ macrophages and detection of viral genomic and sub-genomic RNAs by cytoplasmic RIG-I-like receptor family members, RIG-I and MDA5, and initiation of downstream signaling via the adaptor protein MAVS, was required for innate immune activation. These studies uncover mechanisms important for initiation of innate immune sensing of SARS-CoV-2 infection in macrophages, persistent activation of which might contribute to severe COVID-19 pathophysiology.

SARS-CoV-2 infection drives an inflammatory response in human adipose tissue through infection of adipocytes and macrophages

“…It is also important to consider that there is heterogeneity among macrophage populations. Transcriptional profiling enabled us to identify two unique subsets of adipose tissue-resident macrophages, neither of which fell into a classical M1 versus M2 classification, consistent with reports that macrophages in adipose tissue exhibit unique phenotypes ( 39 ). One of these subsets, an inflammatory cluster characterized by high expression IL1B and CCL3 , was preferentially infected.…”

“…As even abortive infection can drive inflammatory responses ( 38 , 39 ), we assessed the production of inflammatory mediators in infected SVC and in differentiated adipocytes. First we assessed IL6 in SVC because of the association between interleukin (IL)-6 and low-grade inflammation in obese individuals ( 40 ), and the critical role of IL-6 in COVID-19 immunopathogenesis ( 41 , 42 ).…”

“…Two studies show productive infection of human alveolar macrophages and MDMs ( 103 , 104 ). However, numerous other studies report abortive infection of monocytes, macrophages, and MDM, hypothesizing that low ACE2 expression or pyroptosis prior to virus production and release lead to abortive infection ( 38 , 39 , 105 – 107 ). Interestingly, the entry into the productively infected alveolar macrophages was ACE2-dependent, whereas in our study and another recent report ( 39 ), entry into macrophages is ACE2-independent and leads to abortive infection.…”

“…Because even abortive infection can drive inflammatory responses (35,36), we assessed the production of inflammatory mediators in infected SVC and in differentiated adipocytes. First, we assessed IL6 Table 1.…”

Exacerbation of Darier’s disease with COVID-19

“…2,3 COVID-19 infection produces a cytokine storm characterized by elevated levels of tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, and IL-1b. 9 TNF-alpha and IL-6 act to downregulate ATP2A2 mRNA levels, which would decrease the capacity of an already dysfunctional SERCA2b calcium pump in DD patients. 10 Furthermore, an abundance of TNF-alpha enhances necroptosis of epithelial cells of the epidermis, potentially compounding acantholysis and apoptosis in the epidermis.…”