van der Donk, L. E. H. | Search bioRxiv

bioRxiv2023

Antibodies against SARS-CoV-2 control complement-induced inflammatory responses to SARS-CoV-2

Dysregulated immune responses contribute to pathogenesis of COVID-19 leading to uncontrolled and exaggerated inflammation observed during severe COVID-19. However, it remains unclear how immunity to SARS-CoV-2 is induced and subsequently controlled. Notably, here we have uncovered an important role for complement in the induction of innate and adaptive immunity to SARS-CoV-2. Complement rapidly opsonized SARS-CoV-2 via the lectin pathway. Complement-opsonized SARS-CoV-2 efficiently interacted with dendritic cells (DCs), inducing type I IFN and pro-inflammatory cytokine responses, which were inhibited by antibodies against the complement receptors (CR)3 and CR4. These data suggest that complement is important in inducing immunity via DCs in the acute phase against SARS-CoV-2. Strikingly, serum from COVID-19 patients as well as monoclonal antibodies against SARS-CoV-2 attenuated innate and adaptive immunity induced by complement-opsonized SARS-CoV-2. Blocking the FcyRII, CD32, restored complement-induced immunity. These data strongly suggest that complement opsonization of SARS-CoV-2 is important for inducing innate and adaptive immunity to SARS-CoV-2. Subsequent induction of antibody responses is important to limit the immune responses and restore immune homeostasis. These data suggest that dysregulation in complement and FcyRII signalling might underlie mechanisms causing severe COVID-19.

immunology↗

bioRxiv2021

SARS-CoV-2 infection activates dendritic cells via cytosolic receptors rather than extracellular TLRs

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes coronavirus disease 2019 (COVID-19), an infectious disease characterized by strong induction of inflammatory cytokines, progressive lung inflammation and potentially multi-organ dysfunction. It remains unclear whether SARS-CoV-2 is sensed by pattern recognition receptors (PRRs) leading to immune activation. Several studies suggest that the Spike (S) protein of SARS-CoV-2 might interact with Toll-like receptor 4 (TLR4) and thereby activate immunity. Here we have investigated the role of TLR4 in SARS-CoV-2 infection and immunity. Neither exposure of isolated S protein, SARS-CoV-2 pseudovirus nor a primary SARS-CoV-2 isolate induced TLR4 activation in a TLR4-expressing cell line. Human monocyte-derived dendritic cells (DCs) express TLR4 but not ACE2, and DCs were not infected by a primary SARS-CoV-2 isolate. Notably, neither S protein nor the primary SARS-CoV-2 isolate induced DC maturation or cytokines, indicating that both S protein and SARS-CoV-2 virus particles do not trigger extracellular TLRs, including TLR4. Ectopic expression of ACE2 in DCs led to efficient infection by SARS-CoV-2. Strikingly, infection of ACE2-positive DCs induced type I IFN and cytokine responses, which was inhibited by antibodies against ACE2. These data strongly suggest that not extracellular TLRs but intracellular viral sensors are key players in sensing SARS-CoV-2. These data imply that SARS-CoV-2 escapes direct sensing by TLRs, which might underlie the lack of efficient immunity to SARS-CoV-2 early during infection. Author summaryThe immune system needs to recognize pathogens such as SARS-CoV-2 to initiate antiviral immunity. Dendritic cells (DCs) are crucial for inducing antiviral immunity and are therefore equipped with both extracellular and intracellular pattern recognition receptors to sense pathogens. However, it is unknown if and how SARS-CoV-2 activates DCs. Recent research suggests that SARS-CoV-2 is sensed by extracellular Toll-like receptor 4 (TLR4). We have previously shown that DCs do not express ACE2, and are therefore not infected by SARS-CoV-2. Here we show that DCs do not become activated by exposure to viral Spike proteins or SARS-CoV-2 virus particles. These findings suggest that TLR4 and other extracellular TLRs do not sense SARS-CoV-2. Next, we expressed ACE2 in DCs and SARS-CoV-2 efficiently infected these ACE2-positive DCs. Notably, infection of ACE2-positive DCs induced an antiviral immune response. Thus, our study suggests that infection of DCs is required for induction of immunity, and thus that intracellular viral sensors rather than extracellular TLRs are important in sensing SARS-CoV-2. Lack of sensing by extracellular TLRs might be an escape mechanism of SARS-CoV-2 and could contribute to the aberrant immune responses observed during COVID-19.

immunology↗