RAGE Is a Receptor for SARS-CoV-2 N Protein and Mediates N Protein-induced Acute Lung Injury.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid protein (N-protein) increases early in body fluids during infection and has recently been identified as a direct inducer for lung injury. However, the signal mechanism of N-protein in the lung inflammatory response remains poorly understood. The goal of this study was to determine whether RAGE (receptor for advanced glycation endproducts) participated in N-protein-induced acute lung injury. The binding between N-protein and RAGE was examined via assays for protein-protein interaction. To determine the signaling mechanism in vitro, cells were treated with recombinant N-protein and assayed for the activation of the RAGE/MAPK (mitogen-activated protein kinase)/NF-ĸB pathway. RAGE deficiency mice and antagonist were used to study N-protein-induced acute lung injury in vivo. Binding between N-protein and RAGE was confirmed via flow cytometry-based binding assay, surface plasmon resonance, and ELISA. Pull-down and coimmunoprecipitation assays revealed that N-protein bound RAGE via both N-terminal and C-terminal domains. In vitro, N-protein activated the RAGE-ERK1/2-NF-ĸB signaling pathway and induced a proinflammatory response. RAGE deficiency subdued N-protein-induced proinflammatory signaling and response. In vivo, RAGE was upregulated in the BAL and lung tissue after recombinant N-protein insult. RAGE deficiency and small molecule antagonist partially protected mice from N-protein-induced acute lung injury. Our study demonstrated that RAGE is a receptor for N-protein. RAGE is partially responsible for N-protein-induced acute lung injury and has the potential to become a therapeutic target for treating coronavirus disease.

Non-spike and spike-specific memory T cell responses after the third dose of inactivated COVID-19 vaccine.

Background: During the COVID-19 epidemic, vaccination has become the most safe and effective way to prevent severe illness and death. Inactivated vaccines are the most widely used type of COVID-19 vaccines in the world. In contrast to spike-based mRNA/protein COVID-19 vaccines, inactivated vaccines generate antibodies and T cell responses against both spike and non-spike antigens. However, the knowledge of inactivated vaccines in inducing non-spike-specific T cell response is very limited. Methods: In this study, eighteen healthcare volunteers received a homogenous booster (third) dose of the CoronaVac vaccine at least 6 months after the second dose. CD4+ and CD8+ T cell responses against a peptide pool from wild-type (WT) non-spike proteins and spike peptide pools from WT, Delta, and Omicron SARS-CoV-2 were examined before and 1-2 weeks after the booster dose. Results: The booster dose elevated cytokine response in CD4+ and CD8+ T cells as well as expression of cytotoxic marker CD107a in CD8+ T cells in response to non-spike and spike antigens. The frequencies of cytokine-secreting non-spike-specific CD4+ and CD8+ T cells correlated well with those of spike-specific from WT, Delta, and Omicron. Activation-induced markers (AIM) assay also revealed that booster vaccination elicited non-spike-specific CD4+ and CD8+ T cell responses. In addition, booster vaccination produced similar spike-specific AIM+CD4+ and AIM+CD8+ T cell responses to WT, Delta, and Omicron, indicting strong cross-reactivity of functional cellular response between WT and variants. Furthermore, booster vaccination induced effector memory phenotypes of spike-specific and non-spike-specific CD4+ and CD8+ T cells. Conclusions: These data suggest that the booster dose of inactive vaccines broadens both non-spike-specific and spike-specific T cell responses against SARS-CoV-2.