Cui, Weiguo

Abstract Thromboembolic complication is common in severe coronavirus disease 2019 (COVID-19), leading to an investigation into the presence of prothrombotic antibodies akin to those found in heparin-induced thrombocytopenia (HIT). In a study of samples from 130 hospitalized patients, collected 3.6 days after COVID-19 diagnosis, 80% had immunoglobulin G (IgG) antibodies recognizing complexes of heparin and platelet factor 4 (PF4; PF4/H), and 41% had antibodies inducing PF4-dependent P-selectin expression in CpG oligodeoxynucleotide–treated normal platelets. Unlike HIT, both PF4/H-reactive and platelet-activating antibodies were found in patients with COVID-19 regardless of recent heparin exposure. Notably, PF4/H-reactive IgG antibodies correlated with those targeting the receptor-binding domain (RBD) of the severe acute respiratory syndrome coronavirus 2 spike protein. Moreover, introducing exogenous RBD to or removing RBD-reactive IgG from COVID-19 plasma or IgG purified from COVID-19 plasma significantly reduced their ability to activate platelets. RBD-specific antibodies capable of platelet activation were cloned from peripheral blood B cells of patients with COVID-19. These antibodies possessed sequence motifs in the heavy-chain complementarity-determining region 3 (HCDR3), resembling those identified in pathogenic HIT antibodies. Furthermore, IgG+ B cells having these HCDR3 signatures were markedly expanded in patients with severe COVID-19. Importantly, platelet-activating antibodies present in patients with COVID-19 were associated with a specific elevation of platelet α-granule proteins in the plasma and showed a positive correlation with markers for inflammation and tissue damage, suggesting a functionality of these antibodies in patients. The demonstration of functional and structural similarities between certain RBD-specific antibodies in patients with COVID-19 and pathogenic antibodies typical of HIT suggests a novel mechanism by which RBD-specific antibodies might contribute to thrombosis in COVID-19.

BATF regulates ILC2-mediated tissue repair and inflammation resolution during acute respiratory virus infection.

Significance While CD8 + T cells are essential for antitumor immunity, tumors often evade CD8 + T cell surveillance by immunosuppression. Recent study has shown that tumor-induced β-catenin activation in DCs suppresses CD8 + T cell immunity by inhibiting cross-priming, suggesting that activation of β-catenin in DCs might be a key mechanism tumors use to achieve immunosuppression. This report identified mTOR/IL-10 signaling as a previously unidentified mechanism for β-catenin–dependent inhibition of cross-priming. Surprisingly, our study also revealed that β-catenin in DCs was required for CD8 + T cell maintenance post-clonal expansion, suggesting that β-catenin exerts opposite functions during different stages of CD8 + T cell responses. Based on these findings, we have demonstrated selectively manipulating β-catenin signaling as a feasible strategy to improve DC vaccine efficacy.