Specific intracellular adhesion molecule-grabbing nonintegrin R1 is not involved in the murine antibody response to pneumococcal polysaccharides.

Streptococcus pneumoniae is a microorganism that frequently causes serious infections in children, the elderly, and immunocompromised patients. We studied whether the specific intracellular adhesion molecule-grabbing nonintegrin R1 (Sign-R1) receptor, involved in the uptake of capsular polysaccharides (caps-PS) by antigen-presenting cells, is necessary for the antibody response to pneumococcal caps-PS and phosphorylcholine (PC). The antibody response to caps-PS and PC was evaluated after vaccination with soluble caps-PS (Pneumovax) and after vaccination with heat-killed S. pneumoniae. The role of Sign-R1 was investigated by using Sign-R1 knockout mice and anti-Sign-R1 monoclonal antibodies. The immunoglobulin M (IgM) and IgG antibody response to PC and caps-PS (serotypes 3 and 14) was not affected by anti-Sign-R1 monoclonal antibodies. The IgM antibody response in Sign-R1 knockout mice was comparable to the antibody response in wild-type mice. The IgG antibody response to serotype 3, but not to serotype 14, tended to be lower in Sign-R1 knockout mice compared to wild-type mice. In conclusion, we found that Sign-R1 is not involved in the IgM antibody production to PC and caps-PS serotype 3 or 14 and the IgG immune response to PC and caps-PS serotype 14. There is no direct relation between capture and uptake of caps-PS serotype 14 by Sign-R1 and the initiation of the anti-caps-PS antibody production in mice.

ACE2 is the critical in vivo receptor for SARS-CoV-2 in a novel COVID-19 mouse model with TNF- and IFNγ-driven immunopathology

Despite tremendous progress in the understanding of COVID-19, mechanistic insight into immunological, disease-driving factors remains limited. We generated maVie16, a mouse-adapted SARS-CoV-2, by serial passaging of a human isolate. In silico modelling revealed how Spike mutations of maVie16 enhanced interaction with murine ACE2. MaVie16 induced profound pathology in BALB/c and C57BL/6 mice and the resulting mouse COVID-19 (mCOVID-19) replicated critical aspects of human disease, including early lymphopenia, pulmonary immune cell infiltration, pneumonia and specific adaptive immunity. Inhibition of the proinflammatory cytokines IFN{gamma} and TNF substantially reduced immunopathology. Importantly, genetic ACE2-deficiency completely prevented mCOVID-19 development. Finally, inhalation therapy with recombinant ACE2 fully protected mice from mCOVID-19, revealing a novel and efficient treatment. Thus, we here present maVie16 as a new tool to model COVID-19 for the discovery of new therapies and show that disease severity is determined by cytokine-driven immunopathology and critically dependent on ACE2 in vivo. Key pointsO_LIThe mouse-adapted SARS-CoV-2 strain maVie16 causes fatal disease in BALB/c mice and substantial inflammation, pneumonia and immunity in C57BL/6 mice C_LIO_LITNF/IFN{gamma} blockade ameliorates maVie16-induced immunopathology C_LIO_LIMaVie16 infection depends on ACE2 and soluble ACE2 inhalation can prevent disease C_LI