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IntroductionInflammatory lesions after Influenza A viruses (IAV) are potential therapeutic target for which better understanding of post-infection immune mechanisms is required. Most studies to evaluate innate immune reactions induced by IAV are based on quantitative/functional methods and anatomical exploration is most often non-existent. We aimed to study pulmonary damage and macrophage recruitment using two-photon excitation microscopy (TPEM) after IAV infection.MethodsWe infected C57BL/6 CD11c+YFP mice with A/Puerto Ricco/8/34 H1N1. We performed immune cell analysis, including flow cytometry, cytokine concentration assays, and TPEM observations after staining with anti-F4/80 antibody coupled to BV421. We adapted live lung slice (LLS) method for ex-vivo intravital microscopy to analyze cell motility.ResultsTPEM provided complementary data to flow cytometry and cytokine assays by allowing observation of bronchial epithelium lesions and spreading of local infection. Addition of F4/80-BV421 staining allowed us to precisely determine timing of recruitment and pulmonary migration of macrophages. Ex-vivo LLS preserved cellular viability, allowing us to observe acceleration of macrophage motility.ConclusionAfter IAV infection, we were able to explore structural consequences and successive waves of innate immune cell recruitment. By combining microscopy, flow cytometry and chemokine measurements, we describe novel and precise scenario of innate immune response against IAV.

IntroductionCurrent approved COVID-19 vaccines, notably mRNA and adenoviral vectored technologies, still fail to fully protect against infection and transmission of various SARS-CoV-2 variants. The mucosal immunity at the upper respiratory tract represents the first line of defense against respiratory viruses such as SARS-CoV-2 and is thus critical to develop vaccine blocking human-to-human transmission.MethodsWe measured systemic and mucosal Immunoglobulin A (IgA) response in serum and saliva from 133 healthcare workers from Percy teaching military hospital following a mild infection (SARS-CoV-2 Wuhan strain, n=58) or not infected (n=75), and after SARS-CoV-2 vaccination (Vaxzevria®/Astrazeneca and/or Comirnaty®/Pfizer).ResultsWhile serum anti-SARS-CoV-2 Spike IgA response lasted up to 16 months post-infection, IgA response in saliva had mostly fallen to baseline level at 6 months post-infection. Vaccination could reactivate the mucosal response generated by prior infection, but failed to induce a significant mucosal IgA response by itself. Early post-COVID-19 serum anti-Spike-NTD IgA titer correlated with seroneutralization titers. Interestingly, its saliva counterpart positively correlated with persistent smell and taste disorders more than one year after mild COVID-19.DiscussionAs breakthrough infections have been correlated with IgA levels, other vaccine platforms inducing a better mucosal immunity are needed to control COVID-19 infection in the future. Our results encourage further studies to explore the prognosis potential of anti-Spike-NTD IgA in saliva at predicting persistent smell and taste disorders.

Here the authors generate a measles virus-based vaccine expressing SARSCoV-2 spike protein and show immunogenicity and protection in mice and hamsters, including neutralization of circulating variants of concerns in vitro.

Phospholipase D (PLD) hydrolyzes phosphatidylcholine into phosphatidic acid (PA), a lipidic mediator that may act directly on cellular proteins or may be metabolized into lysophosphatidic acid (LPA). We previously showed that PLD contributed to the mitogenic effect of endothelin-1 (ET-1) in a leiomyoma cell line (ELT3 cells). In this work, we tested the ability of exogenous PA and PLD from Streptomyces chromofuscus (scPLD) to reproduce the effect of endogenous PLD in ELT3 cells and the possibility that these agents acted through LPA formation. We found that PA, scPLD, and LPA stimulated thymidine incorporation. LPA and scPLD induced extracellular signal-regulated kinase (ERK1/2) mitogen-activated protein kinase activation. Using Ki16425, an LPA1/LPA3 receptor antagonist and small interfering RNA targeting LPA1 receptor, we demonstrated that scPLD acted through LPA production and LPA1 receptor activation. We found that scPLD induced LPA production by hydrolyzing lysophosphatidylcholine through its lysophospholipase D (lysoPLD) activity. Autotaxin (ATX), a naturally occurring lysoPLD, reproduced the effects of scPLD. By contrast, endogenous PLD stimulated by ET-1 failed to produce LPA. These results demonstrate that scPLD stimulated ELT3 cell proliferation by an LPA-dependent mechanism, different from that triggered by endogenous PLD. These data suggest that in vivo, an extracellular lysoPLD such as ATX may participate in leiomyoma growth through local LPA formation.