Pregnancy Induces a Steady-State Shift in Alveolar Macrophage M1/M2 Phenotype That Is Associated With a Heightened Severity of Influenza Virus Infection: Mechanistic Insight Using Mouse Models

Pathogenesis of viral infections during pregnancy

SUMMARYViral infections during pregnancy are associated with significant adverse perinatal and fetal outcomes. Pregnancy is a unique immunologic and physiologic state, which can influence control of virus replication, severity of disease, and vertical transmission. The placenta is the organ of the maternal-fetal interface and provides defense against microbial infection while supporting the semi-allogeneic fetus via tolerogenic immune responses. Some viruses, such as cytomegalovirus, Zika virus, and rubella virus, can breach these defenses, directly infecting the fetus and having long-lasting consequences. Even without direct placental infection, other viruses, including respiratory viruses like influenza viruses and severe acute respiratory syndrome coronavirus 2, still cause placental damage and inflammation. Concentrations of progesterone and estrogens rise during pregnancy and contribute to immunological adaptations, placentation, and placental development and play a pivotal role in creating a tolerogenic environment at the maternal-fetal interface. Animal models, including mice, nonhuman primates, rabbits, and guinea pigs, are instrumental for mechanistic insights into the pathogenesis of viral infections during pregnancy and identification of targetable treatments to improve health outcomes of pregnant individuals and offspring.

Suppression of progesterone by influenza A virus mediates adverse maternal and fetal outcomes in mice

Influenza A virus infection during pregnancy can cause adverse maternal and fetal outcomes but the mechanism responsible remains elusive. Infection of outbred mice with 2009 H1N1 at embryonic day (E) 10 resulted in significant maternal morbidity, placental tissue damage and inflammation, fetal growth restriction, and developmental delays that lasted through weaning. Restriction of pulmonary virus replication was not inhibited during pregnancy, but infected dams had suppressed circulating and placental progesterone (P4) concentrations that were caused by H1N1-induced upregulation of pulmonary cyclooxygenase (COX)-1-, but not COX-2-, dependent synthesis and secretion of prostaglandin (PG) F2α. Treatment with 17-α-hydroxyprogesterone caproate (17-OHPC), a synthetic progestin that is safe to use in pregnancy, ameliorated the adverse maternal and fetal outcomes from H1N1 infection and prevented placental cell death and inflammation. These findings highlight the therapeutic potential of progestin treatments for influenza during pregnancy.IMPORTANCEPregnant individuals are at risk of severe outcomes from both seasonal and pandemic influenza A viruses. Influenza infection during pregnancy is associated with adverse fetal outcomes at birth and adverse consequences for offspring into adulthood. When outbred dams, with semi-allogenic fetuses, were infected with 2009 H1N1, in addition to pulmonary virus replication, lung damage, and inflammation, the placenta showed evidence of transient cell death and inflammation that was mediated by increased activity along the arachidonic acid pathway leading to suppression of circulating progesterone. Placental damage and suppressed progesterone were associated with detrimental effects on perinatal growth and developmental delays in offspring. Treatment of H1N1-infected pregnant mice with 17-OHPC, a synthetic progestin treatment that is safe to use in pregnancy, prevented placental damage and inflammation and adverse fetal outcomes. This novel therapeutic option for the treatment of influenza during pregnancy should be explored clinically.

Suppression of progesterone by influenza A virus mediates adverse maternal and fetal outcomes in mice

Influenza A virus infection during pregnancy can cause adverse maternal and fetal outcomes, but the mechanism responsible remains elusive. Infection of outbred mice with 2009 H1N1 at embryonic day (E) 10 resulted in significant maternal morbidity, placental tissue damage and inflammation, fetal growth restriction, and developmental delays that lasted through weaning. Restriction of pulmonary virus replication was not inhibited during pregnancy, but infected dams had suppressed circulating and placental progesterone (P4) concentrations that were caused by H1N1-induced upregulation of pulmonary cyclooxygenase (COX)-1, but not COX-2-, dependent synthesis and secretion of prostaglandin (PG) F2α. Treatment with 17-α-hydroxyprogesterone caproate (17-OHPC), a synthetic progestin that is safe to use in pregnancy, ameliorated the adverse maternal and fetal outcomes from H1N1 infection and prevented placental cell death and inflammation. These findings highlight the therapeutic potential of progestin treatments for influenza during pregnancy.

Diverse roles of lung macrophages in the immune response to influenza A virus

Influenza viruses are one of the major causes of human respiratory infections and the newly emerging and re-emerging strains of influenza virus are the cause of seasonal epidemics and occasional pandemics, resulting in a huge threat to global public health systems. As one of the early immune cells can rapidly recognize and respond to influenza viruses in the respiratory, lung macrophages play an important role in controlling the severity of influenza disease by limiting viral replication, modulating the local inflammatory response, and initiating subsequent adaptive immune responses. However, influenza virus reproduction in macrophages is both strain- and macrophage type-dependent, and ineffective replication of some viral strains in mouse macrophages has been observed. This review discusses the function of lung macrophages in influenza virus infection in order to better understand the pathogenesis of the influenza virus.

RIG-I agonist SLR10 promotes macrophage M1 polarization during influenza virus infection

Rationale

A family of short synthetic, triphosphorylated stem-loop RNAs (SLRs) have been designed to activate the retinoic-acid-inducible gene I (RIG-I) pathway and induce a potent interferon (IFN) response, which may have therapeutic potential. We investigated immune response modulation by SLR10. We addressed whether RIG-I pathway activation with SLR10 leads to protection of nonsmoking (NS) and cigarette smoke (CS)-exposed mice after influenza A virus (IAV) infection.

Methods

Mice were given 25 µg of SLR10 1 day before IAV infection. We compared the survival rates and host immune responses of NS and CS-exposed mice following challenge with IAV.

Results

SLR10 significantly decreased weight loss and increased survival rates in both NS and CS-exposed mice during IAV infection. SLR10 administration repaired the impaired proinflammatory response in CS-exposed mice without causing more lung injury in NS mice as assessed by physiologic measurements. Although histopathologic study revealed that SLR10 administration was likely to result in higher pathological scores than untreated groups in both NS and CS mice, this change was not enough to increase lung injury evaluated by lung-to-body weight ratio. Both qRT-PCR on lung tissues and multiplex immunoassay on bronchoalveolar lavage fluids (BALFs) showed that most IFNs and proinflammatory cytokines were expressed at lower levels in SLR10-treated NS mice than control-treaded NS mice at day 5 post infection (p.i.). Remarkably, proinflammatory cytokines IL-6, IL-12, and GM-CSF were increased in CS-exposed mice by SLR10 at day 5 p.i. Significantly, SLR10 elevated the ratio of the two chemokines (CXCL9 and CCL17) in BALFs, suggesting macrophages were polarized to classically activated (M1) status. In vitro testing also found that SLR10 not only stimulated human alveolar macrophage polarization to an M1 phenotype, but also reversed cigarette smoke extract (CSE)-induced M2 to M1 polarization.

Conclusions

Our data show that SLR10 administration in mice is protective for both NS and CS-exposed IAV-infected mice. Mechanistically, SLR10 treatment promoted M1 macrophage polarization in the lung during influenza infection. The protective effects by SLR10 may be a promising intervention for therapy for infections with viruses, particularly those with CS-enhanced susceptibility to adverse outcomes.

Biological Sex and Pregnancy Affect Influenza Pathogenesis and Vaccination

Males and females differ in the outcome of influenza A virus (IAV) infections, which depends significantly on age. During seasonal influenza epidemics, young children (< 5 years of age) and aged adults (65+ years of age) are at greatest risk for severe disease, and among these age groups, males tend to suffer a worse outcome from IAV infection than females. Following infection with pandemic strains of IAVs, females of reproductive ages (i.e., 15-49 years of age) experience a worse outcome than their male counterparts. Although females of reproductive ages experience worse outcomes from IAV infection, females typically have greater immune responses to influenza vaccination as compared with males. Among females of reproductive ages, pregnancy is one factor linked to an increased risk of severe outcome of influenza. Small animal models of influenza virus infection and vaccination illustrate that immune responses and repair of damaged tissue following IAV infection also differ between the sexes and impact the outcome of infection. There is growing evidence that sex steroid hormones, including estrogens, progesterone, and testosterone, directly impact immune responses during IAV infection and vaccination. Greater consideration of the combined effects of sex and age as biological variables in epidemiological, clinical, and animal studies of influenza pathogenesis is needed.

TcpC Inhibits M1 but Promotes M2 Macrophage Polarization via Regulation of the MAPK/NF-κB and Akt/STAT6 Pathways in Urinary Tract Infection

Abstract

TcpC is a multifunctional virulence factor of Uropathogenic Escherichia coli (UPEC). Macrophages can differentiate into two different subsets M1 and M2 that play distinct roles in anti-infection immunity. Here, we investigate the influence of TcpC on M1/M2 polarization and the potential mechanisms. Our data showed that M1 markers CD86 and iNOS were significantly inhibited, while the M2 markers CD163, CD206 and Arg-1 were enhanced in macrophages in kidneys from the TcpC-secreting wild-type CFT073 (CFT073^wt)-infected pyelonephritis mouse model, compared with those in macrophages in kidneys from TcpC knockout CFT073 mutant (CFT073^Δtcpc)-infected mice. CFT073^wt or recombinant TcpC (rTcpC) treatment inhibits LPS + IFN-γ-induced CD80, CD86, TNF-α and iNOS expression, but promotes IL-4-induced CD163, CD206, Arg-1 and IL-10 expression in both human and mouse macrophage cell lines THP-1 and J774A.1. Moreover, rTcpC significantly attenuated LPS + IFN-γ-induced phosphorylation of p38, ERK, p50 and p65 but enhanced IL-4-induced phosphorylation of Akt and STAT6. These data suggest that TcpC inhibits M1 but promotes M2 macrophage polarization by down-regulation of p38, ERK/NF-κB and up-regulation of the Akt/STAT6 signaling pathway, respectively. Our findings not only illuminate the regulatory effects of TcpC on macrophage M1/M2 polarization and its related signaling pathways, but also provide a novel mechanism underlying TcpC-mediated immune evasion of macrophage-mediated innate immunity.

Simple Summary

We investigate the influence of TcpC, a multifunctional virulence factor of Uropathogenic Escherichia coli (UPEC), on M1/M2 macrophage polarization and the potential mechanisms. TcpC-secreting wild-type CFT073 (CFT073^wt) or recombinant TcpC (rTcpC) treatment inhibits LPS + IFN-γ-induced CD80, CD86, TNF-α and iNOS expression, but promotes IL-4-induced CD163, CD206, Arg-1 and IL-10 expression in CFT073^wt-infected pyelonephritis model mouse and both human and mouse macrophage cell lines THP-1 and J774A.1, respectively. Moreover, rTcpC significantly attenuated LPS + IFN-γ-induced phosphorylation of p38, ERK, p50 and p65 but en-hanced IL-4-induced phosphorylation of Akt and STAT6. These data suggest that TcpC inhibits M1 but promotes M2 macrophage polarization by down-regulation of p38, ERK/NF-κB and up-regulation of the Akt/STAT6 signaling pathway, respectively. Our findings not only illuminate the regulatory effects of TcpC on macrophage M1/M2 polarization and its related signaling pathways, but also provide a novel mechanism underlying TcpC-mediated immune evasion of macrophage-mediated innate immunity.

Upregulated influenza A viral entry factors and enhanced interferon-alpha response in the nasal epithelium of pregnant rats

Despite the increased severity of influenza A infection in pregnancy, knowledge about the expression of cell entry factors for influenza A virus (IAV) and the innate immune response in the nasal epithelium, the primary portal of viral entry, is limited. Here, we compared the expression of IAV cell entry factors and the status of the innate immune response in the nasal epithelium of pregnant vs. non-pregnant female rats. IAV cell entry factors — sialic acid [SA] α-2,3- and α-2,6-linked glycans for avian and human IAV, respectively — were detected and quantified with lectin-based immunoblotting and flow cytometry. Baseline frequencies of innate immune cell phenotypes in single cell suspensions of the nasal epithelium were studied with flow cytometry. Subsequently, the magnitude of interferon and cytokine responses was studied with ELISA and cytokine arrays after intranasal resiquimod, a Toll-like receptor 7/8 agonist that mimics IAV infection. We noted substantially increased expression of cell entry factors for both avian and human IAV in the nasal epithelium during pregnancy. Assessment of the innate immune state of the nasal epithelium during pregnancy revealed two previously unreported features: (i) increased presence of tissue-resident plasmacytoid dendritic cells, and (ii) markedly enhanced release of interferon-α but not of the other interferons or cytokines 2 h after intranasal resiquimod. Collectively, our findings challenge the conventional notion of pregnancy-induced immunosuppression as a cause for severe influenza A disease and suggest the need for focused studies on viral tropism during pregnancy to better understand the proximate cause for the observed immunopathology.

System Complexity in Influenza Infection and Vaccination: Effects upon Excess Winter Mortality

Unexpected outcomes are usually associated with interventions in complex systems. Excess winter mortality (EWM) is a measure of the net effect of all competing forces operating each winter, including influenza(s) and non-influenza pathogens. In this study over 2400 data points from 97 countries are used to look at the net effect of influenza vaccination rates in the elderly aged 65+ against excess winter mortality (EWM) each year from the winter of 1980/81 through to 2019/20. The observed international net effect of influenza vaccination ranges from a 7.8% reduction in EWM estimated at 100% elderly vaccination for the winter of 1989/90 down to a 9.3% increase in EWM for the winter of 2018/19. The average was only a 0.3% reduction in EWM for a 100% vaccinated elderly population. Such outcomes do not contradict the known protective effect of influenza vaccination against influenza mortality per se—they merely indicate that multiple complex interactions lie behind the observed net effect against all-causes (including all pathogen causes) of winter mortality. This range from net benefit to net disbenefit is proposed to arise from system complexity which includes environmental conditions (weather, solar cycles), the antigenic distance between constantly emerging circulating influenza clades and the influenza vaccine makeup, vaccination timing, pathogen interference, and human immune diversity (including individual history of host-virus, host-antigen interactions and immunosenescence) all interacting to give the observed outcomes each year. We propose that a narrow focus on influenza vaccine effectiveness misses the far wider complexity of winter mortality. Influenza vaccines may need to be formulated in different ways, and perhaps administered over a shorter timeframe to avoid the unanticipated adverse net outcomes seen in around 40% of years.

Mediterranean Diet for the Prevention of Gestational Diabetes in the Covid-19 Era: Implications of Il-6 In Diabesity

The aim of this review is to highlight the influence of the Mediterranean Diet (MedDiet) on Gestational Diabetes Mellitus (GDM) and Gestational Weight Gain (GWG) during the COVID-19 pandemic era and the specific role of interleukin (IL)-6 in diabesity. It is known that diabetes, high body mass index, high glycated hemoglobin and raised serum IL-6 levels are predictive of poor outcomes in coronavirus disease 2019 (COVID-19). The immunopathological mechanisms of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection include rising levels of several cytokines and in particular IL-6. The latter is associated with hyperglycemia and insulin resistance and could be useful for predicting the development of GDM. Rich in omega-3 polyunsaturated fatty acids, vitamins, and minerals, MedDiet improves the immune system and could modulate IL-6, C reactive protein and Nuclear Factor (NF)-κB. Moreover, polyphenols could modulate microbiota composition, inhibit the NF-κB pathway, lower IL-6, and upregulate antioxidant enzymes. Finally, adhering to the MedDiet prior to and during pregnancy could have a protective effect, reducing GWG and the risk of GDM, as well as improving the immune response to viral infections such as COVID-19.

Innate Immune Responses to Acute Viral Infection During Pregnancy

Immunological adaptations in pregnancy allow maternal tolerance of the semi-allogeneic fetus but also increase maternal susceptibility to infection. At implantation, the endometrial stroma, glands, arteries and immune cells undergo anatomical and functional transformation to create the decidua, the specialized secretory endometrium of pregnancy. The maternal decidua and the invading fetal trophoblast constitute a dynamic junction that facilitates a complex immunological dialogue between the two. The decidual and peripheral immune systems together assume a pivotal role in regulating the critical balance between tolerance and defense against infection. Throughout pregnancy, this equilibrium is repeatedly subjected to microbial challenge. Acute viral infection in pregnancy is associated with a wide spectrum of adverse consequences for both mother and fetus. Vertical transmission from mother to fetus can cause developmental anomalies, growth restriction, preterm birth and stillbirth, while the mother is predisposed to heightened morbidity and maternal death. A rapid, effective response to invasive pathogens is therefore essential in order to avoid overwhelming maternal infection and consequent fetal compromise. This sentinel response is mediated by the innate immune system: a heritable, highly evolutionarily conserved system comprising physical barriers, antimicrobial peptides (AMP) and a variety of immune cells—principally neutrophils, macrophages, dendritic cells, and natural killer cells—which express pattern-receptors that detect invariant molecular signatures unique to pathogenic micro-organisms. Recognition of these signatures during acute infection triggers signaling cascades that enhance antimicrobial properties such as phagocytosis, secretion of pro-inflammatory cytokines and activation of the complement system. As well as coordinating the initial immune response, macrophages and dendritic cells present microbial antigens to lymphocytes, initiating and influencing the development of specific, long-lasting adaptive immunity. Despite extensive progress in unraveling the immunological adaptations of pregnancy, pregnant women remain particularly susceptible to certain acute viral infections and continue to experience mortality rates equivalent to those observed in pandemics several decades ago. Here, we focus specifically on the pregnancy-induced vulnerabilities in innate immunity that contribute to the disproportionately high maternal mortality observed in the following acute viral infections: Lassa fever, Ebola virus disease (EVD), dengue fever, hepatitis E, influenza, and novel coronavirus infections.

Impact of influenza virus during pregnancy: from disease severity to vaccine efficacy

Pregnant women are among the individuals at the highest risk for severe influenza virus infection. Infection of the mother during pregnancy increases the probability of adverse fetal outcomes such as small for gestational age, preterm birth and fetal death. Animal models of syngeneic and allogeneic mating can recapitulate the increased disease severity observed in pregnant women and are used to define the mechanism(s) of that increased severity. This review focuses on influenza A virus pathogenesis, the unique immunological landscape during pregnancy, the impact of maternal influenza virus infection on the fetus and the immune responses at the maternal–fetal interface. Finally, we summarize the importance of immunization and antiviral treatment in this population and highlight issues that warrant further investigation.

Diverse and Unexpected Roles of Human Monocytes/Macrophages in the Immune Response to Influenza Virus

Human monocytes/macrophages play a central role in the immune response and defense of the host from influenza virus infection. They classically act as antigen-presenting cells for lymphocytes in the context of an immune cell cluster. In that setting, however, monocytes/macrophages exhibit additional, unexpected, roles. They are required for influenza virus infection of the lymphocytes in the cluster, and they are responsible for lymphocyte apoptosis via their synthesis and expression of the viral neuraminidase. Surprisingly, human alveolar macrophages, expected to be among the first cells to encounter the virus, are not susceptible to direct infection by a human influenza virus but can be infected when the virus is complexed with an antibody. Such monocyte/macrophage responses to influenza virus challenge should be considered part of a very complex but quite effective defense, since the common outcome is recovery of the host with development of immunity to the challenging strain of virus.