Maternal and fetal complications during Influenza A virus infection
Creators: name: Oseghale, Osezua
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 320211
subject: Infectious diseases

description: Influenza A virus (IAV) infections during pregnancy have resulted in a considerable number of deaths and significant morbidity in the mother, with complications reported in the fetus, despite the lack of vertical transmission of IAV across the placenta. Pregnant women have an elevated risk of experiencing IAV-associated complications such as acute cardiopulmonary events, and acute respiratory distress syndrome (ARDS). Neonatal complications are also common with maternal infection and include fetal loss, preterm birth, fetal growth retardation/restriction (FGR) and neurological disorders. Although influenza-provokes an immune response in the mother that is detrimental to the fetus, the underlying mechanisms that drive the peri-natal complications remain elusive. Most studies addressing the impact of IAV in pregnancy have mainly focused on the IAV-induced immunological alterations. However, the link between IAV infection in the mother and fetal pathologies remained undefined. Perhaps, the reason for our lack of understanding could be because the impact of IAV infection on the cardiovascular adaptation occurring in pregnancy is yet to be elucidated. The cardiovascular adaptation functions to meet the nutrient and oxygen demands of the fetus, and is characterised by an increase in vasodilatation, cardiac output and decreases in total peripheral resistance. In cases where this adaptation is altered for example, in preeclampsia (PE), fetal pathologies are reported. Hence, the overall aim of my thesis was to investigate the effect of IAV infection in pregnancy on maternal vascular function and the downstream impact on fetal development.
 Accordingly, I investigated whether IAV infection promotes an innate and adaptive immune system response within the maternal vasculature and modifies vascular function. Here, I demonstrate that IAV infection in mice leads to a significant alteration in the maternal vascular landscape that underpins the maternal and downstream fetal pathology. In IAV infection of non-pregnant mice, the local lung inflammatory response was contained to the lungs and was self-resolving, whereas in pregnant mice, virus dissemination to major maternal blood vessels, including the aorta, resulted in a peripheral "vascular storm," with elevated pro-inflammatory and antiviral mediators and the influx of Ly6Clow patrolling monocytes and Ly6Chigh pro-inflammatory monocytes, neutrophils, and T cells. This vascular storm was associated with elevated levels of intracellular cell adhesion molecule (ICAM) and vascular cell adhesion molecule (VCAM) and the pattern-recognition receptors; toll like receptor (TLR) 7 and 9 in the vascular wall, resulting in profound vascular dysfunction. The sequalae of this IAV-driven vascular storm included placental growth retardation and intrauterine growth restriction, evidence of placental and fetal brain hypoxia, and increased circulating cell free fetal DNA (cffDNA) and soluble FMS-like Tyrosine kinase-1 (sFlt1). In contrast, IAV infection in non-pregnant mice caused no obvious alterations in endothelial function or vascular inflammation.

Upon establishing that IAV disseminates from the lung to the aorta during pregnancy to cause maternal vascular dysfunction through vascular inflammation and T cell activation, the aortic compartment most predisposed to IAV dissemination was next investigated. I specifically investigated the Peri Vascular Adipose Tissue (PVAT), which is known in hypertension-driven vascular dysfunction to be involved in the initiation of the vascular immune response. This led to a study investigating the contribution of the PVAT to maternal vascular storm and vascular dysfunction. Here I demonstrated that IAV disseminated into the PVAT of the aorta, as early as 6 h post infection (p.i), which preceded the significant impairment in endothelium-dependent relaxation to acetylcholine. Gene and protein expression analysis of IAV levels in the PVAT revealed a continuous increase through Days 1-3 post infection with the mRNA and protein levels being ~2 orders of magnitude greater compared with the vessel wall. IAV infection also increased Ly6Clow and Ly6Chigh monocytes in the vessel wall at 3 days p.i. which was then followed by a greater homing of these monocytes in the PVAT at Day 6 p.i. This vascular immune phenotype was characteristic of the vascular storm- like response, with increases in neutrophils, pro-inflammatory cytokines, and oxidative stress markers in the PVAT and vessel wall. IAV also triggered a PVAT compartmentalised elevation in CD4+ and CD8+ activated T cells.
The adaptive immune system within the aorta promotes vascular dysfunction and thereby the genesis of cardiovascular diseases (CVD) including hypertension and atherosclerosis. However, the regulation of the aortic T cell landscape is largely unknown. This led to a study investigating the development of an immunological pool of memory T cells in the aorta post-delivery and viral clearance. I demonstrated that IAV infection promotes a chronic alteration in T cell populations in the aorta during pregnancy. The aorta possessed low reservoirs of various T cell phenotypes including naïve CD4+ and CD8+ T cells, central memory T cells and effector memory T cells in the absence of infection. However, at 30 and 60 days post IAV, there was a significant elevation in these T cell phenotypes in the aorta, as well as an accumulation of IAV-specific CD8+ effector memory T cells. These aortic responses paralleled similar changes in T cell populations in the lung and mediastinal lymph nodes. Strikingly, the IAV infection caused significant impairment in the endothelium-dependent relaxation of the aorta for up to 60 days post-infection that was associated with higher levels of interferon-gamma (IFN-g).
These studies in mice provided fundamental mechanistic insight and a paradigm into how an immune response to a respiratory virus, such as IAV, is likely to specifically drive maternal and fetal pathologies during pregnancy. Moreover, this thesis serves as a basis to consider reviewing the therapeutic management of IAV infection in pregnancy. Rather than tackling the symptoms presented with antiviral drugs alone, perhaps treatment options for cardiovascular pathologies currently administered in pregnancy complications should be used in combination with antiviral drugs.