In utero activation of fetal memory T cells alters host regulatory gene expression and affects HIV susceptibility

Hyperparasitaemia during clinical malaria episodes in infants aged 0-24 months and its association with in utero exposure to Plasmodium falciparum

Objective

Existing information has shown that infants who are prenatally exposed to P. falciparum are susceptible to subsequent malaria infections. However, the effect of prenatal exposure to P. falciparum on parasite density during clinical malaria episodes has not been fully elucidated. This study is a component of a prospective cohort study for which initial results have been published. This component was designed to determine the effect of prenatal exposure to P. falciparum on parasite density during clinical malaria episodes in the first 24 months of life. A total of 215 infants were involved and monitored for clinical malaria episodes defined by fever (≥ 37 °C) and parasitaemia. The geometric mean parasite counts between exposed and unexposed infants were compared using independent samples t test. The effect of in utero exposure to P. falciparum on parasite density was assessed using binary logistic regression.

Results

The geometric mean parasite count per µl of blood during clinical malaria episodes in exposed infants was 24,889 (95% CI 18,286–31,490) while in unexposed infants it was 14,035 (95% CI 12,111–15,960), P < 0.05. Prenatal exposure to P. falciparum was associated with hyperparasitaemia during clinical malaria episodes (OR 7.04, 95% CI 2.31–21.74), while other factors were not significantly associated (P > 0.05).

Maternal HIV infection alters the immune balance in the mother and fetus; implications for pregnancy outcome and infant health

PURPOSE OF REVIEW

With the rapid roll-out of combination antiretroviral therapy to prevent mother-to-child transmission of HIV, there is an annual increase in the number of uninfected infants born to HIV-infected women. Although the introduction of combination antiretroviral therapy has vastly improved pregnancy outcome and the health of infants born to HIV-infected women, concerns remain regarding the impact the maternal HIV infection on the pregnancy outcome and the health of HIV-exposed uninfected infants.

RECENT FINDINGS

Maternal HIV infection is associated with negative pregnancy outcomes such as low birth weight. In addition, an increased susceptibility to infections is reported in HIV-exposed uninfected infants compared with infants born to uninfected women. Studies have shown that HIV-exposure affects the maternal/fetal unit, with increase of proinflammatory cytokine produced by placental cells, as well as altered infant immune responses. These changes could provide the underlying conditions for negative pregnancy outcomes and facilitate mother-to-child transmission of HIV in the infant. Further studies are required to understand the underlying mechanisms and investigate whether these altered infant immune responses persist and have clinical consequences beyond childhood.

SUMMARY

HIV infection in pregnant women is associated with altered immune responses in HIV-infected women and their offspring with clinical consequences for pregnancy outcome and the HIV-exposed uninfected infant. Further studies are required to address the origin and long-term consequences of prenatal HIV-exposure and subsequent immune activation for infant health.

Impact of HIV-1 infection on the feto-maternal crosstalk and consequences for pregnancy outcome and infant health

Adaptation of the maternal immune system to establish maternal/fetal equilibrium is required for a successful pregnancy. Viral infections, including HIV-1 infection, can alter this maternal/fetal equilibrium, with significant consequences for pregnancy outcome, including miscarriages, impaired fetal growth, and premature delivery. Furthermore, maternal HIV-1 infection has been shown to have a long-term impact on the developing fetal immune system also when the infant is not infected with the virus. In this review, we discuss the consequences of maternal HIV-1 infection and antiretroviral therapy on pregnancy outcome and the health of the uninfected HIV-1-exposed infant.

Cytomegalovirus upregulates expression of CCR5 in central memory cord blood mononuclear cells, which may facilitate in utero HIV type 1 transmission

Administration of combination antiretroviral therapy to human immunodeficiency virus type 1 (HIV-1)-infected pregnant women significantly reduces vertical transmission. In contrast, maternal co-opportunistic infection with primary or reactivated cytomegalovirus (CMV) or other pathogens may facilitate in utero transmission of HIV-1 by activation of cord blood mononuclear cells (CBMCs). Here we examine the targets and mechanisms that affect fetal susceptibility to HIV-1 in utero. Using flow cytometry, we demonstrate that the fraction of CD4(+)CD45RO(+) and CD4(+)CCR5(+) CBMCs is minimal, which may account for the low level of in utero HIV-1 transmission. Unstimulated CD4(+) CBMCs that lack CCR5/CD45RO showed reduced levels of HIV-1 infection. However, upon in vitro stimulation with CMV, CBMCs undergo increased proliferation to upregulate the fraction of T central memory cells and expression of CCR5, which enhances susceptibility to HIV-1 infection in vitro. These data suggest that activation induced by CMV in vivo may alter CCR5 expression in CD4(+) T central memory cells to promote in utero transmission of HIV-1.

Effect of helminth-induced immunity on infections with microbial pathogens

Helminth infections are ubiquitous worldwide and can trigger potent immune responses that differ from and potentially antagonize host protective responses to microbial pathogens. In this Review we focus on the three main killers in infectious disease-AIDS, tuberculosis and malaria-and critically assesses whether helminths adversely influence host control of these diseases. We also discuss emerging concepts for how M2 macrophages and helminth-modulated dendritic cells can potentially influence the protective immune response to concurrent infections. Finally, we present evidence advocating for more efforts to determine how and to what extent helminths interfere with the successful control of specific concurrent coinfections.

Molecular mechanisms of HIV-1 infection in neonatal target cells

HIV-1-infected neonates and infants have a higher viral load and progress to symptomatic AIDS more rapidly than their own infected mothers, as well as other infected adults, with differences in clinical manifestations, recurrent bacterial infections and CNS disorders. Two major reasons have been attributed to this differential HIV pathogenesis and disease; the relative immaturity of the neonate’s immune system and it’s inability to contain the highly replicating and mutating HIV-1, and the more efficient replication of HIV-1 in neonatal cells than in adult target cells. In this context, it has been demonstrated that HIV-1 replicates more efficiently in neonatal (cord) blood monocytes/macrophages and T lymphocytes – including naive and memory T lymphocytes – compared with adult blood cells. We have also determined the mechanisms of the differential HIV-1 replication in cord versus adult blood monocytes/macrophages and T lymphocytes (naive and memory), finding that it was influenced at the level of HIV-1 gene expression. The increased HIV-1 gene expression in neonatal versus adult target cells was regulated by differential expression of host factors, transcription factors (NF-κB, E2F, HAT-1, TFIIE, Cdk9 and Cyclin T1), signal transducers (STAT3 and STAT5A) and cytokines (IL-1β, IL-6 and IL-10). We also showed that nuclear extracts from cord cells interacted with HIV-1 long terminal repeat cis-acting sequences, including NF-κB, NFAT, AP1 and NF-IL6, to a greater extent when compared with adult peripheral blood mononuclear cell nuclear extracts. Additionally, shRNA of retroviral origin for STAT3 and IL-6 downregulated both their own gene expression as well as that of HIV-1, indicating that these factors influenced the differential expression of HIV-1 genes in cord cells compared with adult cells. In addition, HIV-1 integration plays an important role in differential HIV-1 replication and gene expression in neonatal versus adult cells by integrating into more actively transcribed genes in neonates compared with adults. We characterized 468 HIV-1 integration sites within cord and adult blood T lymphocytes and monocytes/macrophages, including genes coding for cellular components, and those involved with maintenance of the intracellular environment, enzyme regulation, cellular metabolism, catalytic activity and cation transport, as well as several potential transcription factor binding sites at the sites of integration. Additionally, the genes at the integration sites, transcription factors and transcription binding sites were expressed at higher levels in cord than adult target cells. In summary, the increased HIV-1 gene expression and replication in neonatal target cells due to differential expression of host factors all contribute to an increased viral load and faster disease progression in neonates and infants when compared with similar situations in adult patients. Based on these findings, it may be possible to identify new viral and host targets for use in developing strategies for the treatment and prevention of HIV-1.