In this review, we discuss the often overlooked tissue-resident fetal macrophages, Hofbauer cells, which are found within the chorionic villi of the human placenta. Hofbauer cells have been shown to have a phenotype associated with regulatory and anti-inflammatory functions. They are thought to play a crucial role in the regulation of pregnancy and in the maintenance of a homeostatic environment that is crucial for fetal development. Even though the numbers of these macrophages are some of the most abundant immune cells in the human placenta, which are sustained throughout pregnancy, there are very few studies that have identified their origin, their phenotype, and functions and why they are maintained throughout gestation. It is not yet understood how Hofbauer cells may change in function throughout normal pregnancy, and especially in those complicated by maternal gestational diabetes, preeclampsia, and viral infections, such as Zika, cytomegalovirus, and human immunodeficiency virus. We review what is known about the origin of these macrophages and explore how common complications of pregnancy dysregulate these cells leading to adverse birth outcomes in humans. Our synthesis sheds light on areas for human studies that can further define these innate regulatory cells.
HIV-1 viremia has been shown to induce several phenotypic and functional abnormalities in natural killer (NK) cells. To assess immune defects associated with HIV viremia, we examined NK cell function, differentiation status, and phenotypic alterations based on expression of inhibitory and activating receptors on NK cells in HIV-1 subtype C chronically infected participants from Durban, South Africa. NK cell phenotypic profiles were characterized by assessing sialic acid-binding immunoglobulin-like lectin-7 (Siglec-7), NKG2A, and NKG2C markers on frozen peripheral blood mononuclear cells from viremic, antiretroviral therapy (ART)-naive HIV-1 chronically infected participants (n = 23), HIV-1 chronically infected participants who had been on combination antiretroviral therapy (cART) for at least 12 months (n = 23) compared with healthy donors (n = 23). NK cell differentiation was assessed by measurement of killer immunoglobulin receptor (KIR) and NKG2A expression; CD57 and CD107a measurements were carried out in HIV viremic and healthy donors. All phenotypic and functional assessments were analyzed by using multicolor flow cytometry. HIV-1-infected participants displayed greater frequencies of the CD56CD16 (CD56negative) NK cell subset compared with healthy donors (p < .0001). Downregulation of Siglec-7 and NKG2A and upregulation of NKG2C were more pronounced in the CD56negative NK cell subset of viremic participants. The CD56negative subset demonstrated a differentiated (KIRNKG2A) phenotype with reduced CD57 expression and lower degranulation capacity in HIV-1-infected participants compared with healthy donors. HIV-1 infection induces the expansion of the CD56negative NK cell subset marked by altered receptor expression profiles that are indicative of impaired function and may explain the overall NK cell dysfunction observed in chronic HIV-1 infection.
Pre-pregnancy obesity is associated with several adverse maternal health outcomes, notably increased risk of infection as well as the incidence of gestational diabetes, preeclampsia, and preterm birth. However, the mechanisms by which pregravid obesity disrupts the pregnancy associated “immune clock” are still unknown. To address this question, we collected blood samples from women during the first and third trimesters and determined the impact of both pregnancy and pregravid obesity on circulating immune mediators, immune cell subset frequencies, and peripheral immune responses. While regardless of BMI, pregnancy was associated with an elevation in both Th1 and Th2 cytokines, pregravid obesity was associated with a dysregulation in circulating myeloid factors at term. Moreover, pregnancy in lean subjects was associated with enhanced monocyte activation, augmented chromatin accessibility at inflammatory loci, and heightened responses to LPS. Pregravid obesity disrupted this trajectory and was accompanied by a lack of transcriptional and epigenetic changes and alterations in metabolic status strongly suggesting a skewing towards immunotolerance. These findings provide novel insight into the increased susceptibility to infections observed with obesity during pregnancy.SUMMARYA healthy pregnancy is associated with progressive innate immune activation. Maternal factors such as obesity compromise this myeloid cell activation trajectory at genomic, epigenomic, functional, and metabolic levels, resulting in stagnant immune responses, suggestive of a state of tolerance.
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