Breast milk induces the differentiation of monocytes into macrophages, promoting human cytomegalovirus infection

Human cytomegalovirus (HCMV) is a ubiquitous herpesvirus found in human breast milk that is frequently transmitted from HCMV-seropositive mothers to their infants during the postnatal period. Despite extensive research, the mechanisms underlying HCMV transmission from breast milk and the anatomical location at which virus transfer takes place remain unclear. Breast milk contains many uniquely differentiated macrophages that undergo specific morphological and functional modifications in the mammary gland during lactation. Although the existence of permissive HCMV infection in differentiated macrophages has been well-described, the role of breast milk in this process remains unknown. Herein, we report that exposure of isolated peripheral blood monocytes to breast milk induces their differentiation into macrophages that exhibit an M2 phenotype (CD14highCD163highCD68highCD206high) and promotes a productive and sustained HCMV infection. We also found that breast milk triggers macrophage proliferation and thus sustains a unique population of proliferating, long-lived, and HCMV-susceptible macrophages that are capable of ongoing production of infectious virions. These results suggest a mechanism that explains chronic HCMV shedding into the breast milk of postpartum seropositive mothers. We also found that HCMV virions released from breast milk-induced macrophages generate a productive infection in primary infant tonsil epithelial cells. Collectively, our results suggest that breast milk may facilitate HCMV transmission from mother to infant via the oropharyngeal mucosa.

IMPORTANCE

While human cytomegalovirus (HCMV) is frequently detected in the breast milk of HCMV-seropositive women and is often transmitted to infants via breastfeeding, the mechanisms by which this transmission occurs remain unclear. In this study, we modeled HCMV transmission at the oropharyngeal mucosa. We treated human monocytes with breast milk to mimic the lactating mammary gland microenvironment. We found that monocytes differentiated into macrophages with an M2 phenotype, which were highly permissive for HCMV. We also discovered that breast milk induces macrophage proliferation. Thus, exposure to breast milk increased the number of HCMV-susceptible macrophages and supported high levels of infectious HCMV. We found that HCMV virions released from breast milk-induced macrophages could infect primary infant tonsil epithelial cells. Collectively, these findings reveal the dual role of breast milk that induces the differentiation and proliferation of macrophages in the mammary gland and thus facilitates mother-to-child HCMV transmission at the oropharyngeal mucosa.

Concordance of Cytomegalovirus Saliva and Urine Testing in Infants for the Detection of Congenital Infection

Congenital cytomegalovirus is a leading cause of neurodevelopmental impairment and sensorineural hearing loss. We evaluated infants ≤21 days postnatal age who had both urine and saliva cytomegalovirus testing and determined concordance between the 2 tests and influence of very low birth weight on concordance. Discordance was low overall between urine and saliva testing; however, discordance was high in very low birth weight infants.

Salivary Glands and Viral Pathogenesis

The oral cavity is an epidemiologically relevant route of viral transmission due to the shedding of viruses in saliva. With advancements in salivary diagnostics, an increasing number of viruses have been detected. However, the anatomic source of virus in saliva is still largely unknown. Some viruses have a well-established tropism for the salivary glands (SGs), and recent studies have emphasized the importance of the glands as potential reservoirs for infectious viruses. Viral infections of the SGs have been linked to acute and chronic SG pathology and may be associated with SG dysfunction, with phenotypes similar to those seen in SjÖgren's disease (SjD), an autoimmune condition that affects the salivary and lacrimal glands. Understanding the breadth of viruses that infect the SG and the conserved or distinct host responses to these infections may provide insights into the pathogenesis of virus-mediated SG diseases. There is a need for further research to fully understand the molecular mechanisms by which viruses enter and replicate in the glands, their physiologic impact on SG function, and whether the SGs can serve as a long-term reservoir for infectious viral particles. The purpose of this review is to highlight a group of viruses that infect the salivary gland: hepatitis C virus, hepatitis D virus, severe acute respiratory syndrome coronavirus 2, enteric viruses, human T-cell leukemia virus type I, human immunodeficiency virus, human cytomegalovirus, and BK polyomavirus. We focus on the effects of viral infection on salivary gland (SG) inflammation, function, and its association with SjD.

Detection of Human Herpesviruses in Sera and Saliva of Asymptomatic HIV-Infected Individuals Using Multiplex RT-PCR DNA Microarray

Human herpesviruses (HHVs) are frequently linked to an increased risk of acquiring human immunodeficiency virus (HIV), and vice versa. This study aimed to detect human herpesvirus (HHV) members in the sera and saliva of asymptomatic HIV-infected individuals. Paired saliva and serum samples were obtained from 30 asymptomatic HIV-infected individuals. HHVs were detected with a multiplex reverse transcription-polymerase chain reaction (RT-PCR) DNA microarray Clart®Entherpex kit. A total of 30 subjects were enrolled: 23 (76.67%) men and 7 (23.33%) women. The present study showed that at least one or more HHV members were detected in the saliva and sera of all (100%) of the subjects. In the saliva, we detected herpes simplex virus 1 (HSV-1) 6.67%, herpes simplex virus 2 (HSV-2) 6.67%, Epstein-Barr virus (EBV) 86.67%, cytomegalovirus (CMV) 63.33%, HHV-6 (40%), and HHV-7 (83.33%). In the sera, HSV-2 (20%), EBV (30%), CMV (40%), HHV-6 (0%), and HHV-7 (76.67%) were found, but not HSV-1. VZV and HHV-8 were not detected in either the saliva or sera. EBV and HHV6 were significantly more prevalent in the saliva than they were in the sera of asymptomatic HIV-infected individuals (p < 0.05). However, no significant differences were found in the prevalence of HSV-1, EBV, CMV, HHV-6, and HHV-7 in the saliva and sera of asymptomatic HIV-infected individuals (p > 0.05). In conclusion, the multiplex RT-PCR DNA microarray can serve as a valuable diagnostic tool that can be used as a screening tool or a first-line test for HHVs infections.

Fetal Brain Damage in Human Fetuses with Congenital Cytomegalovirus Infection: Histological Features and Viral Tropism

Human cytomegalovirus (HCMV) causes congenital neurological lifelong disabilities. To date, the neuropathogenesis of brain injury related to congenital HCMV (cCMV) infection is poorly understood. This study evaluates the characteristics and pathogenetic mechanisms of encephalic damage in cCMV infection. Ten HCMV-infected human fetuses at 21 weeks of gestation were examined. Specifically, tissues from different brain areas were analyzed by: (i) immunohistochemistry (IHC) to detect HCMV-infected cell distribution, (ii) hematoxylin-eosin staining to evaluate histological damage and (iii) real-time PCR to quantify tissue viral load (HCMV-DNA). The differentiation stage of HCMV-infected neural/neuronal cells was assessed by double IHC to detect simultaneously HCMV-antigens and neural/neuronal markers: nestin (a marker of neural stem/progenitor cells), doublecortin (DCX, marker of cells committed to the neuronal lineage) and neuronal nuclei (NeuN, identifying mature neurons). HCMV-positive cells and viral DNA were found in the brain of 8/10 (80%) fetuses. For these cases, brain damage was classified as mild (n = 4, 50%), moderate (n = 3, 37.5%) and severe (n = 1, 12.5%) based on presence and frequency of pathological findings (necrosis, microglial nodules, microglial activation, astrocytosis, and vascular changes). The highest median HCMV-DNA level was found in the hippocampus (212 copies/5 ng of human DNA [hDNA], range: 10-7,505) as well as the highest mean HCMV-infected cell value (2.9 cells, range: 0-23), followed by that detected in subventricular zone (1.7 cells, range: 0-19). These findings suggested a preferential viral tropism for both neural stem/progenitor cells and neuronal committed cells, residing in these regions, confirmed by the expression of DCX and nestin in 94% and 63.3% of HCMV-positive cells, respectively. NeuN was not found among HCMV-positive cells and was nearly absent in the brain with severe damage, suggesting HCMV does not infect mature neurons and immature neural/neuronal cells do not differentiate into neurons. This could lead to known structural and functional brain defects from cCMV infection.

Virus-associated disruption of mucosal epithelial tight junctions and its role in viral transmission and spread

Oropharyngeal, airway, intestinal, and genital mucosal epithelia are the main portals of entry for the majority of human pathogenic viruses. To initiate systemic infection, viruses must first be transmitted across the mucosal epithelium and then spread across the body. However, mucosal epithelia have well-developed tight junctions, which have a strong barrier function that plays a critical role in preventing the spread and dissemination of viral pathogens. Viruses can overcome these barriers by disrupting the tight junctions of mucosal epithelia, which facilitate paracellular viral penetration and initiate systemic disease. Disruption of tight and adherens junctions may also release the sequestered viral receptors within the junctional areas, and liberation of hidden receptors may facilitate viral infection of mucosal epithelia. This review focuses on possible molecular mechanisms of virus-associated disruption of mucosal epithelial junctions and its role in transmucosal viral transmission and spread.

Virus-associated disruption of mucosal epithelial tight junctions and its role in viral transmission and spread

Oropharyngeal, airway, intestinal, and genital mucosal epithelia are the main portals of entry for the majority of human pathogenic viruses. To initiate systemic infection, viruses must first be transmitted across the mucosal epithelium and then spread across the body. However, mucosal epithelia have well-developed tight junctions, which have a strong barrier function that plays a critical role in preventing the spread and dissemination of viral pathogens. Viruses can overcome these barriers by disrupting the tight junctions of mucosal epithelia, which facilitate paracellular viral penetration and initiate systemic disease. Disruption of tight and adherens junctions may also release the sequestered viral receptors within the junctional areas, and liberation of hidden receptors may facilitate viral infection of mucosal epithelia. This review focuses on possible molecular mechanisms of virus-associated disruption of mucosal epithelial junctions and its role in transmucosal viral transmission and spread.

Histological Analysis of Term Placentas from Hyperimmune Globulin-Treated and Untreated Mothers with Primary Cytomegalovirus Infection

BACKGROUND

The Congenital Human Cytomegalovirus Infection Prevention (CHIP) study, a randomized, blinded, placebo-controlled trial, demonstrated that the efficacy of hyperimmune globulin (HIG) was not different from that of placebo regarding transmission of cytomegalovirus (CMV) from mothers to newborns. Our aim was to analyze histologically HIG effects on placentas collected for the CHIP study.

MATERIALS AND METHODS

Virological and histological analyses were performed on 40 placentas from transmitter and nontransmitter HIG-treated and untreated mothers by assessing the number of CMV-positive cells, tissue viral load, tissue damage, and compensatory mechanisms.

RESULTS

The HIG and placebo groups showed no significant differences in the number of CMV-positive cells (median number in 10 fields at 10 high-power fields: 2.5 vs. 2, p = 0.969) and viral load (median load: 5 copies/5 ng vs. 10.5 copies/5 ng, p = 0.874). Regarding histological examination, the scores of parameters related to tissue damage and hypoxic parenchymal compensation were higher in transmitters except for chorangiosis, with statistically significant differences observed for chronic villitis (p = 0.007), calcification (p = 0.011), and the total score of tissue damage (p < 0.001). The HIG and placebo groups showed no significant differences for all tissue damage and compensation parameters and overall scores.

DISCUSSION

HIGs are not able to reduce placental viral load and histological damage, which was significantly associated only with infection.