Immunomonitoring of Human Breast Milk Cells During HCMV-Reactivation

Frequencies of activated T cell populations increase in breast milk of HCMV-seropositive mothers during local HCMV reactivation

Background

Human cytomegalovirus (HCMV) can reactivate in the mammary gland during lactation and is shed into breast milk of nearly every HCMV-IgG-seropositive mother of a preterm infant. Dynamics of breast milk leukocytes during lactation, as well as blood leukocytes and the comparison between both in the context of HCMV reactivation is not well understood.

Methods

Here, we present the BlooMil study that aimed at comparing changes of immune cells in blood and breast milk from HCMV-seropositive- vs -seronegative mothers, collected at four time ranges up to two months post-partum. Viral load was monitored by qPCR and nested PCR. Multiparameter flow cytometry was used to identify leukocyte subsets.

Results

CD3+ T cell frequencies were found to increase rapidly in HCMV-seropositive mothers' milk, while they remained unchanged in matched blood samples, and in both blood and breast milk of HCMV-seronegatives. The activation marker HLA-DR was more strongly expressed on CD4+ and CD8+ T cells in all breast milk samples than matched blood samples, but HCMV-seropositive mothers displayed a significant increase of HLA-DR+ CD4+ and HLA-DR+ CD8+ T cells during lactation. The CD4+/CD8+ T cell ratio was lower in breast milk of HCMV-seropositive mothers than in the blood. HCMV-specific CD8+ T cell frequencies (recognizing pp65 or IE1) were elevated in breast milk relative to blood, which might be due to clonal expansion of these cells during local HCMV reactivation. Breast milk contained very low frequencies of naïve T cells with no significant differences depending on serostatus.

Conclusion

Taken together, we conclude that the distribution of breast milk leukocyte populations is different from blood leukocytes and may contribute to the decrease of breast milk viral load in the late phase of HCMV reactivation in the mammary gland.

Human Cytomegalovirus in breast milk is associated with milk composition, the infant gut microbiome, and infant growth

Human cytomegalovirus (CMV) is a highly prevalent herpesvirus that is often transmitted to the neonate via breast milk. Postnatal CMV transmission can have negative health consequences for preterm and immunocompromised infants, but any effects on healthy term infants are thought to be benign. Furthermore, the impact of CMV on the composition of the hundreds of bioactive factors in human milk has not been tested. Here, we utilize a cohort of exclusively breastfeeding full term mother-infant pairs to test for differences in the milk transcriptome and metabolome associated with CMV, and the impact of CMV in breast milk on the infant gut microbiome and infant growth. We find upregulation of the indoleamine 2,3- dioxygenase (IDO) tryptophan-to-kynurenine metabolic pathway in CMV+ milk samples, and that CMV+ milk is associated with decreased Bifidobacterium in the infant gut. Our data indicate a complex relationship between milk CMV, milk kynurenine, and infant growth; with kynurenine positively correlated, and CMV viral load negatively correlated, with infant weight-for-length at 1 month of age. These results suggest CMV transmission, CMV-related changes in milk composition, or both may be modulators of full term infant development.

Milk Transmission of Mammalian Retroviruses

The transmission of viruses from one host to another typically occurs through horizontal or vertical pathways. The horizontal pathways include transmission amongst individuals, usually through bodily fluids or excretions, while vertical transmission transpires from mother to their offspring, either during pregnancy, childbirth, or breastfeeding. While there are more than 200 human pathogenic viruses to date, only a small number of them are known to be transmitted via breast milk, including cytomegalovirus (CMV), human immunodeficiency virus type 1 (HIV-1), and human T cell lymphotropic virus type 1 (HTLV-1), the latter two belonging to the family Retroviridae. Breast milk transmission is a common characteristic among mammalian retroviruses, but there is a lack of reports summarizing our knowledge regarding this route of transmission of mammalian retroviruses. Here, we provide an overview of the transmission of mammalian exogenous retroviruses with a focus on Orthoretrovirinae, and we highlight whether they have been described or suspected to be transmitted through breast milk, covering various species. We also elaborate on the production and composition of breast milk and discuss potential entry sites of exogenous mammalian retroviruses during oral transmission.

Lactation-associated macrophages exist in murine mammary tissue and human milk

Macrophages are involved in immune defense, organogenesis and tissue homeostasis. Macrophages contribute to the different phases of mammary gland remodeling during development, pregnancy and involution postlactation. Less is known about the dynamics of mammary gland macrophages in the lactation stage. Here, we describe a macrophage population present during lactation in mice. By multiparameter flow cytometry and single-cell RNA sequencing, we identified a lactation-induced CD11c⁺CX3CR1⁺Dectin-1⁺ macrophage population (liMac) that was distinct from the two resident F4/80^hi and F4/80^lo macrophage subsets present pregestationally. LiMacs were predominantly monocyte-derived and expanded by proliferation in situ concomitant with nursing. LiMacs developed independently of IL-34, but required CSF-1 signaling and were partly microbiota-dependent. Locally, they resided adjacent to the basal cells of the alveoli and extravasated into the milk. We found several macrophage subsets in human milk that resembled liMacs. Collectively, these findings reveal the emergence of unique macrophages in the mammary gland and milk during lactation.

[Effect of breastfeeding on immune function in infants with human cytomegalovirus infection]

OBJECTIVES

To study the effect of breastfeeding on immune function in infants with human cytomegalovirus (HCMV) infection.

METHODS

A retrospective analysis was performed on the medical data of 135 infants with HCMV infection who were admitted to Children's Hospital Affiliated to Zhengzhou University from January 2021 to May 2022, and all these infants received breastfeeding. According to the results of breast milk HCMV-DNA testing, the infants were divided into two groups: breast milk HCMV positive (n=78) and breast milk HCMV negative (n=57). According to the median breast milk HCMV-DNA load, the infants in the breast milk HCMV positive group were further divided into two subgroups: high viral load and low viral load (n=39 each). Related indicators were compared between the breast milk positive and negative HCMV groups and between the breast milk high viral load and low viral load subgroups, including the percentages of peripheral blood lymphocyte subsets (CD3⁺ T cells, CD3⁺CD4⁺ T cells, CD3⁺CD8⁺ T cells, and CD19⁺ B cells), CD4⁺/CD8⁺ ratio, IgG, IgM, IgA, and urine HCMV-DNA load.

RESULTS

There were no significant differences in the percentages of CD3⁺ T cells, CD3⁺CD4⁺ T cells, CD3⁺CD8⁺ T cells, and CD19⁺ B cells, CD4⁺/CD8⁺ ratio, IgG, IgM, IgA, and urine HCMV-DNA load between the breast milk HCMV positive and HCMV negative groups, as well as between the breast milk high viral load and low viral load subgroups (P>0.05).

CONCLUSIONS

Breastfeeding with HCMV does not affect the immune function of infants with HCMV infection.

A cross-sectional study evidences regulations of leukocytes in the colostrum of mothers with obesity

BACKGROUND

Breastmilk is a dynamic fluid whose initial function is to provide the most adapted nutrition to the neonate. Additional attributes have been recently ascribed to breastmilk, with the evidence of a specific microbiota and the presence of various components of the immune system, such as cytokines and leukocytes. The composition of breastmilk varies through time, according to the health status of mother and child, and altogether contributes to the future health of the infant. Obesity is a rising condition worldwide that creates a state of systemic, chronic inflammation including leukocytosis. Here, we asked whether colostrum, the milk produced within the first 48 h post-partum, would contain a distinct leukocyte composition depending on the body mass index (BMI) of the mother.

METHODS

We collected peripheral blood and colostrum paired samples from obese (BMI > 30) and lean (BMI < 25) mothers within 48 h post-partum and applied a panel of 6 antibodies plus a viability marker to characterize 10 major leukocyte subpopulations using flow cytometry.

RESULTS

The size, internal complexity, and surface expression of CD45 and CD16 of multiple leukocyte subpopulations were selectively regulated between blood and colostrum irrespective of the study groups, suggesting a generalized cell-specific phenotype alteration. In obesity, the colostrum B lymphocyte compartment was significantly reduced, and CD16⁺ blood monocytes had an increased CD16 expression compared to the lean group.

CONCLUSIONS

This is the first characterization of major leukocyte subsets in colostrum of mothers suffering from obesity and the first report of colostrum leukocyte subpopulations in Latin America. We evidence various significant alterations of most leukocyte populations between blood and colostrum and demonstrate a decreased colostrum B lymphocyte fraction in obesity. This pioneering study is a stepping stone to further investigate active immunity in human breastmilk.

Human Breast Milk: From Food to Active Immune Response With Disease Protection in Infants and Mothers

Breastfeeding is associated with long-term wellbeing including low risks of infectious diseases and non-communicable diseases such as asthma, cancer, autoimmune diseases and obesity during childhood. In recent years, important advances have been made in understanding the human breast milk (HBM) composition. Breast milk components such as, non-immune and immune cells and bioactive molecules, namely, cytokines/chemokines, lipids, hormones, and enzymes reportedly play many roles in breastfed newborns and in mothers, by diseases protection and shaping the immune system of the newborn. Bioactive components in HBM are also involved in tolerance and appropriate inflammatory response of breastfed infants if necessary. This review summarizes the current literature on the relationship between mother and her infant through breast milk with regard to disease protection. We will shed some light on the mechanisms underlying the roles of breast milk components in the maintenance of health of both child and mother.