Human milk sIgA antibody in relation to maternal nutrition and infant vulnerability in northern Kenya

Maternal and infant predictors of proinflammatory milk immune activity in Kilimanjaro, Tanzania

OBJECTIVES

The immune system of milk (ISOM) creates a mother-infant immune axis that plays an important role in protecting infants against infectious disease (ID). Tradeoffs in the immune system suggest the potential for both protection and harm, so we conceive of two dimensions via which the ISOM impacts infants: promotion of protective activity and control of activity directed at benign targets. High variability in ISOM activity across mother-infant dyads suggests investment the ISOM may have evolved to be sensitive to maternal and/or infant characteristics. We assessed predictors of appropriate and misdirected proinflammatory ISOM activity in an environment of high ID risk, testing predictions drawn from life history theory and other evolutionary perspectives.

METHODS

We characterized milk in vitro interleukin-6 (IL-6) responses to Salmonella enterica (a target of protective immune activity; N = 96) and Escherichia coli (a benign target; N = 85) among mother-infant dyads in rural Kilimanjaro, Tanzania. We used ordered logistic regression and mixture models to evaluate maternal and infant characteristics as predictors of IL-6 responses.

RESULTS

In all models, IL-6 responses to S. enterica increased with maternal age and decreased with gravidity. In mixture models, IL-6 responses to E. coli declined with maternal age and increased with gravidity. No other considered variables were consistently associated with IL-6 responses.

CONCLUSIONS

The ISOM's capacities for appropriate proinflammatory activity and control of misdirected proinflammatory activity increases with maternal age and decreases with gravidity. These findings are consistent with the hypothesis that the mother-infant immune axis has evolved to respond to maternal life history characteristics.

Associations between milk cortisol and activity of the immune system of milk

OBJECTIVES

Both the immune system of human milk and milk cortisol have complex short- and long-term effects on child health and development. As understanding continues to grow of the independent effects of each of these components of milk, it is also important to investigate their intersection, including how milk cortisol affects the immune system of milk. We began this important endeavor through secondary analyses of archived milk specimens.

METHODS

Participants were 31 lactating mothers from upstate New York. We estimated milk cortisol concentrations via enzyme immunoassay. We assessed milk proinflammatory cytokine (interleukin-6, IL-6) responses to pathogenic (Salmonella) and commensal (Escherichia, Lactobacillus, Bifidobacterium) bacteria via in vitro stimulation. We estimated ordered logistic regression models to assess associations between milk cortisol and IL-6 responses to bacteria.

RESULTS

Milk cortisol ranged from 0.098 to 1.007 μg/dL. Milk cortisol was positively associated with IL-6 responses to S. enterica (B: 4.035; 95% CI: 0.674, 7.395) and B. breve (B: 3.675; 95% CI: 0.426, 6.924); this association persisted after controlling for child age. Results were less clear for associations between milk cortisol and IL-6 responses to L. acidophilus (B: 2.318; 95% CI: -1.224, 5.859) and E. coli (B: 2.366; 95% CI: -0.960, 5.692).

CONCLUSIONS

Complex interactions between cortisol and the immune system extend to milk. Milk cortisol was positively associated with proinflammatory responses to some bacteria in vitro. This may suggest that milk cortisol is causally upstream of protective immune activity.

Human milk immune factors, maternal nutritional status, and infant sex: The INSPIRE study

OBJECTIVES

Breastfeeding is an energetically costly and intense form of human parental investment, providing sole-source nutrition in early infancy and bioactive components, including immune factors. Given the energetic cost of lactation, milk factors may be subject to tradeoffs, and variation in concentrations have been explored utilizing the Trivers-Willard hypothesis. As human milk immune factors are critical to developing immune system and protect infants against pathogens, we tested whether concentrations of milk immune factors (IgA, IgM, IgG, EGF, TGFβ2, and IL-10) vary in response to infant sex and maternal condition (proxied by maternal diet diversity [DD] and body mass index [BMI]) as posited in the Trivers-Willard hypothesis and consider the application of the hypothesis to milk composition.

METHODS

We analyzed concentrations of immune factors in 358 milk samples collected from women residing in 10 international sites using linear mixed-effects models to test for an interaction between maternal condition, including population as a random effect and infant age and maternal age as fixed effects.

RESULTS

IgG concentrations were significantly lower in milk produced by women consuming diets with low diversity with male infants than those with female infants. No other significant associations were identified.

CONCLUSIONS

IgG concentrations were related to infant sex and maternal diet diversity, providing minimal support for the hypothesis. Given the lack of associations across other select immune factors, results suggest that the Trivers-Willard hypothesis may not be broadly applied to human milk immune factors as a measure of maternal investment, which are likely buffered against perturbations in maternal condition.

Does the immune system of milk increase activity for infants experiencing infectious disease episodes in Kilimanjaro, Tanzania?

INTRODUCTION

Multiple studies have reported that milk immune content increases for infants experiencing infectious disease (ID) episodes, suggesting that the immune system of milk (ISOM) offers enhanced protection when needed to combat ID.

METHODS

To test the hypothesis that ISOM content and/or activity increases during an infant's ID episode, we characterized milk secretory immunoglobulin A (sIgA; a major ISOM constituent) and in vitro interleukin-6 (IL-6) responses to Salmonella enterica and Escherichia coli, as system-level biomarkers of ISOM activity, in a prospective study among 96 mother-infant dyads in Kilimanjaro, Tanzania.

RESULTS

After control for covariates, no milk immune variables (sIgA, Coef: 0.03; 95% CI -0.25, 0.32; in vitro IL-6 response to S. enterica, Coef: 0.23; 95% CI: -0.67, 1.13; IL-6 response to E. coli, Coef: -0.11; 95% CI: -0.98, 0.77) were associated with prevalent ID (diagnosed at the initial participation visit). Among infants experiencing an incident ID (diagnosed subsequent to the initial participation), milk immune content and responses were not substantially higher or lower than the initial visit (sIgA, N: 61; p: 0.788; IL-6 response to S. enterica, N: 56; p: 0.896; IL-6 response to E. coli, N: 36; p: 0.683); this was unchanged by exclusion of infants with ID at the time of initial participation.

CONCLUSION

These findings are not consistent with the hypothesis that milk delivers enhanced immune protection when infants experience ID. In environments with a high burden of ID, dynamism may be less valuable to maternal reproductive success than stability in the ISOM.

Human milk lactoferrin variation in relation to maternal inflammation and iron deficiency in northern Kenya

BACKGROUND

Milk lactoferrin is a multi-functional, iron-binding glycoprotein with immunomodulatory effects, protecting infants against infectious diseases.

AIMS

This study explored how maternal inflammation/infection and iron-deficiency anemia (IDA) might influence human milk lactoferrin. Lactoferrin might be elevated with maternal inflammation resulting from infectious disease processes. Conversely, lactoferrin might decrease with IDA, corresponding to scarce maternal iron for transfer in milk. In these two hypothesized scenarios, the degree of lactoferrin elevation or decrease might vary with infant vulnerability to infectious diseases or malnutrition. Alternatively, lactoferrin might be unassociated with inflammation/infection or IDA if mothers could buffer it against these conditions.

MATERIALS & METHODS

We used cross-sectional data from Ariaal mothers of northern Kenya (n = 200) to evaluate associations between milk lactoferrin and maternal inflammation/infection, IDA, infant age/sex, and the mother-infant variable interactions in multivariate regression models.

RESULTS

Maternal inflammation was associated with higher lactoferrin for younger infants (<~5 months of age) but with lower lactoferrin for older infants. Maternal IDA was unassociated with lactoferrin alone or in interaction with infant variables.

DISCUSSION & CONCLUSION

Results suggest that mothers of vulnerable young infants deliver more lactoferrin when they have inflammation/infection but mothers with older infants do not, and that maternal delivery of lactoferrin is unaffected by their IDA. Longitudinal research should verify these findings.

Characterizing the extent human milk folate is buffered against maternal malnutrition and infection in drought‐stricken northern Kenya

Objectives

Folate is an essential nutrient fundamental to human growth and development. Human milk maintains high folate content across the maternal folate status range, suggesting buffering of milk folate with prioritized delivery to milk at the expense of maternal depletion. We investigated whether and how the extent of this buffering may diminish under prolonged nutritional and/or disease stress, while taking into consideration infants' varying vulnerability to malnutrition‐related morbidity/mortality.

Methods

A cross‐sectional study analyzed milk specimens from northern Kenyan mothers (n  = 203), surveyed during a historic drought and ensuing food shortage. Multiple regression models for folate receptor‐α (FOLR1) in milk were constructed. Predictors included maternal underweight (BMI < 18.5), iron‐deficiency anemia (hemoglobin <12 g/dl and dried‐blood‐spot transferrin receptor >5 mg/L), folate deficiency (hyperhomocysteinemia, homocysteine >12 or 14 μmol/L), inflammation (serum C‐reactive protein >5 mg/L), infant age and sex, and mother‐infant interactions.

Results

In adjusted models, milk FOLR1 was unassociated with maternal underweight, iron‐deficiency anemia and inflammation. FOLR1 was positively associated with maternal folate deficiency, and inversely associated with infant age. There was interaction between infant age and maternal underweight, and between infant sex and maternal folate deficiency, predicting complex changes in FOLR1.

Conclusions

Our results suggest that mothers buffer milk folate against their own nutritional stress even during a prolonged drought; however, the extent of this buffering may vary with infant age, and, among folate‐deficient mothers, with infant sex. Future research is needed to better understand this variability in maternal buffering of milk folate and how it relates to folate status in nursing infants.

Human mothers might have the capacity to buffer milk nutrient content against undue fluctuations under nutritional or disease stress. In the case of the micronutrient folate, this buffering is most apparent for younger infants.

DYNAMICS OF SIgA CONTENT IN BREAST MILK WHEN RISK FACTORS AND LACTATIONAL CHARACTERISTICS ARE CONSIDERED

The leading role associated with an anti-infective action of breast milk belongs to secretory IgA (SIgA). Therefore, the determination of the level of SIgA in colostrum and milk of mothers with different lactation levels and mothers at risk at different levels and duration of lactation has a practical interest. Aim. The research aims at studying the dynamics of SIgA content in breast milk, taking into account risk factors and features of lactation. Material and Methods. The content of SIgA in colostrum and breast milk of 372 mothers with full lactation and 208 with hypogalactia, of which 72 with early and 146 with late hypogalactia at different times of lactation (1-8 days and 1-3 months) was determined. The SIgA content was also studied in mothers; 65 with preeclampsia, including 12 with early hypogalactia, 24 with late hypogalactia, 23 with full lactation, and 44 with anemia of pregnancy, including 12 with early hypogalactia, 19 with late hypogalactia and 13 with full lactation. The determination of SIgA content in colostrum and milk was performed using the method of simple radial immunodiffusion in a gel by G. Mancini et al. Results and Discussion. The SIgA concentration in colostrum and breast milk decreased during the secretion process. In early hypogalactia, the content of SIgA did not differ significantly from the level of SIgA in colostrum and breast milk with full lactation in the early neonatal period and at 1-3 months of secretion. In the late hypogalactia, SIgA content did not differ significantly from its level in the control group. Due to the lower amount of milk received by the mother's child with hypogalactia, the supply of children with SIgA is insufficient, and the deficit is higher the sooner the hypogalactia develops. Similar changes in the dynamics of SIgA content have been found in mothers with preeclampsia and at different levels of lactation. The exception was the content of SIgA in colostrum and milk of mothers with anemia of pregnancy and early hypogalactia, which in the first five days of lactation was lower than in mothers with full lactation. Conclusion. The SIgA concentration in colostrum and breast milk decreases during the secretion process. The level of lactation does not affect the dynamics of SIgA content, except for the SIgA content in colostrum and breast milk of mothers with anemia of pregnancy and hypogalactia in the early stages of secretion. Despite the absence of a significant difference in SIgA levels in mothers with different levels of lactation due to less colostrum and milk received by children with early and late hypogalactia, the supply of SIgA is insufficient, and the cumulative deficit is higher the faster the hypogalactia develops.

Oropharyngeal administration of mother's own milk influences levels of salivary sIgA in preterm infants fed by gastric tube

The aim of the present study was to explore the effect of oropharyngeal mother’s milk administration on salivary secretory immunoglobulin A (sIgA) levels in preterm infants fed by gastric tube. Infants (n = 130) with birth weight < 1500 g were randomly allocated into two groups which both received breast milk for enteral nutrition. The experimental group (n = 65) accepted oropharyngeal mother’s milk administration before gastric tube feeding for 14 days after birth. The control group (n = 65) accepted oropharyngeal 0.9% normal saline administration. Saliva concentration of sIgA were assessed at the 2 h, 7th and 14th day after birth. The level of salivary sIgA in experimental group were significantly higher than those in control group on the 7th day after birth (p < 0.05), but there were no differences in salivary sIgA levels on the 14th day between the two groups. The results of quantile regression analysis showed that oropharyngeal mother’s milk administration, delivery mode and gestational age had significant effects on the increase of sIgA. SIgA in experimental group and the total number of intervention had a significant positive correlation (p < 0.05). Oropharyngeal mother’s milk administration can improve salivary sIgA levels of preterm infants.

Tradeoffs in milk immunity affect infant infectious disease risk

Background and objectives

The human immune system has evolved to balance protection against infection with control of immune-mediated damage and tolerance of commensal microbes. Such tradeoffs between protection and harm almost certainly extend to the immune system of milk.

Methodology

Among breastfeeding mother–infant dyads in Kilimanjaro, Tanzania, we characterized in vitro proinflammatory milk immune responses to Salmonella enterica (an infectious agent) and Escherichia coli (a benign target) as the increase in interleukin-6 after 24 h of incubation with each bacterium. We characterized incident infectious diseases among infants through passive monitoring. We used Cox proportional hazards models to describe associations between milk immune activity and infant infectious disease.

Results

Among infants, risk for respiratory infections declined with increasing milk in vitro proinflammatory response to S. enterica (hazard ratio [HR]: 0.68; 95% confidence interval [CI]: 0.54, 0.86; P: 0.001), while risk for gastrointestinal infections increased with increasing milk in vitro proinflammatory response to E. coli (HR: 1.44; 95% CI: 1.05, 1.99; P: 0.022). Milk proinflammatory responses to S. enterica and E. coli were positively correlated (Spearman’s rho: 0.60; P: 0.000).

Conclusions and implications

These findings demonstrate a tradeoff in milk immune activity: the benefits of appropriate proinflammatory activity come at the hazard of misdirected proinflammatory activity. This tradeoff is likely to affect infant health in complex ways, depending on prevailing infectious disease conditions. How mother–infant dyads optimize proinflammatory milk immune activity should be a central question in future ecological–evolutionary studies of the immune system of milk.

Impact of maternal antibodies and microbiota development on the immunogenicity of oral rotavirus vaccine in African, Indian, and European infants

Identifying risk factors for impaired oral rotavirus vaccine (ORV) efficacy in low-income countries may lead to improvements in vaccine design and delivery. In this prospective cohort study, we measure maternal rotavirus antibodies, environmental enteric dysfunction (EED), and bacterial gut microbiota development among infants receiving two doses of Rotarix in India (n = 307), Malawi (n = 119), and the UK (n = 60), using standardised methods across cohorts. We observe ORV shedding and seroconversion rates to be significantly lower in Malawi and India than the UK. Maternal rotavirus-specific antibodies in serum and breastmilk are negatively correlated with ORV response in India and Malawi, mediated partly by a reduction in ORV shedding. In the UK, ORV shedding is not inhibited despite comparable maternal antibody levels to the other cohorts. In both India and Malawi, increased microbiota diversity is negatively correlated with ORV immunogenicity, suggesting that high early-life microbial exposure may contribute to impaired vaccine efficacy.

In Vitro Stimulation of Whole Milk Specimens: A Field-Friendly Method to Assess Milk Immune Activity

BACKGROUND

The immune system of milk protects against infections and guides immune system development. A system-level understanding of milk immune activity is critical for research into infant infectious disease risk and lifelong health.

RESEARCH AIM

To describe a protocol to characterize immune activity in human milk via in vitro stimulation for use in population-based (rather than clinical) research.

METHODS

This study proceeded in two phases, each with a cross-sectional design. Human milk specimens were incubated for 24 hr at 37 °C in mammalian cell culture medium with stimuli (e.g., Salmonella enterica) in a CO₂-enriched environment. Immune responses to stimuli were characterized as the change in cytokine: [stimulated]/[baseline]. Predictors of cytokine responses were evaluated with generalized linear models.

RESULTS

Patterns were detectable across mother-child dyads: Interleukin-6 responses to stimuli were generally positively associated with child age and with maternal autoimmune disease.

CONCLUSIONS

Our method allows characterization of pro-inflammatory milk immune activity in vitro in population-based (rather than clinical) research settings. In vitro activity has a system-level interpretation and is likely to be of broad utility in global health research in settings with high infectious disease risk, where understanding the immune system of milk is critical to understanding maternal and child health.

The Breast Milk Immunoglobulinome

Breast milk components contribute to the infant’s immune development and protection, and among other immune factors, immunoglobulins (Igs) are the most studied. The presence of IgA in milk has been known for a long time; however, less information is available about the presence of other Igs such as IgM, IgG, and their subtypes (IgG1, IgG2, IgG3, and IgG4) or even IgE or IgD. The total Ig concentration and profile will change during the course of lactation; however, there is a great variability among studies due to several variables that limit establishing a clear pattern. In this context, the aim of this review was firstly to shed light on the Ig concentration in breast milk based on scientific evidence and secondly to study the main factors contributing to such variability. A search strategy provided only 75 studies with the prespecified eligibility criteria. The concentrations and proportions found have been established based on the intrinsic factors of the study—such as the sampling time and quantification technique—as well as participant-dependent factors, such as lifestyle and environment. All these factors contribute to the variability of the immunoglobulinome described in the literature and should be carefully addressed for further well-designed studies and data interpretation.

Cell-Mediated Immune Ontogeny Is Affected by Sex but Not Environmental Context in a Long-Lived Primate Species

Ecoimmunology conceptualizes the role of immunity in shaping life history in a natural context. Within ecoimmunology, macroimmunology is a framework that explains the effects of habitat and spatial differences on variation in immune phenotypes across populations. Within these frameworks, immune ontogeny—the development of the immune system across an individual life span—has received little attention. Here, we investigated how immune ontogeny from birth until adulthood is affected by age, sex, and developmental environment in a long-lived primate species, the bonobo. We found a progressive, significant decline of urinary neopterin levels, a marker for the cell-mediated immune response, from birth until 5 years of age in both sexes. The overall pattern of age-related neopterin changes was sex-specific, with males having higher urinary neopterin levels than females in the first 3 years of life, and females having higher levels than males between 6 and 8 years. Environmental condition (zoo-housed vs. wild) did not influence neopterin levels, nor did age-related changes in neopterin levels differ between environments. Our data suggest that the post-natal development of cell-mediated immune ontogeny is sex-specific but does not show plasticity in response to environmental conditions in this long-lived primate species. This indicates that cell-mediated immune ontogeny in the bonobo follows a stereotypic and maybe a genetically determined pattern that is not affected by environmental differences in pathogen exposure and energy availability, but that sex is an important, yet often overlooked factor shaping patterns of immune ontogeny. Investigating the causes and consequences of variation in immunity throughout life is critical for our understanding of life-history evolution and strategies, mechanisms of sexual selection, and population dynamics with respect to pathogen susceptibility. A general description of sex-specific immune ontogeny as done here is a crucial step in this direction, particularly when it is considered in the context of a species’ ecology and evolutionary history.

IgA and FcαRI: Versatile Players in Homeostasis, Infection, and Autoimmunity

Mucosal surfaces constitute the frontiers of the body and are the biggest barriers of our body for the outside world. Immunoglobulin A (IgA) is the most abundant antibody class present at these sites. It passively contributes to mucosal homeostasis via immune exclusion maintaining a tight balance between tolerating commensals and providing protection against pathogens. Once pathogens have succeeded in invading the epithelial barriers, IgA has an active role in host-pathogen defense by activating myeloid cells through divers receptors, including its Fc receptor, FcαRI (CD89). To evade elimination, several pathogens secrete proteins that interfere with either IgA neutralization or FcαRI-mediated immune responses, emphasizing the importance of IgA-FcαRI interactions in preventing infection. Depending on the IgA form, either anti- or pro-inflammatory responses can be induced. Moreover, the presence of excessive IgA immune complexes can result in continuous FcαRI-mediated activation of myeloid cells, potentially leading to severe tissue damage. On the one hand, enhancing pathogen-specific mucosal and systemic IgA by vaccination may increase protective immunity against infectious diseases. On the other hand, interfering with the IgA-FcαRI axis by monovalent targeting or blocking FcαRI may resolve IgA-induced inflammation and tissue damage. This review describes the multifaceted role of FcαRI as immune regulator between anti- and pro-inflammatory responses of IgA, and addresses potential novel therapeutic strategies that target FcαRI in disease.

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Cow, Goat, and Mare Milk Diets Differentially Modulated the Immune System and Gut Microbiota of Mice Colonized by Healthy Infant Feces

Studies on the possible alternative supplements to breastmilk are gaining research interests. Although milk from cow, goat, and mare is nutritious, its effects on the relationship between the immune system, metabolites, and gut microbiota remain unclear. This study aimed to comprehensively evaluate the effects of cow, goat, and mare milk on the immune system, metabolites, and gut microbiota of mice colonized by healthy infant feces using human milk as a standard. We examined the serum biochemistry parameters, immunity indicators, T cells, gut microbiota abundance, and metabolites. Results showed that the impact of human milk on alanine transaminase, glutamic oxaloacetic transaminase, total protein, globulin, and glucose values was different from the cow, goat, and mare milk types. The effects of mare milk on the percentage of CD4⁺ T, Th1, Th2, Th17, and Treg cells, and the levels of IL-2, IL-4, sIgA, and d-lactic acid in the serum of the human microbiota-associated mice were comparable to those of human milk. Also, bacterial 16S rRNA gene sequence analysis revealed that human milk enriched the relative abundance of Akkermansia and Bacteroides, cow milk increased the relative abundance of Lactobacillus, goat milk increased the relative abundance of Escherichia-Shigella, and mare milk improved the relative abundance of Klebsiella. Besides, mare milk was similar to human milk in the concentration of the metabolites we analyzed. Our findings suggest that mare milk can positively modulate the gut microbiota and immunity status of infants and thus could be a possible replacement for human milk.