The stability of immunoglobulin a in human milk and saliva stored on filter paper at ambient temperature

Ecoimmunology in the field: Measuring multiple dimensions of immune function with minimally invasive, field-adapted techniques

OBJECTIVE

Immune function is multifaceted and characterizations based on single biomarkers may be uninformative or misleading, particularly when considered across ecological contexts. However, measuring the many facets of immunity in the field can be challenging, since many measures cannot be obtained on-site, necessitating sample preservation and transport. Here we assess state-of-the-art methods for measuring immunity, focusing on measures that require a minimal blood sample obtained from a finger prick, which can be: (1) dried on filter paper, (2) frozen in liquid nitrogen, or (3) stabilized with chemical reagents.

RESULTS

We review immune measures that can be obtained from point-of-care devices or from immunoassays of dried blood spots (DBSs), field methods for flow cytometry, the use of RNA or DNA sequencing and quantification, and the application of immune activation assays under field conditions.

CONCLUSIONS

Stable protein products, such as immunoglobulins and C-reactive protein are reliably measured in DBSs. Because less stable proteins, such as cytokines, may be problematic to measure even in fresh blood, mRNA from stabilized blood may provide a cleaner measure of cytokine and broader immune-related gene expression. Gene methylation assays or mRNA sequencing also allow for the quantification of many other parameters, including the inference of leukocyte subsets, though with less accuracy than with flow cytometry. Combining these techniques provides an improvement over single-marker studies, allowing for a more nuanced understanding of how social and ecological variables are linked to immune measures and disease risk in diverse populations and settings.

The effects of collection and storage conditions in the field on salivary testosterone, cortisol, and sIgA values

AIM

To determine if field-typical storage and collection conditions are related to salivary testosterone (T), cortisol (cort) and secretory immunoglobulin A (sIgA) as measured using commercially available kits.

SUBJECTS AND METHODS

This study assessed whether storage time (∼6 months to 1.5 years) at -35 °C impacted levels of the measured biomarkers (n = 10,247 samples). For a sub-set of T samples (n = 2954), we also evaluated the impact of collection conditions, such as time spent at room temperature in participants' homes (0-39 hours) and time spent in coolers (0.3-10 hours) in transit.

RESULTS

T was unrelated to storage and collection variables and there was no evidence of reduced sample fidelity at longer storage times. Cort samples stored at -35 °C for longer had significantly lower values, but the effect was small (β = -0.003 nmol/L/day, SE <0.001, p = 0.005). sIgA trended higher with longer storage at -35 °C (β = 0.84 µg/mL/day, SE = 0.45, p = 0.063). Collection and storage time variables did not improve the fit of any of the models except the one that evaluated cortisol.

CONCLUSIONS

Salivary T was unaffected by extended storage at -35 °C and only a weak relationship was found between storage time and salivary cort or sIgA. Findings underscore the robustness of these biomarkers under field-typical freezer storage conditions.

Milk immunity and reproductive status among Ariaal women of northern Kenya

Abstract Background: The immune factors in human milk protect infants from infection and promote immune development. Evidence suggests that the production of milk-specific immunoproteins is energetically costly, making them a form of maternal investment in offspring health that is subject to life history trade-offs.

AIM

This research tests the relationship between measures of reproductive effort and the production of milk immunoglobulin A (IgA) among Ariaal women, a settled northern Kenyan pastoralist population that experiences nutritional and disease stress.

SUBJECTS AND METHODS

Two hundred and forty-three lactating Ariaal women participated in a questionnaire, anthropometric measurement and milk collection. Milk IgA was analysed using ELISA.

RESULTS

There was a significant U-shaped relationship between post-partum months and milk IgA, reflecting decreasing investment in the current offspring over the early post-partum period and subsequent recovery of maternal energy status near the end. There was also a significant inverse U-shaped relationship between milk IgA and parity, with high parity women showing a drop in milk IgA. In contrast, anthropometric measures of energy status were not associated with the production of milk IgA.

CONCLUSION

This research shows that patterns of reproductive investment can be demonstrated in milk IgA in the absence of measured energy changes.

The effects of storage time and temperature on recovery of salivary secretory immunoglobulin A

OBJECTIVES

This study aimed to determine the optimal storage temperature to minimise degradation of salivary s-IgA for field-based surveillance applications in resource-limited settings.

METHODS

Saliva samples from 40 Zambian adults were stored at +25°C, +4°C, -20°C, and -80°C and each tested by ELISA for salivary s-IgA concentration at 0, 1, 2, 7, and 15 days. Differences were determined among concentrations over time and temperature compared with baseline values. Kruskal-Wallis tests were applied to analyse variance. Single and multivariate regression analyses estimated the influence of storage time and temperature on recoverable s-IgA.

RESULTS

Results revealed a statistically significant decrease in salivary s-IgA concentration as storage time increased and as temperature decreased. Degradation during storage time was most pronounced at lower temperatures.

CONCLUSIONS

s-IgA is stable at ambient temperatures in Zambia for at least 15 days, suggesting no need for cold chain handling before analysis in field-based surveillance applications.

Field and laboratory methods in human milk research

Human milk is a complex and variable fluid of increasing interest to human biologists who study nutrition and health. The collection and analysis of human milk poses many practical and ethical challenges to field workers, who must balance both appropriate methodology with the needs of participating mothers and infants and logistical challenges to collection and analysis. In this review, we address various collection methods, volume measurements, and ethical considerations and make recommendations for field researchers. We also review frequently used methods for the analysis of fat, protein, sugars/lactose, and specific biomarkers in human milk. Finally, we address new technologies in human milk research, the MIRIS Human Milk Analyzer and dried milk spots, which will improve the ability of human biologists and anthropologists to study human milk in field settings.

Brief communication: chronic undernutrition is associated with higher mucosal antibody levels among Ariaal infants of northern Kenya

The immune activation that occurs with infection diverts energy from growth and can contribute to poor nutritional outcomes in developing infants and children. This study investigates the association between salivary immunoglobulin A (IgA) levels and growth outcomes among Ariaal infants of northern Kenya. The Ariaal are a group of settled northern Kenyan pastoralists who are under considerable nutritional stress. Two hundred and thirty-nine breastfeeding Ariaal infants were recruited into the study and underwent anthropometric measurement and saliva collection, with mothers providing individual and household characteristics for them via questionnaire. Infant saliva samples were analyzed with an ELISA for IgA in the United States. Infant anthropometric measurements were converted to height-for-age z-scores (HAZ) using the WHO Child Growth Standards. Based on multivariate models performed in SAS 9.2 two main results emerge: 1) low HAZ, an indicator of chronic undernutrition, was significantly associated with higher IgA concentration (β = -0.12, P = 0.050) and 2) boys had significantly higher IgA levels than girls (β = 0.25, P = 0.039). Although there was not a significant interactive effect between HAZ and sex, the two variables confound each other, with boys having significantly lower HAZ values than girls do. In addition, maternal breastmilk IgA was significantly associated with infant salivary IgA, indicating that maternal effects play a role in infant IgA development. Future research will unravel the three-way association between sex, stunting, and immune function in the Ariaal community.