Saturday, May 16, 2015

Milk responds: Changes to milk immune factors with infant (or maternal) infection

FOREWARD. As many of you know, my recent research has been looking at milk composition, infant growth, and maternal health in a population of ethnic Tibetans living in the Himalayas of Nepal. The communities I work with were within 50 miles of the epicenter of the earthquake on April 25.  While the loss of life in these communities was minimal (thankfully), there was considerable destruction of homes, clinics, schools, and infrastructure (water, latrines). With the upcoming monsoon season, there is considerable need for safe drinking water, food storage, medical care, and safe homes. Several NGOs with long standing relationships with the communities are currently fundraising for relief and rebuilding efforts. Please consider donating to these organizations if you can afford to do so (NepalSEEDS; Tsum-Nubri Relief Center). We are still committed to these communities, and will continue to support infrastructure and research to promote maternal and child health.

In the last blog post – January – I discussed the idea of immunological memory in milk, particularly the well described association between maternal exposure to pathogenic bacteria in early life and the immunological memory of those bacteria, by specific forms of secretory Immunoglobulin-A (sIgA), many years later. Milk is incredibly dynamic, and this is certainly true for the immune factors in milk. Three recent papers have investigated this responsiveness in several samples, using a variety of immune factors to measure immune activation in milk.

Breakey et al., (2015) have articulated this as a model of two systems within the mammary gland – a protective paradigm, where some immune factors in milk are always protecting against infection; and the responsive paradigm, where active infection will increase the concentrations of immune factors in milk. Of the hundreds of known (and many unknown!) immune factors in milk, some will be generally protective, and others will be responsive (Brandtzaeg 2010). A few, including secretory IgA, will be both.  

Breakey et al., (2015) investigated the responsiveness of immune factors in milk to current infection using two biomarkers – sIgA and lactoferrin – in a sample of 29 Toba mother-infant dyads followed longitudinally. Both of these biomarkers have come up before (for reviews: sIgA; lactoferrin).The Toba are indigenous population from Argentina (Figure 1); previous generations have subsisted as foragers, but more recently the population has become increasingly concentrated in peri-urban areas, often in informal settlements lacking access to sanitation and water facilities. 
Figure 1: Location of the Toba. Image from wikicommons, author Nazareno98; produced in 2008.

Milk samples and interviews were collected monthly, allowing for the researchers to investigate milk composition before, during, and after an infection in the infant. Infant infections during the preceding month were collected during monthly interviews; all infants in the study had at least one illness over the course of the longitudinal study. Mothers did not report frequent illnesses, although this may have been underreporting. 

In this sample, infants receiving milk with higher sIgA were less likely to be ill, while infants receiving milk with more lactoferrin were more likely to be ill. Although causation cannot be certain, the authors hypothesize that lactoferrin content of milk increases during an infection (responsive) while sIgA levels are more generally protective. 

The study with the Toba follows two earlier studies of immune responsiveness in milk, both done in WEIRD populations. The earliest, by Riskin et al., (2012) remains one of my favorite papers. In this study, Riskin et al., recruited 51 mother-infant dyads, younger than 3 months, from Haifa, Israel into the study. 31 mother-infant pairs were hospitalized for fever at the time of recruitment, with an additional 20 pairs serving as healthy controls. Milk samples were collected from the mothers while the infants were hospitalized, and then seven days later; samples from controls were collected at one week intervals. Milk samples were analyzed for immune cells (lymphocytes, neutrophils, macrophages, CD45+), sIgA, lactoferrin, TNF-alpha, and IL-10 (Figure 2). 

Figure 2: Important cells in the immune system. Not all are found in milk. Image credit:
For the purposes of analyses, the participants were grouped into 3 categories: controls (healthy mom, healthy baby; n=20), all sick (all infants sick, moms sick or not; n=31), and sick infant (only baby sick; n=20). For the control group, there were no changes in the immune factors measured in milk from time 1 to time 2. However, for the sick group, there were significant declines in CD45+ cells, lymphocytes, neutrophils, macrophages, IL-10, and TNF-alpha. Lactoferrin and sIgA also declined, but the differences were minor. It does not appear that the associations were simply responding to maternal infection either. In the 20 mothers of sick infants who were not ill themselves, milk cd14+ cells, neutrophils, and macrophages also showed a significant decline from the original to the after measure. All other immune factors also showed declines, but again these were relatively minor. 

In an additional study of 21 mother-infant pairs, Hassiotou et al., (2013) reported increased leukocytes, and sIgA in the milk of mothers with infections compared to earlier and later samples from the same mothers collected as part of a longitudinal study design. While both maternal and infant infection increased leukocytes and sIgA in milk, this was most pronounced for mothers with breast infections. 

One of the leading hypotheses for how maternal physiology may respond to infection in the infant is through oral contact. Saliva from the infant’s mouth may enter the breast, carrying the pathogens responsible for the infection. This would encourage a localized immune response to the pathogen in the mammary gland itself (Hassiotou et al., 2013), although Riskin et al., (2012) also propose a model of subclinical infection in the mothers.

The capacity for milk to balance between innate and adaptive immune responses is incredibly important, especially for infants living in highly pathogenic, low resource environments such as the Toba, or my own participants from Nubri (more on this to come). Certainly, having a milk to gut superhighway for immune factors should be incredibly important in promoting gut integrity, decreasing infant illness, protecting against growth faltering, and promoting infant survival. Infant – or maternal – illness becomes then not a reason to stop nursing, but a reason to nurse more.

Brandtzaeg P. (2010) The mucosal immune system and its integration with the mammary glands. J Pediatr. 156(2 Suppl):S8-15

Breakey AA, Hinde K, Valeggia CR, Sinofsky A, Ellison PT. (2015) Illness in breastfeeding infants relates to concentration of lactoferrin and secretory Immunoglobulin A in mother's milk. Evol Med Public Health. 2015(1):21-31. doi: 10.1093/emph/eov002.

Hassiotou F, Hepworth AR, Metzger P, Tat Lai C, Trengove N, Hartmann PE, Filgueira L. (2013) Maternal and infant infections stimulate a rapid leukocyte response in breastmilk. Clin Transl Immunology. 2(4):e3. doi: 10.1038/cti.2013.1
Riskin A, Almog M, Peri R, Halasz K, Srugo I, Kessel A. (2012) Changes in immunomodulatory constituents of human milk in response to active infection in the nursing infant. Pediatr Res. 71(2):220-5. doi: 10.1038/pr.2011.34.