Maternal and infant infections stimulate a rapid leukocyte response in breastmilk

Abstract

Breastmilk protects infants against infections; however, specific responses of breastmilk immune factors to different infections of either the mother or the infant are not well understood. Here, we examined the baseline range of breastmilk leukocytes and immunomodulatory biomolecules in healthy mother/infant dyads and how they are influenced by infections of the dyad. Consistent with a greater immunological need in the early postpartum period, colostrum contained considerable numbers of leukocytes (13-70% out of total cells) and high levels of immunoglobulins and lactoferrin. Within the first 1-2 weeks postpartum, leukocyte numbers decreased significantly to a low baseline level in mature breastmilk (0-2%) (P<0.001). This baseline level was maintained throughout lactation unless the mother and/or her infant became infected, when leukocyte numbers significantly increased up to 94% leukocytes out of total cells (P<0.001). Upon recovery from the infection, baseline values were restored. The strong leukocyte response to infection was accompanied by a more variable humoral immune response. Exclusive breastfeeding was associated with a greater baseline level of leukocytes in mature breastmilk. Collectively, our results suggest a strong association between the health status of the mother/infant dyad and breastmilk leukocyte levels. This could be used as a diagnostic tool for assessment of the health status of the lactating breast as well as the breastfeeding mother and infant.

Keywords: breastfeeding; breastmilk; immune; immunoglobulin; infection; leukocyte.

Figure 1

Maternal and/or infant infections stimulate a breastmilk leukocyte response. (a) Reduction of CD45⁺ leukocyte numbers from colostrum to a low baseline level in transitional and mature breastmilk. A breastmilk CD45⁺ (green) leukocyte is shown; blue: nucleus; scale bar: 2.5 μm. (b–d) Effect of maternal or infant infections on breastmilk cells in selected examples (b), and in the overall study cohort (N=21) (c), and changes during lactation (d) (blue: healthy dyad; red: under infection). Local regression (loess) smoothers show the overall pattern in the data. In the mastitis example in b, the insert shows the leukocyte content of breastmilk collected on the same expression from the other non-mastitic breast.

Figure 2

Mastitis-specific breastmilk leukocyte subpopulations and properties. (a) Breastmilk collected from women with mastitis contained distinct leukocyte subpopulations, including monocytes, macrophages, T helper cells, cytotoxic T cells, NK (natural killer) cells and B cells. These cells responded to viral antigen and PHA stimulation in vitro via increased proliferation (b) and production of cytokines (c). *P<0.05, **P<0.01.

Figure 3

Maternal and/or infant infections stimulate a breastmilk humoral response. (a) Effect of maternal or infant infections on breastmilk biochemical content (sIgA, IgG, IgM and lactoferrin) in the overall study cohort (N=21). (b) Changes of the breastmilk biochemical content during lactation under healthy conditions (blue) and under infection (red). Local regression (loess) smoothers show the overall pattern in the data.

Figure 4

Interactions between breastmilk components in relation to specific infections, stage of lactation and exclusivity of breastfeeding. (a) Biplots illustrating the relationships between seven breastmilk immune markers as determined from a PCA. The first two components (PC1 and PC2) are shown in the top plot, and the second and third components (PC2 and PC3) are seen in the middle plot. The combination of these two plots provides a three-dimensional representation of the multivariate data. Dots illustrate the individual records, and the vectors indicate the relative weights of the markers on each of the principal components. Vector labels include: ‘Leukocyte': leukocytes per ml milk, ‘total cell': total cells per ml milk, ‘c': colostrum, ‘•': healthy, ‘M': mastitis, ‘R': recovering mastitis, ‘B': other breast conditions, ‘eye' and ‘ear': maternal eye and ear infections, respectively, ‘W': weaning, ‘P': periods, ‘T': vaginal thrush, ‘s': other infections of the mother or baby. Red lines show the relative weights of each of the measures on each of the components. (b) Effect of breastfeeding status (exclusive, non-exclusive) on milk leukocyte content under healthy and infection conditions.