Neonatal immune tolerance promoted by breastfeeding is
mediated by regulatory T cells and is associated with a reduction in
release of inflammatory cytokines
Having observed that breastfeeding promotes the expansion of Tregs and
suppresses proliferative responses against maternal antigen, we next
investigated if this immune tolerance was dependent on the presence of
Tregs. To this end, we repeated the MLRs on a set of 6 mother-and-baby
dyads where babies were exclusively breastfed following the depletion of
CD25+ cells (Figure 5a). Pregnancy is associated with peripheral
accumulation of Tregs and the proliferation of maternal CD3+ cells in
response to neonatal antigens increased both at birth (20.4 vs 59.7%
median proliferating cells) and at 3 weeks of age (34.1 vs 57.1% median
proliferating cells) following depletion of CD25+ cells (Figure 5b). The
same pattern was observed for CD4+ but not in CD8+ cells. Of note, the
proliferation of neonatal CD3+ cells in response to maternal antigens
increased after depletion of CD25+ cells in samples taken at 3 weeks of
age (71.4 vs 85.1% median proliferating cells) but this was not seen
with the use of cord blood cells (Figure 5c). The same pattern was
observed for CD4+ but not in CD8+ cells.
We also measured the concentration of cytokines in MLR supernatants (n =
11) produced by neonatal T cells of exclusively breastfed neonates in
response to maternal antigens. The concentration of IFN-γ and TNF-α was
found to be lower at 3 weeks of age compared to birth, whereas no
difference was observed in case of the other cytokines tested (IL-4,
IL-6, IL-8, IL-10, IL-17). The maximal IFN-γ and TNF-α producing
capacity of neonatal T cells, tested by culturing with CD3/CD28
activator beads, was higher both at birth and at 3 weeks of age compared
to the level seen in response to maternal antigens at 3 weeks (Figure
5d). As such, breastfeeding is seen to suppress the inflammatory Th1
cytokine response of neonatal T cells in response to maternal antigen
stimulation.