T cells of exclusively breastfed neonates show reduced proliferation in response to stimulation by maternal cells
We performed mixed lymphocyte reactions (MLRs) on blood samples of 37 mother-and-baby dyads. Initially, maternal cells were stimulated with irradiated cord or neonatal cells and here we observed increased proliferation of CD3+ and CD4+ cells in response to neonatal peripheral blood mononuclear cells (PBMCs) at 3 weeks of age compared to birth (Supplementary Figure 2a). A similar increase (CD3+: 5.4 vs 15.5% median proliferating cells, CD4+: 5.3 vs 18% median proliferating cells) was observed when responder T cells of a non-pregnant healthy adult were used in combination with neonatal stimulator cells (Supplementary Figure 2b).
We next utilized cord and neonatal T cells in MLRs against irradiated maternal PBMCs (Figure 4a). Interestingly, here we observed decreased proliferation in neonatal CD3+ and CD8+, but not CD4+ cells in response to maternal stimulator cells at 3 weeks of age compared to birth (Figure 4b).
We further examined the influence of neonatal nutrition on these proliferative responses at 3 weeks of age. Sixteen neonates had been exclusively breastfed whereas 13 had received only formula and 8 had undergone a mixed milk intake. The decrease in the proliferation rate of CD3+ cells was still evident in exclusively breastfed neonates (60.7 vs 28.9% median proliferating cells) but was not present in the mixed feeding and exclusively formula-fed groups (Figure 4c). The same pattern was observed in CD4+ and CD8+ cells. Interestingly, the proliferation rate of CD3+, CD4+ and CD8+ cells of exclusively breastfed neonates was comparable at birth and at 3 weeks of age when PBMCs of a non-pregnant healthy adult were used as stimulators (n = 6), reflecting that the neonatal tolerance is specific to maternal antigens.