Investigations Into the Immunomodulatory Mechanisms of Human Milk Extracellular Vesicles on CD4+ T Cells

Abstract

From birth onwards, the adaptive immune system of the mucosal surfaces of human infants undergoes a massive increase in antigen exposure. To avoid its over-activation, human milk plays a major role in the establishment of mucosal immune tolerance. Milk Extracellular Vesicles (EVs) were recently hypothesized to contribute to such immunomodulation as they were shown to increase the stimulation threshold required for activation of CD4+ T helper cells. EVs are nanosized lipid-bilayered vesicles known to mediate intercellular communication. The exact mechanisms by which these EVs modulate T cell activation are unknown. However, the transient and reversible dynamics of this inhibition, and the results of a recent milk EV proteomic analysis suggest that the EV contains a ‘ready-to-act’ protein cargo which interferes with signaling pathways of T cell activation upon delivery. To investigate the potentially immunomodulatory nature of the milk EV protein cargo, an in-silico analysis of the proteome was performed to identify the candidates for further analysis. Additionally, a Jurkat reporter cell line was optimized to efficiently measure EV-mediated immunomodulation of three canonical pathways of T cell activation. This read-out system confirmed that milk EVs cause a two-fold reduction in TCR-derived pathways and a three-fold reduction in CD28-derived pathways. It also revealed that milk EVs from allergic donors are not able to inhibit CD4+ T cell activation as well as milk EVs from non-allergic donors. Overall, a better understanding of milk-EV mediated immunomodulation could greatly enhance medical advice on breastfeeding and prevent the plethora of illnesses associated with over-activation of immunity.