Unravelling the effect of parity on immunoglobulins, cytokines and adipokines in human transitional milk and their association with infant infections during the first 6 months of life.

Abstract

Background: Human milk dynamically adapts its composition of immunoglobulins (Igs), cytokines, and other proteins as lactation progresses, influencing the infant's immune development and protection. Understanding how maternal factors, such as parity, influence the composition of human milk can provide strategies aimed at enhancing infant immune protection and reducing early-life infections. This study aims to investigate whether the immune composition of human milk differs based on parity, and if so, how these changes are related to infections in early life.

Methods: The study included 75 healthy mother-infant pairs from the MAMI cohort (Clinical Trial Registry NCT03552939), with milk samples collected from the same mothers at days 7 and 15 postpartum, during transitional lactation stage. Igs, cytokines, and adipokines were quantified using multiplex immunoassays and ELISA. A comparison was conducted between primiparous and multiparous mothers regarding both the overall and individual composition of immune components in human milk at each time point, as well as their evolution throughout the transitional phase.

Results: Infants from multiparous mothers recorded higher infection rates in early life than those of primiparous mothers. Some human milk immune components also differed by parity, with multiparous mothers exhibiting higher levels of IgA, total IgG, IgG1, IgG2, IgG3, IgE, and IL-23 at the beginning of the transitional phase (day 7), as well as higher IL-18 and IL-21 levels toward its end (day 15), compared to primiparous mothers. Additionally, the evolutionary pattern in levels of Igs, cytokines, and adipokines throughout the transitional milk stage also differed. Moreover, in multiparous mothers, higher levels of IgG, particularly IgG1 and IgG2 (day 7), as well as IL-18 and IL-22 (day 15), were associated with reduced infant infections, highlighting their potential protective role.

Conclusions: Parity is a maternal factor that influences some immune components of human milk during the transitional stage and may be linked to the susceptibility of infants to infections during the first 6 months of life. Future studies aimed at analyzing the impact of the parity factor, among others, on the progression of immune components in human milk may contribute to a better understanding and improved strategies for newborn health.