Dynamics of innate and cognitive immune components in human milk during lactation

Abstract

Immunoglobulin A (IgA), immunoglobulin A1 (IgA1) and immunoglobulin A2 (IgA2) subclasses, κ and λ immunoglobulin light chains, C3 and C4 complement fractions, and Mannan Binding Lectin were assayed using nephelometric immunoassays in milk samples collected from 79 mothers during the first 12 weeks of lactation. The data obtained provide a precise description of the dynamics of immune proteins in human milk evolution over time and allow to depict four periods. In the early post-partum period (days 1–4), the high colostrum concentration of all immune proteins rapidly decreases. The IgA2 subclass, λ light chain, and C3 are more concentrated than IgA1, κ light chain and C4, respectively. The relative concentrations of C3 and C4 complement fractions are reversed during the following period (days 5–12). In a third stage extending from day 13 to day 44 post-partum, the levels of total IgA, IgA1, IgA2, κ, λ, C3, C4 and Mannan binding lectin (MBL) still slightly decrease or remain stable, but the respective ratios of immunoglobulin light chains and of IgA subclasses reverse consecutively. During the days 45–84 further and last period, an increase of IgA, of the IgA1/IgA2 ratio and of immunoglobulin light chains is noted, contrasting with stability or slight persistent decrease of C3, C4, and MBL concentrations. These data suggest that the concentrations of immune components in human milk are finely tuned during lactation, in a highly specific fashion, likely to best suit the newborn's need and properly protect the lactating mammary gland.