Immunoglobulin A N-glycosylation Presents Important Body Fluid-specific Variations in Lactating Mothers

Abstract

Secretory Immunoglobulin A (SIgA) is central to mucosal immunity: represents one of the main immunological mechanisms of defense against the potential attack of pathogens. During lactation SIgA is produced by plasmablasts in the mammary gland and is present in breast milk, playing a vital role in the passive immunity of the newborn. Interestingly, the different components of SIgA are highly N-glycosylated, and these N-Glycans have an essential role in health maintenance. In this work, we performed a glycomic study to compare N-glycosylation of SIgA purified from mature breast milk and saliva, and plasma IgA from the same lactating participants. Our results revealed a greater diversity than previously reported, with 89 glycan compositions that may correspond to over 250 structures. Among these glycans, 54 glycan compositions were characterized as body-fluid specific. Most of these unique N-Glycan compositions identified in SIgA from mature milk and IgA from plasma were fucosylated and both fucosylated and sialylated species, whereas in salivary SIgA the unique structures were mainly undecorated complex N-Glycans. In addition, we evaluated the effect of delivery mode on (S)IgA glycosylation. Lactating participants who had given birth by vaginal delivery presented an increased proportion of high mannose and fucosylated glycans in salivary SIgA, and selected high mannose, fucosylated, sialylated, and both fucosylated and sialylated glycans in plasma IgA, indicating that the hormonal changes during vaginal delivery could affect plasma and saliva IgA. These results reveal the structural details that provide a new dimension to the roles of (S)IgA N-Glycans in different tissues, and especially in maternal and new-born protection and infant development. The design of optimal recombinant IgA molecules specifically targeted to protect mucosal surfaces will need to include this dimension of structural detail.

Keywords: N-glycosylation; breast milk; chromatography; glycomics; immunoglobulin A; lactation; mass spectrometry; plasma or serum analysis; saliva.

Graphical abstract

Fig. 1.

A, Representative N-glycosylation profiles of SIgA obtained from mature milk and saliva, and plasma IgA from the same donor. High mannose glycans correspond to peaks in red. Complex and hybrid glycans without fucose or sialic acid were categorized as undecorated glycans (orange peaks); glycans containing fucose were selected as fucosylated glycans (green peaks); glycans with sialic acid were categorized as sialylated glycans (pink peaks); and glycans with both fucose and sialic acid were selected as fucosylated + sialylated glycans (blue peaks). B, Relative abundances of N-glycan groups in mature breast milk and saliva SIgA, and plasma IgA. Abundance for each glycan composition in all lactating participants was average to observed tissue-specific N-glycan variations.

Fig. 2.

N-glycan wheels of SIgA from (A) mature breast milk, (B) saliva, and IgA from (C) plasma are denoting individual relative abundances of N-Glycans identified in each tissue. High mannose, undecorated, fucosylated, sialylated, and fucosylated + sialylated glycans represented in shades of red, orange, green, pink and blue colors, respectively.

Fig. 3.

Effect of delivery mode on N-glycosylation of (A) salivary SIgA and (B) plasma IgA. Relative abundance of each IgA N-glycan was compared between cesarean delivery and vaginal delivery. Asterisks indicate the statistical significance in the two groups, p < 0.05. Numbers represent glycan compositions and each given value represents the number of each monosaccharide residue in the following order Hex-HexNAc-Fuc-NeuAc.

Fig. 4.

Comparison of high mannose glycans observed in plasma IgA of lactating participants according to the delivery mode and nonlactating participants. p < 0.05 is considered as statistically significant.