IgG Fc Glycosylation Patterns of Preterm Infants Differ With Gestational Age

Abstract

Preterm infants acquire reduced amounts of Immunoglobulin G (IgG) via trans-placental transfer as compared to term infants which might explain their high susceptibility for infections. The reduced amount of IgG antibodies also results in a lower amount of anti-inflammatory Fc N-galactosylated and -sialylated IgG antibodies. This reduction or, even more, a qualitative shift in the type of IgG Fc glycosylation might contribute to the increased risk for sustained inflammatory diseases in preterm infants. It was the aim of our explorative study to investigate the IgG Fc glycosylation patterns in preterm infants of different gestational ages compared to term infants and mothers of preterm infants. In plasma samples of preterm infants (n = 38), we investigated IgG concentrations by use of ELISA. Furthermore, we analyzed IgG Fc glycosylation patterns in plasma of preterm infants (n = 86, 23-34 weeks of gestation), term infants (n = 15) and mothers from preterm infants (n = 41) using high performance liquid chromatography. Extremely low gestational age infants (born < 28 weeks of gestation during second trimester) had reduced IgG concentrations and decreased proportions of galactosylated (84.5 vs. 88.4%), sialylated (14.5 vs. 17.9%) and bisecting N-acetylglucosamine-containing (8.4 vs. 10.8%) IgG Fc N-linked glycans as compared to preterm infants born ≥28 weeks of gestation (during third trimester) and term infants. Increased non-galactosylated (agalactosylated, 16.9 vs. 10.6%) IgG Fc N-linked glycans were associated with the development of chronic inflammatory bronchopulmonary dysplasia (BPD). However, mothers of preterm infants born during second or third trimester of pregnancy did not show significant differences in IgG Fc glycosylation patterns. Thus, the IgG Fc glycosylation patterns of preterm infants depend on their gestational age. Although lack of bisecting N-acetylglucosamine has been associated with less inflammatory effector functions, the decreased IgG Fc galactosylation and sialylation with lower gestational age suggest a rather pro-inflammatory pattern. The difference in IgG Fc glycosylation patterns between preterm infants and mothers of preterm infants suggests a selective enrichment of IgG glyco forms in preterm infants, which might contribute to or result of the development of sustained inflammatory diseases like BPD.

Keywords: IgG Fc glycosylation; IgG antibodies; galactosylation; mothers; newborn; preterm infants; sialylation; trans-placental transfer.

Figure 1

IgG Fc N-glycan structure and representative chromatogram of IgG Fc N-glycans. (A) The glycan structure is composed of a biantennary core heptasaccharide comprised of N-acetylglucosamines (GlcNAc or GNAc, blue) and mannoses (Man, green). The core structure can be further modified by addition of fucose (Fuc), bisecting GlcNAc (GNAc, blue), galactose (G, yellow), or sialic acid (Neu5Ac, purple). (B) The different Fc N-glycan modifications G0, G0GNAc, G1, G1GNAc, G2, G2GNAc, G1S1, G2S1 and G2S2 (not marked in this sample analysis) were detected using hydrophilic interaction liquid chromatography (representative chromatogram), where glycans with higher hydrophobicity (e.g., more sugar units) were retained longer by the column. Glycan composition of collected fractions containing individual peaks was previously identified by MALDI-TOF analysis (38).

Figure 2

Plasma IgG concentrations were significantly decreased in preterm infants born at lower gestational ages. ELISA data for detection of human IgG-Fc parts. Intravenous immunoglobulin (IVIG) was used as a standard to estimate the plasma IgG concentration (mean ± SD, Mann-Whitney test). ^***p < 0.001.

Figure 3

IgG Fc glycosylation in preterm infants is dependent on gestational age. (A) IgG with agalactosylated Fc glycans were significantly increased, whereas (B) IgG with terminally galactosylated Fc glycans were unchanged and IgG with (C) sialylated and (D) bisecting Fc glycans were significantly decreased in preterm infants born < 28 weeks of gestational age. Term infants served as controls (mean ± SD, Kruskal-Wallis test). ^*p < 0.05, ^**p < 0.01, ^***p < 0.0001.

Figure 4

IgG Fc glycosylation patterns of preterm infants but not IgG Fc glycosylation of mothers of preterm infants correlate with gestational age of infants. (A) IgG with agalactosylated Fc glycans of preterm infants correlated negatively with gestational age, while Fc agalactosylation of mothers of preterm infants does not correlate with gestational age of their infants. (C) Sialylated and (D) bisecting Fc glycans correlated positively with gestational age of preterm infants which is not seen in Fc glycosylation of mothers from preterm infants. Terminal galactosylation (B) showed no correlation with gestational age in both preterm infants and mothers (Preterm infants: n = 86, mothers: n = 41, mother-infant-pairs: n = 20, Spearman correlation).

Figure 5

Agalactosylated IgG Fc N-glycans show a tendency to increase in preterm infants developing bronchopulmonary dysplasia (BPD). The correlation was done with (i) gender and clinical parameters defining, (ii) cause of birth, (iii) BPD, and (iv) sepsis (early and late onset sepsis cases included) for all preterm infant groups (mean ± SD, two-way ANOVA, multiple comparison within groups to adjust for gestational age). ^*p < 0.05.