Glycosylation Changes in Dairy Calf IGG Heavy Chains during Pre-Ruminant to Ruminant Transition: Pilot Study

Abstract Although IgG heavy chain glycans play a crucial role in mediating immunoglobulin G (IgG) effector functions, data on their structure in cattle remain limited. This study investigated whether pre-ruminant to ruminant transition in dairy calves is associated with changes in the expression of terminal galactose (Gal) and sialic acid (SA) on their IgG heavy chain glycans. The study was conducted using pooled serum samples from four groups of 20 calves, with median ages of 48±9, 75±7, 103±7, and 141±8 days (Group I, II, III, and IV, respectively). Gal and SA expression on affinity-isolated serum IgG heavy chains was analyzed by Ricinus communis agglutinin I (RCA I) and Sambucus nigra agglutinin (SNA) lectin blots. Gal and SA were expressed on IgG heavy chains of all age groups. The expression of Gal was highest in the youngest calves (Group I) and decreased by 40%, 53%, and 62% in Groups II, III, and IV, respectively. In contrast, SA expression was lowest in Group I, increased sharply in Group II (2.9 times higher than in Group I), remained stable in Group III, and slightly decreased in Group IV. The Gal-to-SA ratio in Group I was 5 to 6 times higher than in the older groups. This study highlights the dynamic changes in glycosylation of calf IgG molecules during preruminant to ruminant transition. Remains to be determined whether observed agedependent increase in SA expression might represent an adaptation to the evolving gastrointestinal microbiome in this period, when shifting toward sialylated, anti-inflammatory IgG that may help protect immature tissues from inflammatory damage.