SARS-CoV-2 anti-RBD and anti-N protein responses are differentially regulated between mother-child pairs: insight from a national study cohort at the Faroe Islands

Abstract

Background: Knowledge about SARS-CoV-2 antibody dynamics in neonates and direct comparisons with maternal antibody responses are not well established. This study aimed to characterize and directly compare the maternal and infant antibody response in a national birth cohort from the Faroe Islands.

Methods: The levels of immunoglobulins (Ig) targeting the receptor binding domain (RBD) of the spike protein and the nucleocapsid protein (N protein) of SARS-CoV-2 were investigated in maternal blood and umbilical cord blood from neonates. The study included 537 neonates and 565 mothers from the Faroe Islands, and follow-up samples were collected 12 months after birth. Multiple linear regression models were used to assess associations of maternal parameters with maternal and neonatal Ig levels and pregnancy outcomes.

Results: The finding showed that neonates acquired varying levels of SARS-CoV-2 antibodies through transplacental transfer, and the levels were significantly influenced by the mother's vaccination and infection status. The study also found that maternal vaccination and the presence of SARS-CoV-2 antibodies targeting spike RBD were associated with gestational age and APGAR scores. Furthermore, the anti-RBD and -N protein-specific antibody response dynamics during 12 months after birth exhibited differences between mothers and children. RBD and N protein responses were maintained at follow-up in the mother's cohort, while only the N protein response was maintained at follow-up in the children's cohort.

Conclusion: In conclusion, SARS-CoV-2-specific immune responses in newborns rely on maternal immunity, while the persistence of SARS-CoV-2-specific Igs appears to be differently regulated between mothers and children. The study provides new insights into the dynamics of SARS-CoV-2-specific immune responses in newborns and underscores the nuanced relationship between maternal factors and neonatal humoral responses.

Keywords: SARS-CoV-2; antibody duration; maternal immunization; nucleocapsid protein; spike protein.

Figure 1

Seroprevalence of SARS-CoV-2 anti-RBD and anti-N protein Ig. Levels of RBD- and N protein-specific Ig (bottom and top panel, respectively) over time in maternal serum at 32 weeks of pregnancy (left) and neonatal cord serum right after delivery (right). Circles and triangles represent the observed levels of circulating Ig antibodies in non-vaccinated and vaccinated mothers, respectively. Grey and yellow colors represent not infected and infected mothers, respectively. The horizontal black dotted line represents the threshold for positivity in each assay. Vertical dashed and dash-dotted lines indicate vaccine rollout and omicron breakout in the Faroe Islands, respectively. Data are represented in log10(OD) and the horizontal line represents the threshold for assay positivity.

Figure 2

Distribution of antibodies against RBD and N-protein in maternal and neonatal serum. Levels of RBD- and N protein-specific in maternal serum at 32 weeks of pregnancy (A, B) and neonatal cord serum right after delivery (C, D). Green and yellow colors represent not vaccinated and not vaccinated, respectively. Data reported as the median and interquartile range (box), whiskers represent 1.5 times the IQR. P-values were calculated using the Kruskal–Wallis test followed by multiple comparisons with Dunn’s correction. Spearman rank correlation of RBD and N protein Ig levels between maternal and neonatal serum, in groups of vaccinated (E, F) and infected individuals (G, H). Data are represented in log10(OD) and the horizontal line represents the threshold for assay positivity. P-values < 0.05 were considered statistically significant.

Figure 3

Persistence of RBD- and N-specific levels after 12 months. Levels of RBD- and N protein-specific Ig in maternal serum (top panel) and neonatal serum (bottom panel). Green and yellow colors represent baseline sampling and sampling at follow-up examination, respectively. Subdivided into groups based on maternal vaccination and/or infection during the period between baseline and follow-up sampling. Data reported as the median and interquartile range (box), whiskers represent 1.5 times the IQR. Data are represented in log10(OD) and the horizontal line represents the threshold for assay positivity. P-values < 0.05 were considered statistically significant by the Wilcoxon paired test.

Figure 4

Effect of breastfeeding on RBD- and N-specific levels. Levels of RBD- and N protein-specific Ig in neonatal serum at baseline sampling (green) and follow-up sampling (yellow). They were subdivided into groups based on the duration of breastfeeding (A, B) and whether a child is still breastfed or not (C, D). Data reported as the median and interquartile range (box), whiskers represent 1.5 times the IQR. Data are represented in log10(OD) and the horizontal line represents the threshold for assay positivity. P-values < 0.05 were considered statistically significant by the Wilcoxon paired test.

Figure 5

The variant specificity of the RBD-specific antibodies. A total of 36 sample pairs from mother and child collected at the 12-month follow-up (n=72) were analyzed in a direct setup detecting IgG antibodies against ancestral RBD (Wildtype) and two Omicron variants, B.1.1.529 RBD and BA.2 RBD (A, B). Data reported as the median and interquartile range (box), whiskers represent 1.5 times the IQR. Data are represented in log10(OD) and p-values < 0.05 were considered statistically significant by the Friedman test. Spearman rank correlation of RBD IgG levels between the variants was performed (C–H).