Functional and structural modifications of influenza antibodies during pregnancy

Pregnancy represents a unique tolerogenic immune state which may alter susceptibility to infection and vaccine-response. Here we characterized humoral immunity to seasonal influenza vaccine strains in pregnant and non-pregnant women. Pregnant women had reduced hemagglutinin subtype-1 (H1)-IgG, IgG1, and IgG2, hemagglutination inhibition and group 1 and 2 stem IgG. However, H1-specific avidity and FcγR1 binding increased. Influenza-antibodies in pregnancy had distinct Fc and Fab glycans characterized by di-galactosylation and di-sialylation. In contrast, agalactosylation and bisection were prominent outside of pregnancy. H1-specific Fc-functionality was moderately reduced in pregnancy, although likely compensated by stronger binding to cognate antigen and FcR. Multivariate analysis revealed distinct populations characterized by FcγR1 binding, H1-IgG levels, and glycosylation. Pooled sera from pregnant women exhibited longer retention in vivo . Our results demonstrate structural and functional modulation of humoral immunity during pregnancy in an antigen-specific manner towards reduced inflammation, increased retention in circulation, and efficient placental transport. ### Competing Interest Statement The authors have declared no competing interest.