Fig. 6

Association between Fc-mediated effector functions and IgG4/IgG1 ratios or IgG avidity in older adults. The capacity of spike S1-specific serum antibodies to mediate ADNKA, ADCD and monocyte ADCP following mRNA vaccination in older adults (n = 38) at approximately 1 month after the third and fifth vaccinations relative to S1-specific total IgG levels at the same timepoint. Color scales indicate the IgG4/IgG1 ratio (A) or avidity index (B) of the SARS-CoV-2 spike S1-specific antibodies. Dotted lines indicate the level of the negative control (pre-pandemic serum sample). Solid grey lines were made using linear regression (straight lines) or locally estimated scatterplot smoothing (LOESS). SARS-CoV-2-infected individuals (based on N seropositivity) are indicated with open circles. ADCD, antibody-dependent complement deposition; ADCP, antibody-dependent cellular phagocytosis; ADNKA, antibody-dependent natural killer cell activation; BAU, binding antibody units; iMFI, integrated median fluorescence intensity; N, nucleoprotein