Longitudinal Characterization of Phagocytic and Neutralization Functions of Anti-Spike Antibodies in Plasma of Patients after Severe Acute Respiratory Syndrome Coronavirus 2 Infection

Abstract

Phagocytic responses by effector cells to opsonized viruses have been recognized to play a key role in antiviral immunity. Limited data on coronavirus disease 2019 suggest that the role of Ab-dependent and -independent phagocytosis may contribute to the observed immunological and inflammatory responses; however, their development, duration, and role remain to be fully elucidated. In this study of 62 acute and convalescent patients, we found that patients with acute coronavirus disease 2019 can mount a phagocytic response to autologous plasma-opsonized Spike protein–coated microbeads as early as 10 d after symptom onset, while heat inactivation of this plasma caused 77–95% abrogation of the phagocytic response and preblocking of Fc receptors showed variable 18–60% inhibition. In convalescent patients, phagocytic response significantly correlated with anti-Spike IgG titers and older patients, while patients with severe disease had significantly higher phagocytosis and neutralization functions compared with patients with asymptomatic, mild, or moderate disease. A longitudinal subset of the convalescent patients over 12 mo showed an increase in plasma Ab affinity toward Spike Ag and preservation of phagocytic and neutralization functions, despite a decline in the anti-Spike IgG titers by >90%. Our data suggest that early phagocytosis is primarily driven by heat-liable components of the plasma, such as activated complements, while anti-Spike IgG titers account for the majority of observed phagocytosis at convalescence. Longitudinally, a significant increase in the affinity of the anti-Spike Abs was observed that correlated with the maintenance of both the phagocytic and neutralization functions, suggesting an improvement in the quality of the Abs.

Characterization of antibody‐dependent cellular phagocytosis in patients infected with hepatitis C virus with different clinical outcomes

“…It is noteworthy that although ADCP assay using antigen‐coated microbeads is a highly feasible and widely accepted surrogate in diverse infections that require access to high‐level Physical Containment laboratories (PC3) including Mycobacteria, 42 HIV, 43 SARS‐COV‐2, 44 and Influenza, 45 absence of live organisms in the assay system is a major limitation. Similarly, the use of recombinant HCV E2 for ELISA 46 and HCV E1E2 pseudovirus for neutralization, 47 are also well‐established surrogates of anti‐HCV antibody characterization.…”

“…The human hepatocyte cell line HuH‐7.5 with high CD81 expression obtained from Charles M. Rice, Rockefeller University, was infected with the GT1a or GT3a HCVpp and used to determine neutralizing activities of antibodies in the serum of patients infected with the corresponding viral genotype. The monocytic cell line THP‐1 (ATCC 202 TIB) was used as effector cells for Fc‐receptor mediated‐ADCP of patient plasma opsonized microbeads by flow cytometry as described 28 …”

“…Relevant assay controls included the acquisition of 2 × 10 4 events per tube from cells incubated with no beads and E2‐coated nonopsonized beads. The proportions of cells that phagocytosed the microbeads and mean fluorescence intensities (MFI) were analyzed using BD FlowJo version 10.5.0 software, and phagocytic scores (p‐score) were calculated as $$\left(\frac{ \% \,\mathrm{bead}\,\mathrm{positive}\,monocytes\times \mathrm{MFI}}{100}\right)\text{as}$$ previously described 28,61,66 . A positive p‐score was defined as three standard deviations above the background mean phagocytic score of healthy donors 61 .…”

“…previously described. 28,61,66 A positive p-score was defined as three standard deviations above the background mean phagocytic score of healthy donors. 61 A schematic diagram of the ADCP and representative data is shown in Figure 7.…”

“…Importantly, in patients with HIV infection, antibodies that neutralize broader HIV variants 22,23 also possess potent Fc receptor‐dependent effector functions, including ADCP, 24,25 and antibodies that maintain broadly neutralizing function at later stages of the disease showed an early and stronger Fc‐receptor‐dependent effector function 14,17,26,27 . A positive relationship between neutralization and ADCP was also observed in patients with severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) 15,28 and influenza virus 29 infections. However, the development, and role of ADCP in patients with HCV infection remain unknown.…”