RESUMO
Objective:To investigate the antibody-dependent cell-mediated cytotoxicity (ADCC) in plasma samples from patients with SARS-CoV-2 infection and to evaluate its correlation with antibody titer and neutralizing activity.Methods:A simple method for ADCC detection was established using HEK293T cells expressing SARS-CoV-2 spike (S) protein as target cells and FcγRⅢa-V158-expressing Jurkat cells as effector cells. It was used to analyze the ADCC activity in 38 plasma samples after the ratio of effector cells to target cells was optimized. Plasma-specific antibody was detected by capturing ELISA, which was to capture the C-terminal-tagged recombinant SARS-CoV-2 S protein with an anti-tag antibody. The neutralizing activity in plasma samples was detected using a pseudovirus neutralization assay. Mann-Whitney U test was used for comparison between different groups and non-parametric Spearman correlation test was performed for correlation analysis. Results:The seroconversion rates for antibodies specific for S protein, S1 protein and RBD were all 97.4% (37/38), and the dynamic changes in antibody titers with recovery time showed that antibody titers peaked at 3-4 weeks. Among the plasma samples with neutralizing activity, those with antibody titers >1∶320 had stronger neutralizing activity than the plasma samples with antibody titers <1∶320 [IC 50: 749.6 (396.5-3 772.0) vs 81.4 (11.6-228.4), P<0.01]. ADCC activity was detectable in 86.8% (33/38) of the plasma samples, and its dynamic change with recovery time were consistent with that of specific antibody titer with a peak at 3-4 weeks. Correlation analysis showed ADCC was positively correlated with the titers of antibodies specific for S protein, S1 protein and RBD ( r=0.686, 0.535 and 0.471, all P<0.01). A positive correlation was also found between ADCC and neutralizing activity ( r=0.573, P<0.01). Conclusions:This study established a simple method for the detection of ADCC. Results of this study suggested that SARS-CoV-2 could induce specific ADCC in plasma and the ADCC might be associated with non-neutralizing antibodies. Besides, the activity of ADCC peaked at 3-4 weeks. These findings would be of reference value for clinical treatment with convalescent plasma.