Association of T-cell Immunity with IgG Serology
T-cell immunity to SARS-CoV-2 was generally associated with Spike-specific IgG responses11,12. Serum from SARS-CoV-2 patients were submitted for clinical nucleoprotein IgG titer. In 25 patients with nucleocapsid IgG positivity, we analyzed the association with CD4+ T-cell immunity to the 5 SARS-CoV-2 peptides (the highest response was compared). Although the T-cell immunity was not nucleocapsid-specific, there was a significant association between CD4+ T-cell immunity and nucleocapsid IgG titers (p=0.022; R= 0.457; Figure 2C).
We then examined Spike-specific IgG levels in 80 SARS-CoV2 infected patients and compared them to Spike-specific T-cell immunity. Here, 72.58% of patients with positive Spike-specific CD4+ T-cells had positive Spike-specific IgG levels. For patients with negative Spike-specific T-cell immunity, 61.11% also showed negative Spike-specific IgG levels. In 13 patients with high Spike-specific CD4+ T-cell immunity (IL-2+TNF-α+(%) in CD4+ > 0.3%), we also observed a correlation between T-cell immunity and level of Spike-specific IgG (p=0.0316; R=0.5288; Figure 2D). Therefore, T-cell immunity in SARS-CoV-2 patients, in general, was associated with positive IgG levels. However, 39% of previously infected patients with positive Spike-IgG antibodies did not demonstrate T-cell immunity. This may represent variability in the composition of immune responses from one individual to another as has been reported4-6.