2. Persistent SARS-CoV-2 reactive T cell response characterized by low avidity among the PASC subjects
In order to assess the contribution of SARS-CoV-2 S triggered persistent inflammation in PASC pathogenesis, we analyzed SARS-CoV-2 reactive T cell immunity. As the majority of the study participants were infected with either the WT or the alpha variant, we addressed the WT S reactive CD4+ and CD8+ T cell response. CD4+CD154+CD137+ and CD8+CD137+ T cells are defined as reactive CD4+ and CD8+ T cells, respectively. PASC subjects showed significantly higher frequencies of WT reactive CD4+ T cells compared to controls (Mann Whitney test p=0.008) (fig. 1A). WT reactive CD8+ T cell frequencies among the PASC study group were higher compared to controls, however, without statistical significance (fig. 1D).
As previously described and applied (22,24,25), we performed additionally an analysis of the functional avidity among reactive CD4+ and CD8+ T cells (gating strategy, fig. S1) using CD3low (high avidity) and CD3high (low avidity) expression as discrimination marker. We detected similar frequencies of WT reactive CD4+CD3low reactive T cells among PASC and controls (fig. 1B). However, the PASC study group presented higher frequencies of low avidity WT reactive CD4+CD3high T cells (Mann Whitney test p=0.003) (fig. 1C). Furthermore, we detected significantly higher frequencies of high avidity WT reactive CD8+CD3low T cells among the controls compared to PASC study group (Mann Whitney test p=0.007) (fig.1E), while low avidity WT reactive CD8+CD3high T cell frequencies were significantly higher among PASC subjects compared to controls (Mann Whitney test p=0.015) (fig.1F).
As next, we assessed the functionality of WT specific T cells regarding their cytokine production. PASC subjects showed significantly higher frequencies of WT reactive CD4 T cells producing TNFα compared to controls (Mann Whitney test p=0.016) (fig. 2B). Additionally, WT reactive CD8+ T cells producing IFNγ were significantly higher among the PASC study group (Mann Whitney test p=0.0045) (fig. 2G). Other subsets did not show any statistical difference in the cytokine-producing T cells (Fig. 2 A, C-F, H).