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).