ABSTRACT
COVID-19 causes immune perturbations which may persist long-term, and patients frequently report ongoing symptoms for months after recovery. We assessed the extent and nature of immune activation at 3 months post hospital admission in patients with mild, moderate or severe COVID-19 and investigated whether immune activation associates with disease severity and long COVID. Patients with severe disease displayed persistent activation of CD4+ and CD8+ T-cells, based on expression of HLA-DR, CD38, Ki67 and granzyme B, but they lacked activation of other immune subsets. Elevated plasma levels of IL-4, IL-7, IL-17 and TNF- were present in patients with severe compared to mild and/or moderate disease. Plasma from severe patients caused T-cells from healthy donors to upregulate IL-15R, suggesting that factors in the plasma of severe patients may increase T-cell responsiveness to IL-15-driven bystander" activation, which may drive persistent T-cell activation after severe COVID-19. Patients with severe disease reported a higher number of long COVID symptoms which correlated with the frequency of two subsets of activated CD4+ and CD8+ T cells (CD4+ T-cell population 2 and CD8+ T-cell population 4; FDR p<0.05), however these associations were lost after adjusting for age, sex and disease severity. Our data suggests that persistent immune activation and long COVID correlate independently with severe disease.
ABSTRACT
Low-volume antibody assays can be used to track SARS-CoV-2 infection rates in settings where active testing for virus is limited and remote sampling is optimal. We developed 12 ELISAs detecting total or antibody isotypes to SARS-CoV-2 nucleocapsid, spike protein or its receptor binding domain (RBD), 3 anti-RBD isotype specific luciferase immunoprecipitation system (LIPS) assays and a novel Spike-RBD bridging LIPS total-antibody assay. We utilised pre-pandemic (n=984) and confirmed/suspected recent COVID-19 sera taken pre-vaccination rollout in 2020 (n=269). Assays measuring total antibody discriminated best between pre-pandemic and COVID-19 sera and were selected for diagnostic evaluation. In the blind evaluation, two of these assays (Spike Pan ELISA and Spike-RBD Bridging LIPS assay) demonstrated >97% specificity and >92% sensitivity for samples from COVID- 19 patients taken >21 days post symptom onset or PCR test. These assays offered better sensitivity for the detection of COVID-19 cases than a commercial assay which requires 100-fold larger serum volumes. This study demonstrates that low-volume in- house antibody assays can provide good diagnostic performance, and highlights the importance of using well-characterised samples and controls for all stages of assay development and evaluation. These cost-effective assays may be particularly useful for seroprevalence studies in low and middle-income countries.