No abstract

The correlates of natural protective immunity to SARS-CoV-2 in the majority who experience asymptomatic infection or non-severe disease are not fully characterised, and remain important as new variants emerge. We addressed this question using blood transcriptomics, multiparameter flow cytometry and T cell receptor (TCR) sequencing spanning the time of incident infection. We identified a type 1 interferon (IFN) response common to other acute respiratory viruses, and a cell proliferation response that discriminated SARS-CoV-2 from other viruses. These responses peaked by the time the virus was first detected, and in some preceded virus detection. Cell proliferation was most evident in CD8 T cells and associated with rapid expansion of SARS-CoV-2 reactive TCRs. We found an equally rapid increase in immunoglobulin transcripts, but circulating virus-specific antibodies lagged by 1-2 weeks. Our data support a protective role for rapid induction of type 1 IFN and CD8 T cell responses to SARS-CoV-2.

Rationale: Persistent pulmonary sequelae are evident in many survivors of acute coronavirus disease 2019 (COVID-19) but the molecular mechanisms responsible are incompletely understood. Post-COVID radiological lung abnormalities comprise two broad categories, organising pneumonia and reticulation, interpreted as indicative of subacute inflammation and fibrosis, respectively. Whether these two patterns represent distinct pathologies, likely to require different treatment strategies is not known. Objectives: We sought to identify differences at molecular and cellular level, in the local immunopathology of post-COVID inflammation and fibrosis. Methods: We compared single-cell transcriptomic profiles and T cell receptor (TCR) repertoires of bronchoalveolar cells obtained from convalescent individuals with each radiological pattern of post-COVID lung disease (PCLD). Measurements and Main Results: Inflammatory and fibrotic PCLD single-cell transcriptomes closely resembled each other across all cell types. However, CD4 central memory T cells (TCM) and CD8 effector memory T cells (TEM) were significantly more abundant in inflammatory PCLD. A greater proportion of CD4 TCM also exhibited clonal expansion in inflammatory PCLD. High levels of clustering of similar TCRs from multiple donors was a striking feature of both PCLD phenotypes, consistent with tissue localised antigen-specific immune responses, but there was no enrichment for known SARS-CoV-2 reactive TCRs. Conclusions: There is no evidence that radiographic organising pneumonia and reticulation in PCLD are associated with differential immmunopathological pathways. Inflammatory radiology is characterised by greater bronchoalveolar T cell accumulation. Both groups show evidence of shared antigen-specific T cell responses, but the antigenic target for these T cells remains to be identified.