A new paper published in Cell by Charitè group opens new perspectives to complement role in Covid-19

Highlights

• •Severe COVID-19 is marked by activated, highly cytotoxic CD16⁺ T cells
• •Immune complex-mediated degranulation of CD16⁺ T cells causes endothelial cell injury
• •C3a-rich environment in severe COVID-19 promotes differentiation of CD16⁺ T cells
• •Activated CD16⁺ T cells and complement proteins are associated with fatal outcome

Summary

Severe COVID-19 is linked to both dysfunctional immune response and unrestrained immunopathology, and it remains unclear whether T cells contribute to disease pathology. Here, we combined single-cell transcriptomics and single-cell proteomics with mechanistic studies to assess pathogenic T cell functions and inducing signals. We identified highly activated, CD16⁺ T cells with increased cytotoxic functions in severe COVID-19. CD16 expression enabled immune complex-mediated, T cell receptor-independent degranulation and cytotoxicity not found in other diseases. CD16⁺ T cells from COVID-19 patients promoted microvascular endothelial cell injury and release of neutrophil and monocyte chemoattractants. CD16⁺ T cell clones persisted beyond acute disease maintaining their cytotoxic phenotype. Increased generation of C3a in severe COVID-19 induced activated CD16⁺ cytotoxic T cells. Proportions of activated CD16⁺ T cells and plasma levels of complement proteins upstream of C3a were associated with fatal outcome of COVID-19, supporting a pathological role of exacerbated cytotoxicity and complement activation in COVID-19.