High-dimensional profiling reveals phenotypic heterogeneity and disease-specific alterations of granulocytes in COVID-19

Abstract

Since the outset of the COVID-19 pandemic, increasing evidence suggests that the innate immune responses play an important role in the disease development. A dysregulated inflammatory state has been proposed as a key driver of clinical complications in COVID-19, with a potential detrimental role of granulocytes. However, a comprehensive phenotypic description of circulating granulocytes in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)−infected patients is lacking. In this study, we used high-dimensional flow cytometry for granulocyte immunophenotyping in peripheral blood collected from COVID-19 patients during acute and convalescent phases. Severe COVID-19 was associated with increased levels of both mature and immature neutrophils, and decreased counts of eosinophils and basophils. Distinct immunotypes were evident in COVID-19 patients, with altered expression of several receptors involved in activation, adhesion, and migration of granulocytes (e.g., CD62L, CD11a/b, CD69, CD63, CXCR4). Paired sampling revealed recovery and phenotypic restoration of the granulocytic signature in the convalescent phase. The identified granulocyte immunotypes correlated with distinct sets of soluble inflammatory markers, supporting pathophysiologic relevance. Furthermore, clinical features, including multiorgan dysfunction and respiratory function, could be predicted using combined laboratory measurements and immunophenotyping. This study provides a comprehensive granulocyte characterization in COVID-19 and reveals specific immunotypes with potential predictive value for key clinical features associated with COVID-19.

SARS-CoV-2 Induces Cytokine Responses in Human Basophils

“…These data together indicate that resting human basophils undergo limited activation by SARS-CoV-2. Our data also suggest that higher expression of activation markers reported on basophils from COVID-19 patients was possibly not due to the direct virus stimulation (11).…”

“…Basophils play a major role in the pathogenesis of various respiratory diseases (8)(9)(10). Though the phenotype of basophils was previously analyzed in COVID-19 patients (11), it was not clear whether the activated basophil phenotype observed in the COVID-19 patients was due to direct virus stimulation or a repercussion of inflammatory responses. Therefore, to address this question, we first evaluated the response of basophils to SARS-CoV-2 infection.…”

“…Immuno-phenotyping studies have revealed that programmed death receptor ligand 1 (PD-L1, CD274, B7-H1; family of B7 costimulatory molecule) is dysregulated on monocytes, neutrophils, and T cells in COVID-19 patients (21). In addition, an enhanced expression of PD-L1 was also observed on the peripheral blood basophils of severe COVID-19 patients (11,(22)(23)(24), though this observation was not confirmed by another report (11). Therefore, we investigated the repercussion of SARS-CoV-2 infection on the expression of PD-L1 on the basophils at 24 h. We found that both resting as well as SARS-CoV-2-infected basophils lacked the expression of PD-L1 (Figure 4A).…”

COVID-19 Specific Immune Markers Revealed by Single Cell Phenotypic Profiling

“…Surprisingly we found that the expression of chemokine receptor CXCR4, which promotes hematopoiesis, cell migration/homing and bone marrow retention [ 51 ], was reduced in different immune subsets from COVID-19 patients of our considered cohort. Of interest, an altered expression of various receptors involved in migration, adhesion and activation, including CXCR4, CD63 and CD69, have been reported in COVID-19, highlighting specific immunophenotypes with predictive potential for clinical outcomes [ 52 , 53 ]. Furthermore, in contrast with an increase in both IFN-α and IFN-γ plasma levels, detected in the peripheral blood of COVID-19 patients at the onset of infection, a reduction in the expression of Interferon gamma receptor 1 (IFNGR1) in COVID-19-derived B cells and CD8+ naïve T cells was also detected, suggesting that the sensitivity of immune cells to inflammatory signal molecules might be lower during the infection and that an interferon-based treatment [ 54 ] may not be effective for all patients with mild to severe COVID-19.…”

IFN-γ Induces PD-L1 Expression in Primed Human Basophils

“…The pertinent role played by the basophils in the protection against helminth infections, and in the pathogenesis of asthma and other diseases is well documented [ 5 ]. More than ever, much interest is focused on understanding the role of various granulocytes in the immunopathology of various diseases, particularly diseases of the respiratory system, e.g., coronavirus disease (COVID-19) [ 6 ]. Several recent reports on COVID-19 have deciphered changes in the frequency of basophils, and surface molecules associated with their activation and degranulation [ 6 , 7 ].…”