Fig. 1: Complement regulatory proteins expression in PBMCs isolated from COVID-19 patients and healthy donors.

A Schematic representation of the experimental design for single cell RNA sequencing (scRNA-seq) analysis of PBMCs isolated from blood samples of donors with mild (n = 4), severe (n = 4), critical (n = 4) COVID-19 and healthy donors (n = 4). Study validation cohorts include 80 additional donors (n = 40 for flow cytometric analysis, n = 40 for Real-time PCR amplification) and six additional donors for the functional experiments (n = 3 for patient samples and n = 3 for healthy controls). B Major immune cell subsets were identified and visualised in 2D by UMAP. C UMAP representation of isolated PBMCs from healthy, mild, severe, and critical COVID-19 patients. D Stacked Bar charts showing the relative abundances (%) of cell clusters across disease states as indicated. E Expression levels of CD55, CD46, CD59 and CR1 in COVID-19 patients and controls. Mean expression bar plots, with error bars representing the 95% bootstrapped confidence intervals around the mean. Statistical analysis performed by the Wilcoxon rank sum test ****p < 0.0001, numbers next to asterisks indicate log fold changes. F Dot plot representing CD55 expression in healthy and COVID-19 patients of different states; the dot size represents the fraction of cells in the clusters, mean expression is colour coded as indicated. G Bar plots showing relative CD55 mRNA levels in whole blood samples isolated from severely and critically ill COVID-19 patients compared to healthy controls (mean ± SD). **p < 0.01, ***p < 0.001. Statistical analysis was performed by Kruskal–Wallis non-parametric test for more than two groups comparisons. Fisher’s least significant difference test was used for post-hoc analysis. H Receiver operating curve analysis for prediction of ICU admission by CD55 mRNA expression levels.