BTNL8 expression in whole blood. (A) Relative cellular abundances were estimated from whole blood RNA-seq data (whole blood transcriptomics cohort) using CibersortX. In the acute phase, MIS-C patients exhibit neutrophilia and lymphocytopenia, which gradually resolves. (B) BTNL8 expression (normalized counts) corrected for cell proportions. In the acute phase, the difference between MIS-C and viral cases survives correction. The small differences between MIS-C and healthy controls are further attenuated by the correction. (C)BTNL3 expression (normalized counts) corrected for cell proportions. (D–F) Gene expression of IFNG (D), BTNL8 (E), and BTNL3 (F) in whole blood in response to SARS-CoV-2 antigen (QuantiFERON RNA-seq cohort). Whole blood from acute and convalescent MIS-C patients and DV phenotypes compared with healthy controls following QuantiFERON assay. Individual with BTNL8 p.L101Q variant indicated by blue diamond. Statistical significance determined by one-way ANOVA (*P < 0.05; **P < 0.01; ****P < 0.0001).