BTNL8 and BTNL3 expression in patient whole blood. (A and B) BTNL8 (A) and BTNL3 (B) RNA expression (normalized counts) throughout disease time course. BTNL8 expression in whole blood during acute illness (TP1), posttreatment (TP2), and convalescence (TP3) of MIS-C and DV (febrile control) phenotypes compared to healthy controls (HC). Patient carrying BTNL8 p.P456S indicated by red dot. (C–E) BTNL8 (C) and BTNL3 (D) and zonulin (E) protein abundance in plasma of acute MIS-C, KD (Kawasaki Disease), and DV phenotypes compared to healthy controls. Statistical significance determined by Mann–Whitney U test (*P < 0.05; **P < 0.01; ****P < 0.0001).