IGHG3 and COVID-19: IA-SRM analysis of negative or positive convalescent COVID-19 plasma confirmed the true positive immune response with IgG1/IgG3/IgA1 pairing and provided a 385 ng/mL cut-off for anti-RBD IgG1 to detect COVID-19 convalescent plasma with nearly 100% sensitivity and specificity [10].