6MWT	6 min walk test
ACTH	adrenocorticotropic hormone
ADRs	adrenergic receptor antibodies
ADRB2	adrenergic 2-receptor antibody
CHRM3	M3-muscarinic receptor antibody
CHRM4	M4-muscarinic receptor antibody
AT1-R	angiotensin-1 receptor
CO	carbon monoxide
CRH	corticotropin-releasing hormone
CT	computed tomography
DIC	disseminated intravascular coagulation
EBV	Epstein–Barr virus
EQ-5D-5L	European Quality of Life 5 Dimensions 5 Level Version
ETA-R-AAB	Endothelin-1 type A receptor antibody
FcRn	neonatal fragment crystallizable receptor
FSS	Fatigue Severity Scale
GPCRs	G-protein-coupled receptors
HADS	Hospital Anxiety and Depression Scale
IA	immunoadsorption
IgG	immunoglobulin G
IGF-1	Insulin-like growth factor 1
IGF-2	Insulin-like growth factor 2
ISI	Insomnia Severity Index
IVIG	intravenous immunoglobulin
LMM	linear mixed-effects model
ME/CFS	myalgic encephalomyelitis/chronic fatigue syndrome
MLM	multilevel model
MoCA	Montreal Cognitive Assessment
PASC	postacute sequelae of SARS-CoV-2 infection
PCC	long COVID/post-COVID-19 condition
PE	plasmapheresis/plasma exchange
PEM	post-exertional malaise
POTS	postural orthostatic tachycardia syndrome
SARS-CoV-2	severe acute respiratory syndrome coronavirus 2
SNRIs	serotonin–norepinephrine reuptake inhibitors
SSRIs	selective serotonin reuptake inhibitors
alpha1/2-AdR-AAB	adrenergic α1/2-receptor antibody