ACE-2	Angiotensin-converting enzyme 2
ADAM17	A disintegrin and metalloprotease 17
ATR1	Angiotensin II receptor type 1
ATR2	Angiotensin II receptor type 2
ACE D	Angiotensin-converting enzyme deletion
ACE I	Angiotensin-converting enzyme insertion
APC	Antigen presenting cells
ADHD	Attention deficit hyperactivity disorder
BBB	Blood–brain barrier
CDC	Centers for Disease Control and Prevention
CCL2	Chemokine C-C motif chemokine ligand 2
CCL3	Chemokine C-C motif chemokine ligand 3
CCL5	Chemokine C-C motif chemokine ligand 5
CX3CL1	Chemokine fractalkine
CCR5	C-C chemokine receptor type 5
CYP	Children and young people
COVID-19	Coronavirus disease 2019
CCS	Chronic COVID-19 syndrome
CX3CR1	CX3C motif chemokine receptor 1
CS	Cytokine storm
DAMP	Damage-associated molecular pattern
DVG	Defective viral genome
DNA	Deoxyribonucleic acid
EDs	Emergency departments
EV	Extracellular vesicle
F. prausnitzii	Faecalibacterium prausnitzii
Fc	Fragment crystallizable
GI	Gastrointestinal
AWMF	German Association of Scientific Medical Societies
IS	Immune system
IgA	Immunoglobulin A
IgG	Immunoglobulin G
IgM	Immunoglobulin M
ICAM-1	Intercellular adhesion molecule 1
IFN	Interferon
IP-10	Interferon gamma-inducible protein-10
IFN-γ	Interferon-gamma
IL-1, IL-6, IL-8, IL-15	Interleukin 1, 6, 8, 15
IL-1α	Interleukin 1α
IL-1β	Interleukin 1β
IHR	International Health Regulations
IEL	Intraepithelial CD8+ lymphocytes
JDM	Juvenile dermatomyositis
KD	Kawasaki disease
KKS	Kinin–kallikrein system
LC	Long COVID
MRI	Magnetic resonance imaging
MMP	Matrix metalloproteinase
MMP7	Matrix metalloproteinase 7
MMP9	Matrix metalloproteinase 9
MERS	Middle East respiratory syndrome
mRNA	Messenger RNA
MGB	Microbiota-gut-brain
miRNAs	MicroRNAs
MERS	Middle East respiratory syndrome
MCP-1	Monocyte chemoattractant protein-1
MIS-C	Multisystem inflammatory syndrome in children
MIS-N	Multisystem inflammatory syndrome in neonates
MYD88	Myeloid differentiation primary response 88
NHS	National Health Service
NICE	National Institute for Health and Care Excellence
NIHR	National Institute for Health Research
NIH	National Institutes of Health
NF-κB	Nuclear factor kappa-light-chain-enhancer of activated B cells
PAMP	Pathogen-associated molecular pattern
PANS	Pediatric acute-onset neuropsychiatric syndrome
PIMS-TS	Pediatric Multisystem Inflammatory Syndrome, Temporarily Associated with SARS-CoV-2
PLVAP	Plasmalemma vesicle-associated protein
PCR	Polymerase chain reaction
PC	Post COVID syndrome
PCC	Post COVID-19 condition
PASC	Post-acute sequelae of SARS-CoV-2 infection
ROS	Reactive oxygen species
RBD	Receptor binding domain
RSPO3	Regulator of angiogenesis r-spondin-3
Tregs	Regulatory T lymphocytes
RAS	Renin–angiotensin system
RT-PCR	Reverse transcriptase polymerase chain reaction
RNA	Ribonucleic acid
SARS	Severe acute respiratory syndrome
SARS-CoV-2	Severe acute respiratory syndrome coronavirus 2
S	Spike protein
Th1	T-helper 1 or T helper type 1
Th2	T-helper 2 or T helper type 2
Th17	T-helper 17 or T helper type 17
TJs	Tight junctions
TLR2	Toll-like receptor 2
TLR4	Toll-like receptor 4
TLR	Toll-like receptors
TMPRSS2	Transmembrane serine protease 2
TMPRSS4	Transmembrane serine protease 4
TNF-α	Tumor necrosis factor alpha
TACE	Tumor necrosis factor-alpha converting enzyme
US	United States
FDA	U.S. Food and Drug Administration
UK	United Kingdom
UKRI	UK Research and Innovation
VCAM-1	Vascular cell adhesion molecule 1
WHO	World Health Organization
Increased	↑
Decreased	↓
Present	+
Absent/Missing	-