Table 3.
Summary of studies quantifying the increased activation or protein expression of TLR and NLR for innate immune system cells following bacterial infections associated with severe COVID-19, ALI/ARDS and/or sepsis. Blank squares indicate that no data were found regarding the activity or expression pattern of the receptor. GRAM POS = Gram-positive bacterium, GRAM AMBI = bacterium that yields ambiguous Gram staining, GRAM NEG = Gram-negative bacterium and NO GRAM means that Gram staining is irrelevant. – indicates no change, ^ indicates increased activation or protein expression, V indicates downregulation or decreased protein expression, +/- indicates conflicting reports about whether there is increased activity or protein expression, -/V indicates conflicting reports about whether there is no change or downregulation and a blank square indicates no available information. PGN = peptidoglycan; LTA = lymphotoxin alpha; HSP = heat shock protein; HMGB1 = High Mobility Group Box 1 protein; dsRNA = double-stranded ribonucleic acid; polyI:C = polymer composed of inosine and cytosine; DAMP = damage-associated proteins; Gram+ = expressed by Gram-positive bacteria; lipopeps = lipopolypeptides; ssRNA = single-stranded ribonucleic acids; CpG DNA = deoxyribonucleic acid high in cytosine and guanine, typifying a microbial genomic origin; mtDNA = deoxyribonucleic acid derived from mitochondria; DAP = diaminopimelic acid, a bacterial cell wall component; MDP = muramyl dipeptide, a bacterial cell wall component and ? = activators not presently known.
| TLR 1 |
TLR 2 |
TLR 3 |
TLR 4 |
TLR 5 |
TLR 6 |
TLR 7 |
TLR 8 |
TLR 9 |
TLR 10 |
NOD 1 |
NOD 2 |
NL-RP3 | RIG 1 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Lipopeptides | Gram- PGN, LTA & HSP, HMGB1 |
ds-RNA, polyI:C, DAMP |
Gram+ LPS & HSP, HMGB1 |
Flagellin | LTA, lipopeps | ss-RNA | ss- RNA & pyogenic Bacteria |
CpG DNA & mtDNA |
Retroviral RNA | Meso-DAP | MDP | ? | Viral RNA | |
| GRAM POS | ||||||||||||||
| Group A Streptococci | ^ | ^ | - | ^ | - | - | - | ^ | - | - | ^ | ^ | ||
| Group B Streptococci | - | ^ | ^ | ^ | - | - | ^ | |||||||
| Staphylococcus aureus | ^ | ^ | ^ | ^ | - | ^ | ^ | |||||||
| GRAM AMBI | ||||||||||||||
| Mycobacterium tuberculosis | ^ | ^ | +/- | ^ | ^ | ^ | ^ | |||||||
| GRAM NEG | ||||||||||||||
| Klebsiella pneumoniae | ^ | ^ | ^ | ^ | ^ | |||||||||
| Haemophilus influenzae | ^ | +/- | - | ^ | ^ | ^ | ||||||||
| Legionella pneumophila | ^ | ^ | ^ | - | - | ^ | ||||||||
| Chlamydia pneumoniae | ^ | ^ | ^ | ^ | ^ | |||||||||
| Neisseria meningitidis | ^ | ^ | ^ | ^ | ^ | ^ | ||||||||
| Pseudomonas aeruginosa | ^ | ^ | ^ | ^ | ^ | ^ | ||||||||
| NO GRAM | ||||||||||||||
| Mycoplasma pneumoniae | ^ | ^ | ^ | ^ | - | - | ^ | |||||||
| BACTERIA CONCENSUS | ^ | ^ | ^ | ^ | +/- | ^ | ^ |