Table 1.
TLRs expressed in microglia (human (H) and mouse (M)) and ligands/agonists classified in PAMPs and DAMPs.
| TLR | Expression Level | PAMPs | DAMPs | |
|---|---|---|---|---|
| M | H | |||
| 1 | + | +++ | Lipoproteins [67] | α-syn [68] |
| 2 | +++++ | ++++ | PG [67,69], lipoproteins, LTA, zymosan [67], synthetic bacterial lipopeptide Pam3CysSK4 [70] | α-syn [68,71], Aβ [72], gangliosides, hyaluronic acid [73] |
| 3 | + | ++ | Poly(I:C), viral dsRNA [67,74] | mRNA from apoptotic cells [75], stathmin[76] |
| 4 | + | ++ | LPS [77], monophosphoryl lipid A [78] | Aβ [79], α-syn [80,81], MPP+ [82], HSP60, fibrinogen [73] |
| 5 | + | + | Bacterial flagellin [67] | ND |
| 6 | + | PG [69], lipoproteins, LTA [67] | HMGB1 [83] | |
| 7 | ++++ | ++ | Loxoribine [84], miR [85], ssRNA [67,86] | Self RNA, microRNA [83] |
| 8 | + | + | ssRNA [67] | Self RNA, microRNA [83] |
| 9 | ++++ | + | CpG-DNA [87,88], CpG-ODN [84,89], bacterial DNA [67] | DNA degenerating neurons [90], HMGB1 [91] |
| 10 | NF | + | ND | ND |
| 11 | + | NF | Profilin [92] | ND |
| 12 | + | NF | ND | ND |
| 13 | ++ | NF | Bacterial RNA [93] | ND |
Abbreviations: CpG-DNA, cytosine-guanosine dinucleotides; CpG-ODN, cytosine-guanosine oligodeoxynucleotide; dsRNA, double-stranded RNA; HSP60, heat shock protein 60; LTA, lipoteichoic acid; MPP+, 1-methyl-4-phenylpyridinium; NF, not found; PG, peptidoglycan; Poly(I:C), polyinosinic-polycytidylic acid; ssRNA, single-stranded RNA. Legends: + (0.1-10.0 (fragments per kilobase of transcript per million mapped reads) FPKM), ++ (10.1-30.0 FPKM), +++ (30.1-60.0 FPKM), ++++ (60.1-90.0 FPKM), +++++ (>90.0 FPKM). Data source: https://www.brainrnaseq.org/. RNAseq data for mouse and human microglia obtained from [94,95], respectively.