TABLE 1.
Cell- and stimulus-specific expression patterns of human TLRsa
| Receptor | Cell type (reference) | Regulation |
|---|---|---|
| TLR1 | Ubiquitous (63) | No significant regulation except for downregulation in T cells after exposure to PHA (53) |
| TLR2 | Restricted expression, undetectable in lymphoid cells, expressed in PMLs, DCs, and monocytes (53) | Induced by LPS (53, 85) |
| TLR3 | Expressed on DC and NK cells (24, 53) | Absent in precursor monocytes, induced by differentiation, decreased upon maturation (53) |
| TLR4 | Expressed in a variety of cell types, such as macrophages, DCs, ECs, not in lymphocytes (48, 53) | Expression enhanced by proinflammatory cytokines and bacterial products, downregulated by anti-inflammatory cytokines (53) |
| TLR5 | Expressed in monocytes, immature DCs, epithelial, NK, and T cells (14, 24, 56) | No significant modulation by cytokines or LPS (24, 53) |
| TLR6 | High expression in B cells, lower in monocytes and NK cells (24) | Not induced by proinflammatory cytokines or LPS (24) |
| TLR7 | B cells, plasmacytoid precursor DC (24, 32) | Highly induced by IL-6, moderately by other cytokines (86) |
| TLR8 | Monocytes, low in NK and T cells (24, 32) | Highly induced by gamma interferon and LPS, moderately by other cytokines (85) |
| TLR9 | Plasmacytoid precursor DCs, B-cells, macrophages, PMLs, NK cells, and microglial cells (3, 32) | Induced by gamma interferon and LPS (3, 36) |
| TLR10 | B cells, low in plasmacytoid precursor DCs (24) | No significant modulation by cytokines or LPS (86) |
a
Abbreviations: DC, dendritic cell; EC, endothelial cell; PML, polymorphonuclear leukocytes; NK, natural killer cell; PHA, phytohemagglutinin. References are indicated.