Introduction

The expression of most TLRs, particularly TLR1 and TLR4, is low on monocytes and even lower on other cell types including granulocytes and immature dendritic cells (iDC). Furthermore, a relatively high degree of variability in TLR surface expression has been reported among normal donors¹. We have evaluated monoclonal antibodies specific for each member of the TLR family to determine the optimal conditions for detection of these antigens by flow cytometry. The following monoclonal antibodies are recommended:

Due to the low density surface expression of the TLR family proteins, it is recommended to use PE labeled monoclonal antibodies for multi-step staining procedures for their optimal detection.

Additionally, TLR surface expression is regulated differentially for each member and in different cell types. Mouse TLR4 is reported to be downregulated on the surface of monocytes upon LPS stimulation^2,3 while reports indicate that human TLR4 is upregulated upon monocyte stimulation⁴. TLR2 is upregulated on blood monocytes by LPS, GM-CSF, IL-1, and IL-10 and downregulated by IL-4, IFN-γ, and TNF-α⁵. Dim expression of TLR2 on purified granulocytes is reported to be even further downregulated by LPS, GM-CSF and TNF-α, while modestly increased by IL-10⁵. Furthermore, human endothelial cells (EC) express predominantly TLR4, but also low levels of TLR2⁶. TLR2 is upregulated on human dermal microvessel endothelial cells and HUVEC when stimulated with LPS, TNF-α, or IFN-γ⁷.

References

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