Expression of CD68 in non-myeloid cell types

Area of Science:

• Immunology
• Cell Biology

Background:

• CD68 is widely used as a selective marker for human monocytes and macrophages.
• Its expression is believed to be controlled by a macrophage-specific promoter.
• However, immunohistochemical studies suggest CD68 antibodies react with other cell types.

Purpose of the Study:

• To investigate the expression of CD68 in various primary cells and carcinoma cell lines.
• To determine if CD68 is a selective macrophage marker.

Main Methods:

• Immunohistochemistry
• Flow cytometry
• Western blot analysis
• Quantitative reverse transcription PCR (qRT-PCR)
• Cloning of 5'-sequences and determination of transcription start sites

Main Results:

• CD68 immunoreactivity was detected in lymphocytes, tumor cell lines, fibroblasts, and endothelial cells, in addition to macrophages and monocytes.
• Staining intensity varied depending on the cell type, antibody clone, and fixation technique.
• mRNA expression of CD68 was found in macrophages, monocytes, fibroblasts, endothelial cells, and tumor cells.
• Macrophages and fibroblasts initiate transcription from different start sites within the promoter region, indicating alternative promoter architecture.

Conclusions:

• CD68 is not a selective marker for macrophages.
• CD68 is a lysosomal protein that is enriched in macrophages but also expressed in other cell types.
• Caution is advised when using CD68 as a marker, especially with the KP1 antibody clone and in frozen or formalin-fixed paraffin-embedded tissues.