Abstract
The article “CD204-Expressing Tumor-Associated Macrophages Are Associated With Malignant, High-Grade, and Hormone Receptor–Negative Canine Mammary Gland Tumors” does not provide evidence that CD204 is a marker for M2 macrophages.
Keywords
In the article “CD204-Expressing Tumor-Associated Macrophages Are Associated With Malignant, High-Grade, and Hormone Receptor–Negative Canine Mammary Gland Tumors,” 3 the authors studied the expression of CD204 in canine mammary tumors, inferring that the antigen expression allowed the detection of polarized M2 macrophages. Unfortunately, no references are provided to confirm that this marker can detect M2 macrophages in dogs.
CD204 is a scavenger receptor and its expression is well described in the article “The Class A macrophage scavenger receptor CD204 is a useful immunohistochemical marker of canine histiocytic sarcoma.” 2 The authors found positive labeling of resident macrophages in several control organs (eg, alveolar macrophages, Kupffer cells, red pulp macrophages of the spleen, dermal macrophages, macrophages within the lymph node sinuses) and they concluded CD204 was a marker for macrophages, without specifying the polarization. Moreover in the same article they tested 50 histiocytic sarcomas. All were positive for CD204, while CD163 positivity was found in 54% of the tumor. CD163 is considered a marker for M2 polarization in humans. Nevertheless, the authors of “Morphologic, Phenotypic, and Transcriptomic Characterization of Classically and Alternatively Activated Canine Blood-Derived Macrophages in Vitro” 1 provided evidence that CD163 is not discriminant for macrophage polarization in dogs. From their studies, CD206 appeared to be a more appropriate marker.
In conclusion, I would like the authors of the article “CD204-Expressing Tumor-Associated Macrophages Are Associated With Malignant, High-Grade, and Hormone Receptor–Negative Canine Mammary Gland Tumors” to provide evidence that CD204 is a marker for M2 polarization in dog tissues or that they consequently change their article.