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Letter to editor: Evaluation of the relationship between TREM‐1/TREM‐2 ratio and clinical course in COVID‐19 pneumonia

Dear editor, we read with great interest the wellwritten article by Dr Kerget et al with the main objective of investigating the role of the TREM1/TREM2 ratio on patients with COVID19 pneumonia.1 The article pointed that TREM1 and TREM2 have an important role in inflammation and TREM1/TREM2 ratio was higher in severe COVID19 patients compared with the moderate COVID19 patients. We have certain comments to understand the conclusions of this article. To begin with, the measurement of biochemical markers, the triggering receptor expressed on myeloid cells1 (TREM1) is mainly expressed on neutrophils and monocytes in a cell membranebound form. A soluble form of TREM1(sTREM1), which lacks the cytoplasmic tail and transmembrane part, was detected in the blood in recent studies. Since the authors mentioned “serum TREM1,” we were confused whether they detected TREM1 or sTREM1. Regarding the demographic features, we wanted to know more about the treatment and the kidney functions of the patients. As we all know, treatment could affect the serum levels of sTREM1 or other inflammatory cytokines. Besides, it has been reported that TREM1 seems to be correlated with renal function and acute kidney injury following COVID19 infection has been described in recent literature. Lastly, according to a previous report,2 lesions could be assessed in four lung zones and the extent of ILD lesions was semiquantitatively scored based on the percentage of the lung parenchyma involved in each zone. The COVID19 pandemic is characterised by interstitial pneumonia. We are curious to see if the high TREM1/TREM2 ratio could predict the distribution of ILD. Furthermore, we wanted to know if the TREM1/TREM2 ratio in urine might be correlated with clinical course in COVID19 pneumonia since urine was obtained in this article. We would be glad to hear the opinion of the author on the points, to get a more convincing conclusion.