CXCL2 and mucositis: A transcription quantitative real-time PCR (RT-qPCR) analysis demonstrated that cultured MSCs at passage six expressed very low levels of chemokine receptors, including CXCR2 (Fig. 2a; Supplementary Fig. 2c), which is the receptor of the chemokine that is highly expressed in mucositis, CXCL2.