MCAM and atrial fibrillation: Trafficking fibrocytes express chemokine receptors CCR5,43 CCR722 and CXCR4.22,44 Studies have reported increased CCR5 expression in AF and NP cells45 and chemokines CCL2/7 in dNP.46 Bone marrow cells, such as CD146+ MSCs,47 may have a potential to migrate into the NP, possibly by control of SDF1.48 CCL5 could interact with CCR1/3/5 in NPC and was up-regulated under inflammatory stimuli.49 CXCR4 is a receptor of SDF150 and CXCL12,44 which was found upregulated in degenerated discs and implicated in disc angiogenesis50 and cellular apoptosis51 via PI3K/NF-κB pathway.