CCL2 and atrial fibrillation: HMS culture of human AF and NP cells in vitro drives upregulation of the cytokine, inflammatory and neurotrophic molecules TLR2, TLR4, NGF, TNF, GRO, IL-6, IL-8, IL-15, MCP-1, MCP-3, MIG, TGFβ-1 and TNFα.