S100A7 and atrial fibrillation: Many of the substances that constitute the innate immune system have been identified in AF and have been shown to have significant antimicrobial properties, including α-defensins (human neutrophil defensins 1–3), calprotectin, secretory leukocyte protease inhibitor, psoriasin (S100A7), lactoferrin, lysozyme, bactericidal/ permeability-increasing protein, and cathelicidin (15).