IFIT3 and atrial fibrillation: In non-degenerative discs (Grade I), single cells that were positive for IGFBP3 were sporadically detected in the AF, although young AF tissue was mostly negative for IGFBP3 (Fig. 7c); IFIT3 positive cells were also observed in the AF of normal grade I discs (Fig. 7f), although immunostaining was weaker in non-degenerative compared to degenerative discs.