Yang H, et al. - Researchers sought to examine how the interaction between native disc cells and infiltrating macrophages influence inflammation state, matrix homeostasis, and inflammatory cells infiltration. Under healthy culture conditions and in the presence of pro-inflammatory mediators, they stimulated rat nucleus pulposus (NP) cells or annulus fibrosus (AF) cells with conditioned media of RAW 264.7 macrophages and vice versa. Determination of the gene expression of pro-inflammatory mediators, extracellular matrix (ECM)-modifying enzymes, and chemokines, which play important roles in intervertebral disc degeneration (IDD), was done. They noted dramatically up-regulated catabolic cytokines when macrophages were exposed to conditioned media from AF or NP cells with IL-1β stimulation. Similarly, dramatically up-regulated catabolic cytokines were observed when AF or NP cells were exposed to conditioned media from macrophages with IFN-γ stimulation. Outcomes suggest that under degenerated disc inflammatory environment, the biologic interactions between infiltrating macrophages and native disc cells resulted in increasingly severe inflammatory conditions, which may be a self-stimulated process from the macrophages infiltration occurrence.