Purpose: Intervertebral disc with Propionibacterium acnes (P. acnes) is suggested to be an etiology of Modic type I changes in the adjacent bone marrow. However it is unknown if disc cells can respond to P. acnes and if bone marrow cells respond to bacterial and disc metabolites draining from infected discs.
Methods: Human disc cells (n = 10) were co-cultured with 10- and 100-fold excess of P. acnes over disc cells for 3 h and 24 h. Lipopolysaccharide was used as positive control. Expression of IL1, IL6, IL8, and CCL2 by disc cells was quantified by quantitative PCR. Lipase activity was measured in culture supernatants (n = 6). Human vertebral bone marrow mononuclear cells (BMNCs) (n = 2) were cultured in conditioned media from disc cell/P. acnes co-cultures and expression of IL1, IL6, IL8, and CCL2 was measured after 24 h.
Results: All disc cells responded to lipopolysaccharide but only 6/10 responded to P. acnes with increased cytokine expression. Cytokine increase was time- but not P. acnes concentration-dependent. Disc cell responsiveness was associated with the presence of lumbar Modic changes in the donor. Lipase activity was increased independent of disc cell responsiveness. BMNCs responded with inflammatory activity only when cultured in supernatants from responsive disc cell lines.
Conclusion: Disc cell responsiveness to P. acnes associates with the presence of lumbar Modic changes. Furthermore, bone marrow cells had an inflammatory response to the cocktail of disc cytokines and P. acnes metabolites. These data indicate that low virulent P. acnes infection of the disc is a potential exacerbating factor to Modic changes.
Keywords: Bone marrow; Co-culture; Immune response; Inflammation; Modic change; P. acnes.