LPS and Cancer Cell Supernatants Modulate Macrophage Inflammatory Cytokine Responses

Objectives:  Macrophages are cells of the innate immune system that direct the adaptive response to resolve pathogenic challenge. Depending on the factors they encounter in their microenvironment, macrophages polarise to either inflammatory (M1) or suppressive (M2) subsets. In oral pathology, specific disease-associated factors may affect the macrophage polarisation process, perpetuating both inflammatory and immunosuppressive conditions such as periodontitis and oral squamous cell carcinoma (OSCC). This in turn may modulate their responses to subsequent pathogenic stimuli, disrupting their ability to resolve the challenge. Therefore, the present study aimed to investigate the effects of lipopolysaccharide (LPS) from periodontal pathogen P. gingivalis (Pg), and soluble factors produced by OSCC cell line (H357) on the macrophage polarisation process and their subsequent response to LPS challenge.

Methods:  THP-1 (human leukaemia derived monocytic) cells were polarised to M1 or M2 macrophages using PMA + IFNgamma / IL-4 (respectively) in the presence of H357 conditioned media or Pg LPS. Macrophages polarised in media with PMA + IFNgamma / IL-4 served as controls. The macrophages were then stimulated with LPS for 24 hours and supernatants were assayed for the inflammatory cytokines TNFα, IL-1β and IL-6 by ELISA.

Results:  Upon challenge with LPS, macrophages polarised in the presence of LPS showed a reduction in inflammatory cytokine production compared to control macrophages. Conversely, exposure of macrophages to OSCC produced factors during polarisation led to an amplificationof cytokine production in response to LPS.

Conclusion:  The current findings suggest that incubation with LPS during macrophage polarisation may lead to an inflammatory response more reflective of an M2-like population of cells, whereas incubation with OSCC soluble factors may lead to a macrophage inflammatory response more reflective of an M1-like population. The continued study of macrophage/pathogenic stimuli interactions during polarisation may shed light on pathogenic mechanisms in both oral and systemic diseases.