Parvimonas micra-polarized M2-like tumor-associated macrophages accelerate colorectal cancer development via IL-8 secretion

Parvimonas micra (Pm), a periodontal pathogen, has been implicated in the impairment of anti-tumor responses in colorectal cancer (CRC). The tumor microenvironment in CRC involves tumor-associated macrophages (TAMs), which are pivotal in modulating tumor-associated immune responses. The polarization of TAMs towards an M2-like phenotype promotes CRC progression by suppressing the immune system. However, the mechanisms by which Pm affects the progression of CRC remain inadequately elucidated. In this study, we explored the impact of Pm infection on CRC cell characteristics, including proliferation, chemoresistance, migration, and macrophage polarization. We found that Pm-infected THP-1-derived macrophages exhibited elevated interleukin-10 levels, a well-established M2 marker. Conditioned media from Pm-treated THP-1 cells significantly enhanced CRC cell proliferation, cisplatin resistance, and migration, and interleukin-8 was identified as a key factor. Consistent with the in vitro results, an azoxymethane/dextran sodium sulfate mouse model treated with oral Pm showed accelerated CRC tumor growth. These results offer mechanistic insights into the influence of Pm infection on tumor microenvironment in CRC through M2-like macrophage polarization. The identified pathways may serve as potential targets for therapeutic interventions for CRC.