Association of Trichomonas vaginalis with its symbiont Mycoplasma hominis synergistically upregulates the in vitro proinflammatory response of human monocytes

Objectives Trichomonas vaginalis is the causative agent of trichomoniasis, one of the most common sexually transmitted diseases worldwide. In recent years we have described the symbiotic relationship between T vaginalis and Mycoplasma hominis. How this biological association might affect the pathogenicity of one or both the microorganisms is still unknown. Since local inflammation is thought to play a central role in T vaginalis infection, we investigated the in vitro response of human macrophages to naturally mycoplasma-free T vaginalis, as compared to a mycoplasma-infected trichomonad isolate. Methods THP-1 cells were stimulated with two isogenic T vaginalis isolates, one naturally mycoplasma-free and one stably associated with M hominis, and secreted cytokines measured by ELISA. Nuclear factor κB (NFκB) involvement in THP-1 response to T vaginalis and M hominis was evaluated by means of a reporter system based on detection of alkaline phosphatase activity. Results We found that the presence of M hominis upregulates the expression of a panel of proinflammatory cytokines in a synergistic fashion. We also found that the upregulation of the proinflammatory response by THP-1 cells involves the transcription factor NFκB. Conclusions These findings suggest that the presence of M hominis in T vaginalis isolates might play a key role in inflammation during trichomoniasis, thus affecting the severity of the disease. The synergistic upregulation of the macrophage proinflammatory response might also affect some important clinical conditions associated with T vaginalis infection, such as the increased risk of acquiring cervical cancer or HIV, which are thought to be affected by the inflammatory milieu during trichomoniasis.