Interaction of Biofilms With Human Peripheral Blood Mononuclear Cells.

The human immune cell response against bacterial biofilms is a crucial, but still poorly investigated area of research. Herein, we aim to establish an host cell-biofilm interaction model suitable to investigate the peripheral blood mononuclear cell (PBMC) response to biofilms. . biofilms were obtained by incubating bacteria in complete RPMI 1640 medium with 10% human plasma for 24 h. PBMC obtained from healthy donors were added to preformed . biofilms. Following a further 24 h incubation, we assessed (i) PBMC viability and activation; (ii) cytokine profiles in the supernatants; and (iii) CFU counts of biofilm forming bacteria. Cell-death was <10% upon 24 h incubation of PBMC with . biofilms. PBMC incubated for 24 h with preformed . biofilms were significantly more activated compared to PBMC incubated alone. Interestingly, a marked activation of CD56CD3 natural killer (NK) cells was observed that reached 60% of NK cells as an average of different donors. In the culture supernatants of PBMC co-cultured with . biofilms, not only pro-inflammatory (IL-1β, IFN-γ, IL-6, and TNF-α) but also anti-inflammatory (IL-10) cytokines were significantly increased as compared to PBMC incubated alone. Furthermore, incubation of biofilms with PBMC, caused a statistically significant increase in the CFU number of , as compared to biofilms incubated without PBMC. In order to assess whether PBMC products could stimulate the growth of . biofilms, we incubated preformed biofilms with or without supernatants obtained from the co-cultures of PBMC with biofilms. In the presence of the supernatants, the CFU count of biofilm-derived . , was two to seven times higher than those of biofilms incubated without supernatants ( < 0.01). Overall, the results obtained shed light on the reciprocal interaction between human PBMC and . biofilms. . biofilms induced PBMC activation and cytokine secretion but, in turn, the presence of PBMC and/or PBMC-derived components enhanced the number of . biofilm associated bacteria. This may indicate a successful bacterial defensive/persistence strategy against immune response.