Objective  To evaluate the antibacterial effect of mononuclear cells (MCs) in the liver lavage solution.

  Methods  For in vitro experiment, MCs were collected from the liver lavage solution of SD rats and divided into the supplement of interleukin (IL)-15 and non-supplement groups. The MCs were co-cultured with Pseudomonas aeruginosa (P. aeruginosa) for 4 h and then the supernatant was collected and MCs were lysed. The bacterial load in the lysate was detected after LB plate culture. The levels of interferon (IFN)-γ and tumor necrosis factor (TNF)-α in the supernatant were measured by enzyme-linked immune absorbent assay (ELISA). For in vivo experiment, 40 SD rats were administered via tracheal injection of P. aeruginosa solution at a dose of 1×10⁹ CFU/mL and randomly divided into four groups (n=10). In the control group, physiological saline was given via gavage. In the immunosuppression group, tacrolimus (FK506) was delivered via gavage. In the MC group, MCs at a dose of 1.0×10⁸ was given via intravenous injection after use of FK506. In the IL-15 pretreated-MC group, IL-15 pretreated-MCs at a dose of 1.0×10⁸ were administered via intravenous injection after application of FK506. The lavage solution of pulmonary alveolus and the rat lung tissue were collected. The bacterial load was detected after LB plate culture. The expression of IFN-γ and TNF-α in the pulmonary alveolus and lung tissue were measured by ELISA and Western blot.

  Results  Compared with MCs alone, IL-15 pretreated-MCs exhibited significantly higher antibacterial capability in vitro. The CFU was 35% of untreated MCs. The synthesis and release capabilities of IFN-γ and TNF-α were significantly enhanced. Compared with the control group, the quantity of immune cells in the lung tissue was decreased and the bacterial load in the lung tissue and the lavage solution of pulmonary alveolus was significantly increased, whereas the expression levels of IFN-γ and TNF-α tended to decline in the immunosuppression group. Administration of IL-15 pretreated-MCs significantly enhanced the quantity of immune cells in the lung tissue, decreased the bacterial load and increased the secretion of IFN-γ and TNF-α.

  Conclusions  MCs in the liver lavage solution exhibit favorable antibacterial activity. Under immunosuppression condition, the defense capability of the host against the opportunistic pathogenic bacteria is significantly enhanced.