Modulation of allograft immune responses by Porphyromonas gingivalis lipopolysaccharide administration in a rat model of kidney transplantation

Abstract

Periodontitis is a chronic inflammatory disease that affects the periodontal tissues. Although it is associated with various systemic diseases, the impact of periodontitis on kidney transplantation (KT) outcomes, particularly allograft rejection, remains unclear. This study investigated the effect of periodontitis on transplant immunity, specifically examining Porphyromonas gingivalis-derived lipopolysaccharide (LPS-PG). In vitro experiments revealed that LPS-PG increased regulatory T cells (Tregs) in Lewis rat spleen cells. In a mixed lymphocyte reaction assay, concentrations of interferon-γ, indicative of alloreactivity, were lower than in controls when LPS-PG was added to the culture and when LPS-PG-administered Lewis rat spleen cells were used as responders. In a rat KT model, LPS-PG administration to recipients promoted mild tubulitis and low serum creatinine and blood urea nitrogen levels 5 days post-KT compared with PBS-administered controls. Furthermore, LPS-PG-administered recipients had an elevated Treg proportion in their peripheral blood and spleen cells, and increased infiltrating Tregs in kidney allografts, compared with controls. The elevated Treg proportion in peripheral blood and spleen cells had a significant negative correlation with serum creatinine, suggesting elevated Tregs modulated allograft rejection. These findings suggest that periodontitis might modulate alloimmune reactivity through LPS-PG and Tregs, offering insights to refine immunosuppressive strategies for KT recipients.

Keywords: Porphyromonas gingivalis; Endotoxin tolerance; Kidney transplantation; Lipopolysaccharide; Periodontitis.

Figure 1

(a) Flow cytometry analysis of in vitro cultured LEW spleen cells with or without LPS-PG. The proportion of Tregs in total CD4 + T cells was determined. (b) IFN-γ concentrations after MLR assay with graded concentrations of LPS-PG were analyzed by ELISA. Statistical analysis was conducted to identify differences between groups. *p < 0.05, **p < 0.005, *p < 0.001.

Figure 2

(a) Study design for the in vivo experiment. (b) IFN-γ concentrations after MLR assay using spleen cells from both groups as responder cells. (c) The association between IFN-γ concentration after MLR assay and Treg proportion before the MLR assay, determined by flow cytometry. Statistical analysis was conducted to identify differences between groups. *p < 0.05.

Figure 3

(a) Study design for the kidney transplantation experiment. (b) Serum creatinine and (c) blood urea nitrogen concentrations 5 days after transplantation. (d) Histology and immunohistochemistry of kidney allografts 5 days after transplantation. Yellow arrows indicate mononuclear cells infiltrating the tubule and red arrows indicate Foxp3 + cells. Scale bar = 50 μm. (e) The tubulitis score of each group was calculated as described in the Methods. (f) Calculated number of Foxp3 + cells in a high-power field using a digital image analysis program. Statistical analysis was conducted to identify differences between groups. *p < 0.05, **p < 0.005.

Figure 4

(a) Flow cytometry analysis of spleen cells and peripheral blood from both groups 5 days after transplantation. The proportion of Tregs in total CD4 + T cells was determined. (b) IL-10 concentrations in the serum 5 days after transplantation measured by ELISA. (c) The association of creatinine with spleen cells and (d) peripheral blood. Statistical analysis was conducted to identify differences between groups. *p < 0.05, **p < 0.005.