Contribution of the gut association lymphoid tissue inflammatory response under bacterial translocation and sepsis challenge is the relevant factor for the onset of multiple organ dysfunction syndrome

Background

The gastrointestinal tract has been implicated in sepsis and organ failure by bacterial translocation (BT) and gut-immune system crosstalk with the systemic immunity, but is not yet clearly demonstrated in clinics. Herein we examined the role of gut-associated lymphoid tissue on host inflammatory response by BT as a contributing feature for multiorgan dysfunction in sepsis.

Methods

Wistar rats were challenged to BT (10 ml Escherichia coli R6, 10¹⁰ colony-forming units (CFU)/ml), sepsis (2 ml Enterobacter cloacae 89, 10⁷ CFU/ml), and sepsis plus BT, with/without mesenteric lymph flow interruption (MLFI) by canulation and lymph deviation or by mesenteric lymphadenectomy plus lymph duct ligation 5 days before in the following groups (n = 20/group): BT (BT-G); BT with MLFI (BTL-G); sepsis (S-G); sepsis with MLFI (SL-G); combination of BT to sepsis (C-G); combination with MLFI (CL-G); sham-BT (SBT-G); sham-sepsis (SS-G); and sham-combination (SC-G). Samples (mesenteric lymph node, blood, spleen and liver) were collected 2 hours after and were cultured for bacterial recovery of both sepsis and BT origin. Tissue perfusion (jejunum, ileum, liver, kidneys) and mesenteric microcirculation were monitored at 0 and 2 hours. Systemic blood and intestinal lymph were collected for cell count and phenotyping. The groups' mortality was followed.

Results

The BT index was not modified by MLFI, but BT alone and sepsis plus BT provoked significant hypoperfusion in all organs plus microcirculation injuries. The MLFI at BTL-G and CL-G completely abrogated tissue hypoperfusion (Figure 1) and microcirculation injury. The lymph-cell count post BT, sepsis and combined challenges was significantly increased compared with controls although the composition was similar (98% to 99% lymphocytes and 1% to 2% others). The blood-leucocyte count was unchanged in all groups (Figure 2). TCD3⁺ over B lymphocytes (CD45RA⁺) predominated in both lymph (83%/7%) and blood (68%/3%) (P < 0.05), and their percentages did not differ between groups. The CD4⁺/CD8⁺ ratio also did not differ between groups. Naïve cells (CD4⁺CD45RC⁺) predominated in the TCD4⁺ population in lymph, and memory cells (CD4⁺CD45RC^-) in blood. CD8⁺CD45RC⁺ cells predominated in both lymph and blood. The proportion of T-regulatory (CD4⁺CD8⁺/CD25⁺) cells was low in both lymph and blood for all groups (Figures 3 and 4). MLFI completely prevented the death observed in C-G (LD₅₀).

Figure 1

Comparison of the tissue perfusion (jejunum, ileum, liver and kidneys) in Δ% and the mortality index (DL) in all groups. *P < 0.05.

Figure 2

Total number of leukocytes in the mesenteric lymph and blood per mm³ of all groups. *P < 0.05.

Figure 3

CD4-positive T-cell subsets (N, naïve; M, memory; and Reg, regulatory) in the mesenteric lymph and blood of all groups by flow cytometry.

Figure 4

CD8-positive T-cell subsets (N, naïve; M, memory; and Reg, regulatory) in the mesenteric lymph and blood of all groups by flow cytometry.

Conclusion

The gut-associated lymphoid tissue response following bacterial challenge and its crosstalk with the systemic immunity via the lymphatic system is the key factor related to the aggravation of systemic inflammation and death in sepsis.