Clinical severity and local inflammatory responses in animal models of sepsis

Introduction

Severe sepsis carries high morbidity and mortality. Pre clinical research predominantly utilises animal models although their reproducibility may vary, thus impairing understanding of disease. We sought to determine the reproducibility of two murine models by assessing clinical severity and local immune cell response 24 hours after septic insult.

Methods

Intraperitoneal faecal slurry (FS) or zymosan was given to induce acute peritonitis in 11 and 12 male C57/Bl mice (8 to 12 weeks, 18 to 32 g). A control group received saline only (n = 5). In surviving animals at 24 hours, clinical severity was scored as severe, moderate or mild according to appearance and alertness. Peritoneal lavage was performed to obtain immune cells. Analysis by antibody labelling (F4/80, GR-1, CD3 and CD19) for fluorescence-assisted cell sorting identified numbers of macrophages, neutrophils, T and B cells. Logistic regression (odds ratio, OR) was used to determine the relationship of cell numbers with severity (reported if P < 0.05).

Results

Clinical severity varied markedly despite similar dosing (see Table 1). At 24 hours, total intraperitoneal immune cells increased in both models and with clinical severity (OR 0.83). Neutrophils predominated after septic insult and also rose with severity (OR 0.75). Compared with control, macrophage populations did not change in either model while B and T lymphocytes fell. A cell population that expressed both F4/80 and GR-1 - that is, markers for macrophages and neutrophils, respectively - occurred only in the FS model.

Table 1 Number of animals according to clinical severity (with inclusive mortality)

Conclusions

Individual variability occurs in both faecal and zymosan peritonitis models as shown by heterogeneous clinical responses and local immune cell numbers to the same dose in similar animals. The cellular immune response in both models is consistent with current understanding of infection-induced inflammation. Neutrophils, but not macrophages, rose in proportion to worsening clinical severity. The significance of F4/80⁺/GR-1⁺ cells in the FS model requires further evaluation.