Effect of hypothermia on splenic leukocyte modulation and survival duration in severely septic rats

Abstract

Background Therapeutic hypothermia in severe septic shock is associated with prolonged survival. We hypothesized that moderate hypothermia would prolong survival and modulate the inflammatory response in rats with septic shock by exerting its therapeutic effect on splenic leukocytes. Materials and Methods Severe septic shock was created in rats by cecal ligation and incision (CLI). One hour after CLI or laparotomy, rats were randomized to sham, normothermia (NT), or 4 hours of hypothermia (HT) followed by 2 hours of rewarming. Hypothermia (3l±1°C) was induced using a cooling blanket, and monitored via a rectal temperature probe. Results Survival duration was 2.78±1.0 hours in NT rats and 8.33±0.32 hours in HT rats (n=8/group, p<0.0001). In separate groups, three hours after CLI, the spleen weight was significantly smaller in NT rats (769±100 mg) than in HT rats (947±157 mg, p=0.04). Fluorescent immunostaining of formyl peptide receptors (FPR) on leukocytes in spleen tissue showed considerably higher FPR expression in HT rats than in NT rats. Significantly elevated pro-inflammatory cytokines and myeloperoxidase (MPO) enzyme in plasma were found in NT rats compared with HT rats. Anti-inflammatory cytokine, IL-10, was significantly higher in HT rats. Both pro-inflammatory cytokines and plasma MPO were significantly reduced in splenectomized NT rats. Conclusions Moderate hypothermic therapy significantly prolongs the survival duration of rats with severe septic shock. Hypothermia dampens the inflammatory response during septic shock by modulating the spleen to an anti-inflammatory mode and preventing the spleen from releasing activated splenic leukocytes into the blood.

Pulsed Ultrasound of the Spleen Prolongs Survival of Rats With Severe Intra-abdominal Sepsis

“…35 We found that pUS of the spleen abrogated proinflammatory cytokine production and the exodus of splenic leukocytes into circulation in the early phases after CLI. Consistent with prior studies, 14 CLI induced significant contraction in splenic weight of the control animals, suggesting a migration of reservoir splenic leukocytes into the circulation, an effect that was not mitigated by abdominal washout. However, after pUS treatment, splenic contraction while still present was appreciably attenuated, and corresponding peripheral leukocyte counts were reduced to a level similar to septic animals that had undergone splenectomy (Fig.…”

“…Thus, as anticipated, this only delayed the development of fatal multiorgan failure due to intraabdominal sepsis and did not prevent mortality within 24 h. Simultaneous splenectomy performed at the time of surgical washout further prolonged the survival of the rats after CLI, supporting the theory that the spleen is a significant contributor to the acute inflammatory responses that account for much of the morbidity and mortality associated with septic shock. 14 In its immunoregulatory role, the spleen is the primary source of TNF-a production and acts as a reservoir for most of the body's phagocytic cells. 20 There are limited published studies on the role of the spleen in sepsis, and human clinical data that compare the outcomes of asplenic to normal patients in sepsis are not present in the literature.…”

“…24,25 In addition, we and others have shown that splenectomy reduces acute inflammatory responses, attenuates the cytokine storm that occurs during sepsis, and protects against mortality in in vivo models of sepsis. [12][13][14] In a similar cecal ligation and puncture (CLP) model as used in this study, splenectomy significantly reduces the acute elevation in myeloperoxidase (MPO) and cytokines IL-1b, IL-6, IL-10, IL-17, TNF-a, and IFN-g, and MCP-1, the dysregulated immunological profile that leads to end-organ damage in sepsis 14 However, its feasibility as a therapeutic intervention is limited by its invasive nature and the undesired effects, in addition to increased susceptibility to encapsulated bacterial infection, that may occur after the acute phase immunologic response to sepsis. Here we demonstrated that pulsed low-frequency ultrasound is a promising alternate method to achieve a similar modulatory effect by partially attenuating the spleen-mediated inflammatory response in a noninvasive, low risk manner (Figs.…”

“…It has been previously demonstrated that splenectomy reduces inflammatory responses and prolongs survival in murine models of sepsis and septic shock, suggesting that targeting the activity of this lymphoid organ could be a valuable therapeutic adjunct. [12][13][14] A neural reflex has been identified, termed the cholinergic anti-inflammatory (CAP) pathway, which works on the spleen to inhibit inflammation and the production of proinflammatory cytokines. 15,16 This pathway can be stimulated pharmacologically with nicotinic agonists or by electrical stimulation of the vagus nerve.…”

A leukotriene-dependent spleen-liver axis drives TNF production in systemic inflammation

“…But a critical analysis of the literature reveals that the link between spleen and TNF production is far from firmly established. The chief piece of evidence linking spleen and TNF is that splenectomy drastically impairs the rise of TNF in the plasma of animals with systemic inflammation induced by bacterial lipopolysaccharide (LPS) or cecal perforation (9)(10)(11). This fact, however, does not necessarily imply that the spleen is the main source of circulating TNF, because it does not rule out the possibility that splenectomy could render other TNF-producing organs less responsive to inflammatory stimuli.…”