The Influence of the Spleen on Neutrophil Apoptosis in Vivo

Splenectomy is associated with altered leukocyte kinetics after severe trauma

BACKGROUND

Inadequate activation of the innate immune system after trauma can lead to severe complications such as Acute Respiratory Distress Syndrome and Multiple Organ Dysfunction Syndrome. The spleen is thought to modulate the cellular immune system. Furthermore, splenectomy is associated with improved outcome in severely injured trauma patients. We hypothesized that a splenectomy alters the cellular immune response in polytrauma.

METHODS

All adult patients with an ISS ≥ 16 and suffering from splenic or hepatic injuries were selected from our prospective trauma database. Absolute leukocyte numbers in peripheral blood were measured. White blood cell kinetics during the first 14 days were compared between splenectomized patients, patients treated surgically for liver trauma and nonoperatively treated individuals.

RESULTS

A total of 129 patients with a mean ISS of 29 were included. Admission characteristics and leukocyte numbers were similar in all groups, except for slightly impaired hemodynamic status in patients with operatively treated liver injuries. On admission, leukocytosis occurred in all groups. During the first 24 h, leukopenia developed gradually, although significantly faster in the operatively treated patients. Thereafter, leukocyte levels normalized in all nonoperatively treated cases whereas leukocytosis persisted in operatively treated patients. This effect was significantly more prominent in splenectomized patients than all other conditions.

CONCLUSIONS

This study demonstrates that surgery for intra-abdominal injuries is associated with an early drop in leucocyte numbers in peripheral blood. Moreover, splenectomy in severely injured patients is associated with an altered cellular immune response reflected by a persistent state of prominent leukocytosis after trauma.

Why the spleen is a very rare site for metastases from epithelial cancers

It is not known why metastases from epithelial cancers are rare in the spleen, yet common in the other major organs of the reticuloendothelial system in which, like the spleen, leucocytes display a prolonged physiological intravascular transit time. Another unresolved issue that at first seems unrelated to splenic metastases is the inconsistency between the concept of physiological granulocyte disposal through granulocyte ageing and the observation that granulocytes leave the blood in an exponential fashion (half-time 7 h), which implies random disposal. Intravascular granulocytes pass through the spleen with an exponential distribution of transit times (mean 10 min). The spleen is highly active in physiological granulocyte destruction so it is suggested that the variation in times of exposure to the splenic microenvironment converts the age-dependent granulocyte destruction observed ex vivo into the random process observed in vivo, probably through exposure to apoptosis-inducing signals. This leads to the second hypothesis, which is that cancer cells fail to survive in the spleen as a result of these pro-apoptotic signals.