Preservation of splenic tissue prevents postsplenectomy pulmonary sepsis following bacterial challenge

Previous studies utilizing an intravenous method of bacterial challenge have failed to demonstrate a protective effect of reimplanted splenic tissue. This method of intravenous bacterial challenge bypasses the lungs, the usual portal of entry in postsplenectomy sepsis. In this study a method of bacterial challenge via the lung was used to investigate the ability of splenic tissue to protect against postsplenectomy sepsis. For this purpose 203 rats were divided into four groups: total splenectomy, hemisplenectomy, sham-operated controls, and nonoperated controls. Two weeks postoperatively all rats were challenged with either 1 × 10⁵ or 5 × 10⁶ Streptococcus pneumoniae delivered via transtracheal injection. Mortality rates were observed for 2 weeks. At the lower dose of bacteria, no difference in mortality was observed among all treatment groups. Similarly there was no difference in 14-day mortality at the larger bacterial dose. At the higher challenge dose, however, there was a significant difference in early mortality (Days 1-9) between the total splenectomy group (100% mortality) and the other three groups (control 38%, sham control 25%, hemisplenectomy 25%). There was no difference in mortality between the hemisplenectomy group and the two control groups. Unlike the intravenous method of challenge, transtracheal challenge does not bypass the pulmonary host-defense system, thus allowing interaction of splenic-derived tuftsin and antibody with pulmonary-derived neutrophils and macrophages, and provides a more suitable model for the study of postsplenectomy spesis. Splenectomy was shown to result in a higher early mortality due to pulmonary sepsis, whereas preservation of at least half the spleen reduced the early mortality due to pulmonary sepsis.