The role of the spleen and splenic autotransplants in clearing experimental bacteremia caused by the gram-negative bacterium Escherichia coli.

Several clinical and laboratory studies have demonstrated the risk of sepsis in connection with encapsulated bacteria. The importance of clearing these organisms by the spleen is now well accepted. In contrast, the present work deals with the clearance of non-encapsulated gram-negative bacteria (Escherichia coli). The animals used for the experiments (a heterogeneous population of rabbits) were divided into a control group, a splenectomized group, and an autotransplanted group. The histological examination of the splenic transplants revealed typical splenic tissue including lymphatic follicles with germinal activity 42 days after transplantation. For estimation of the clearance capacity different amounts of bacteria were injected i.v. into the rabbits, and colony-forming bacterial cells in the blood were counted at certain intervals. In the control group no bacteria could be detected in the blood after 7 min. All animals of the splenectomized and autotransplanted groups showed a remarkable decrease in clearance efficiency (no bacteria in the blood after 19 min). No difference in the clearance kinetics could be shown between splenectomized and autotransplanted animals. Measuring the uptake of bacterial cells into different organs elicited low incorporation in the spleen as compared to non-immunocompetent organs, but no difference between normal spleen and splenic replants. However, saturation with E. coli cells reached higher limits in the normal spleen than in autotransplants. The immunologic capacity with respect to IgM-producing lymphocytes was measured by the hemolytic plaque assay. The results showed a severe malfunction of the autotransplants as compared to the normal spleen (only 2% of the activity of the control group). Vaccination against E. coli increased the clearance efficiency in all three groups. The data presented in this paper point out that several functions of the spleen cannot be carried out by autotransplants. The reasons, therefore, may be limited transplant mass and/or decreased specific functions.