Reimmunization and splenic autotransplantation: A long-term study of immunologic response and survival following pneumococcal challenge

Splenic autografts have phagocytic function and increase survival after experimental sepsis. The long-term effect of transplant viability, phagocytic capacity, and immunologic responsiveness were evaluated. Rats were divided into experimental groups: control, splenectomized, and splenic autotransplant rats. Approximately one-half of the rats were immunized against pneumococcus. Twelve months later, the rats were reimmunized, and the pneumococcal antibody titers were measured. The effect of operation and immunization was determined by challenging rats with intravenously administered pneumococci. Bacterial clearance from the bloodstream was measured and mortality recorded. Spleens were weighed and examined histologically. In unimmunized rats, pneumococcus was cleared from the bloodstream of control rats, whereas splenectomized and splenic autotransplant rats demonstrated a progressive increase of pneumococci in the bloodstream. However, splenic autotransplant rats grew fewer bacteria after challenge (P < 0.05). All control rats survived. Thirty-three percent of splenic autotransplant rats were alive, but significantly fewer splenectomized rats (6%) survived (P < 0.05). After reimmunization, highest antibody titers were noted in control rats (P < 0.05). Splenic autotransplant rats had higher antibody titers than did splenectomized rats (P < 0.05). Reimmunized splenic autotransplant rats had greater survivorship (71%) when compared with reimmunized splenectomized rats (26%) (P < 0.003). At 1 year, transplants were smaller than control spleens (P < 0.001), although histologic integrity was maintained. Splenic autotransplantation results in better phagocytic function, improved response to reimmunization, and increased survival after pneumococcal challenge and may be an important measure in preventing postsplenectomy sepsis.