.Journal of Neuroimmunology 88 1998 67–76 Regeneration of implanted splenic tissue in the rat: re-innervation is host age-dependent and necessary for tissue development

The loss of spleen may lead to fatal bacterial infections. To prevent this, splenic autotransplantation has been performed in humans and experimental animals. However, there is still controversy about the protective function of this procedure. Since innervation plays an important role in splenic function, we investigated whether splenic regenerates are re-innervated, and whether this depends on the donor . . .and host age. Splenic tissue 30 mg was implanted into the greater omentum of either young 2 days or old 12 months rats, from either young or old syngeneic animals. After 3 months of regeneration, the weight of the regenerates was determined, PGPq nerve fibers were q q. q q.revealed by immunohistology, and subdivided into nerve fibers of sympathetic TH, NPY or sensory SP, CGRP origin. In q. q.addition, proliferating Ki-67 proliferation antigen and apoptotic cells TUNEL technique were likewise investigated. No innervation of splenic regenerates was observed after implantation into old hosts, correlating with poorly developed splenic compartments. In contrast, almost normal re-innervation occurred in young hosts after implantation of both young and old splenic tissue. These regenerates showed well-developed splenic compartments and a normal number and tissue distribution of proliferating and apoptotic cells. However, .after the implantation of young tissue, the final size of splenic regenerates was three times larger 140"30 vs. 40"10 mg. Thus, re-innervation of splenic implants is necessary for their subsequent development. It is determined by host age, whereas the final size of the splenic regenerates is regulated by donor age-dependent factors. This model is useful for studying both the process leading to initia