Splenic Regeneration Research Articles

Splenic enlargement induced by preoperative chemotherapy is a useful indicator for predicting liver regeneration after resection for colorectal liver metastases

BackgroundConversion chemotherapy may downsize unresectable colorectal liver metastases (CRLMs), but may cause liver injury and splenic enlargement. The effect of preoperative chemotherapy on liver regeneration after liver resection remains undetermined. The aim of this study was to examine whether splenic enlargement induced by preoperative chemotherapy is an indicator to identify high-risk patients for impaired liver regeneration and liver dysfunction after resection.MethodsWe retrospectively reviewed 118 Japanese patients with CRLMs. Fifty-one patients had conversion chemotherapy. The other 67 patients underwent up-front liver resection. We clarified effects of conversion chemotherapy on splenic volume, liver function, and postoperative liver regeneration. Perioperative outcome was also analyzed.ResultsA ratio of the splenic volume before and after chemotherapy (SP index) in the oxaliplatin-based chemotherapy group was significantly greater than other chemotherapy groups after 9 or more chemotherapy cycles. Patients whose SP index was 1.2 or more had significantly higher indocyanine green retention rate at 15 min (ICG-R15) than patients without chemotherapy. Analyses of covariance showed liver regeneration rate after resection was decreased in patients whose SP index was 1.2 or more. The incidence of postoperative liver dysfunction in patients whose SP index was 1.2 or more was significantly greater than patients without chemotherapy. Multivariate analysis showed SP index was a significant predictive factor of impaired liver regeneration.ConclusionsSplenic enlargement induced by preoperative chemotherapy was a useful indicator for impaired liver regeneration after resection and a decision-making tool of treatment strategy for unresectable CRLMs.

Expected Sonographic Appearance of the Spleen in Children and Young Adults With Sickle Cell Disease: An Update.

To update the imaging literature regarding spleen appearances in young patients with sickle cell disease (SCD). We conducted a retrospective study and included 112 patients age 0 to 21 years with SCD who had at least 1 abdominal sonogram at our institution between 1999 and 2011. Radiologic findings were compared between risk groups by χ(2) analysis. Findings were correlated with other imaging modalities when available. In our cohort, 35.7% of patients had autosplenectomy, and 8.0% had undergone surgical splenectomy. Only 5.0% of individuals age 0 to 5 years had autosplenectomy. In those who had not undergone surgical splenectomy or autosplenectomy, 76.2% had echogenic spleens, heterogeneous-appearing spleens, or both, and patients with the homozygous sickle cell anemia (HbSS) genotype were more likely to have an abnormal spleen echo texture. Patients treated with transfusions had echogenic spleens and had a higher frequency of splenic regeneration nodules. Most patients (80%) with splenomegaly did not require surgical splenectomy after 5.7 years of follow-up. Twenty years ago, children with HbSS SCD were expected to have autosplenectomy by age 5 years. There have been changes in the radiologic appearance of the spleen in patients with SDC, likely due to improved supportive care and the use of acute and chronic transfusion therapy. We found that autosplenectomy is rare by age 5 years, and during childhood and adolescence, the spleen typically appears echogenic, heterogeneous, or both, depending on disease severity.

Immunoexpression of proliferating cell nuclear antigen (PCNA) in spleen of splenectomized rats with preservation of inferior pole, submitted to hyperbaric oxygenation

To analyze PCNA immunoexpression on the inferior pole of the spleen of splenectomized rats submitted to hyperbaric oxygenation (HBO). Were analyzed fragments of the inferior pole of the spleen of 20 male Wistar rats submitted to splenectomy with preservation of the inferior pole. The rats were divided in two groups: group A (n=10) without HBO and group B (n=10) submitted to HBO at 2, 5 atmospheres per 120 minutes, twice a day for three days and once a day for seven days. The groups were then subdivided in four subgroups: A15 (n=5), with euthanasia on the 15th day; A45 (n=5), with euthanasia on the 45th day; B15 (n=5) with euthanasia on the 15th day and B45 with euthanasia on the 45th day. Respectively on these days, fragments of the inferior pole of the spleen of all animals were collected and analyzed with the immunohistochemistry technique in order to evaluate PCNA expression. There was an expressive increase in PCNA immunoreactivity in the group B. The 45 day postoperative period resulted in a higher level of positivity than the 15 day postoperative period (p<0.01). The quantitative analysis of proliferating cell nuclear antigen positive suggests that hyperbaric oxygenation increases cellular proliferation, contributing to splenic regeneration.

Partial Splenectomy for Hereditary Spherocytosis

Partial Splenectomy for Hereditary Spherocytosis

Partial splenectomy for hereditary spherocytosis: a multi-institutional review

Background/Purpose Partial splenectomy has emerged as a surgical option for selected children with hereditary spherocytosis, with the goal of reducing anemia while preserving splenic function. This multi-institutional study is the largest series to date examining outcomes data for partial splenectomy in patients with hereditary spherocytosis. Methods Data were collected retrospectively from 5 North American pediatric hospitals. Sixty-two children underwent partial splenectomy for hereditary spherocytosis between 1990 and 2008. Results At 1 year following partial splenectomy, mean hemoglobin significantly increased by 3.0 ± 1.4 g/dL (n = 52), reticulocyte count decreased by 6.6% ± 6.6% (n = 41), and bilirubin level decreased by 1.3 ± 0.9 mg/dL (n = 25). Patients with poor or transient hematologic response were found to have significantly more splenic regeneration postoperatively compared with patients with a durable clinical response (maximal spleen dimension, 9.0 ± 3.4 vs 6.3 ± 2.2 cm). Clinically significant recurrence of anemia or abdominal pain led to completion splenectomy in 4.84% of patients. No patients developed postsplenectomy sepsis. Conclusions Our multi-institutional review indicates that partial splenectomy for hereditary spherocytosis leads to sustained and clinically significant improvement in hematologic profiles and clinical symptoms in most patients. Our data support partial splenectomy as an alternative for selected children with hereditary spherocytosis.

Regeneration of Splenic Autotransplants Attached on Liver by a Tissue Adhesive

Background The regeneration of splenic autotransplants remains unsatisfactory. The liver has a rich blood supply and is prone to form collateral vessels to nearby ischemic tissues. It should be valuable to study whether it is a new site to facilitate splenic regeneration. Materials and Methods One hundred twenty Sprague-Dawley rats were randomly divided into 12 groups. After splenectomy, each weighed spleen was attached to the diaphragmatic side of the left hepatic lobe using an adhesive. The rats were sacrificed on postoperative day(POD)s 1, 3, 7, 14, 21, 28, 35, 42, 49, 56, 70, and 84. Six spleens in each group were dissected for weighing and another 4 for histologic analysis (H&E). Splenic autografts of another 12 rats attached to the mesenterium were sacrificed on POD 28, 56, and 84 for histologic analysis (H&E). Results The spleens attached to the liver underwent almost complete necrosis and then regenerated centripetally into structures comparable to a normal spleen, with typical red and white pulps as well as a marginal zone on POD 35. The mass of the implants recovered to more than two fifths of the original (44.2% ± 3.6%) on POD 84. For splenic autografts attached to mesenterium, typical red and white pulps were observed on POD 56. The marginal zone was not clear on POD 84. Conclusion The liver proved to be an appropriate site for splenic autotransplantation. Regeneration was histologically superior to that of splenic tissue attached to the mesenterium. The application of a tissue adhesive may be a new technique for splenic autotransplantation.

Pancreatic Duct Disruption With Autosplenectomy

Question: A 64-year-old male patient visited our cardiovascular outpatient department for regular follow-up for hypertension and coronary artery disease on July 24, 2008. Hypotension was noted; his systolic and diastolic blood pressure of 89 and 34 mmHg, respectively. So he was referred to our emergent department (ED) for further evaluation. According to his previous medical records, he had a past history of gallbladder stones inducing acute pancreatitis with pseudocyst formation over the pancreatic tail region, which was initially managed by pigtail tube drainage initially on March 21, 2008 (Figure A). Endoscopic retrograde cholangiopancreatography (ERCP) revealed pancreatic duct disruption on April 25, 2008. Hence, endoscopic papillotomy, common bile duct stone extraction and 7-French (Fr) plastic stent pancreatic duct insertion were subsequently performed. Antibiotics were prescribed and the patient was examined by abdominal sonography every week until the pseudocyst completely resolved. The pigtail drainage tube was removed when there was no further drainage and he was discharged on July 3, 2008. In our ED, the physical examination did not reveal any fever, abdominal pain, jaundice, or other specific discomfort. Blood counts were as follows: white blood cell 32,900/mm3 (normal, 4800–10,800/mm3); hemoglobin, 12.5 g/dL (normal, 12–16); and platelets, 613,000/mm3 (normal, 130,000–400,000/mm3). The differential count of white blood cell was neutrophils, 74%; lymphocyte, 19%; monocyte, 7%; eosinophils, 0%; and basophils, 0%. Serum biochemistry test results were as follows: alanine aminotransferase, 78 IU/L (normal, 0–40); alkaline phosphatase, 175 U/L (normal, 10–100); γ-glutamyltransferase, 223 U/L (normal, 8–61); total bilirubin, 0.4 mg/dL (normal, 0.2–1.6); C-reactive protein, 11.79 mg/dL (normal, 0–0.5); and amylase, 218 U/L (normal, <180). An abdominal computed tomography (CT) scan in our ED is shown in Figures B and C. Pigtail drainage and antibiotics treatment were given immediately. A pus-like discharge was found from the pig-tail drainage tube. What is the possible diagnosis? See the Gastroenterology web site (www.gastrojournal.org) for more information on submitting your favorite image to Clinical Challenges and Images in GI. Under the impression that the patient had persistent pancreatic duct disruption with autosplenectomy, ERCP was performed and the 7-Fr internal stent was replaced by an 8-Fr stent to decrease pancreatic duct pressure. The pigtail drainage tube was reimplanted from the pseudocyst to the pancreatic tail duct and gradually changed to a smaller size. However, persistent leukocytosis and thrombocytosis without clinical evidence of infectious disease were noted during this hospitalization. We consulted a hematologist and genetic studies showed mixed polyclonal blood cell counts. Hence, lymphoproliferative disease was less likely. Consequently, both functional and anatomic destruction of the spleen were highly suspected. Follow-up ERCP on October 22, 2008, disclosed a healed pancreatic duct (Figure D). Therefore, the external drainage tube was removed smoothly. Follow-up CT scan disclosed no recurrence of the pseudocyst and mild regeneration of spleen on February 22, 2009 (Figure E). The final diagnosis was pancreatic duct disruption with persistent pancreatic fluid leakage and splenic autodigestion. Autosplenectomy has been reported in a number of diseases, such as sickle cell anemia, idiopathic thrombocytopenic purpura, systemic lupus erythematosus, rheumatoid arthritis, celiac disease, amyloidosis, and splenic irradiation.1Caro J. Hypersplenism and hyposplenism.in: Lichtman M.A. Beutler E. Kipps T.J. Williams hematology. 7th ed. McGraw-Hill Medical, New York2006Google Scholar In acute pancreatitis, pseudocyst direct invasion or splenic vessel thrombosis with subsequent liquefaction of a splenic infarction are the causes of splenic parenchymal destruction.2Hastings O.M. Jain K.M. Khademi M. et al.Intrasplenic pancreatic pseudocyst complicating severe acute pancreatitis.Am J Gastroenterol. 1978; 69: 182-186PubMed Google Scholar In this case, CT scan disclosed pancreatic tail and splenic abscess without pseudocyst formation or splenic vessel thrombosis. Therefore, autosplenectomy was caused by persistent pancreatic fluid leak and local abscess formation. This case also disclosed mild splenic regeneration after autodigestion. Splenic autodigestion should be taken into consideration when duct disruption occurs at pancreatic tail. Acute pancreatitis with splenic involvement often required aggressive treatment, including repeated percutaneous drainage, pancreatectomy, and/or splenectomy.3Heider R. Behrns K.E. Pancreatic pseudocysts complicated by splenic parenchymal involvement: results of operative and percutaneous management.Pancreas. 2001; 23: 20-25Crossref PubMed Scopus (38) Google Scholar Although splenic autodigestion is rare, it may be lethal if undiagnosed. Clinicians should maintain a high index of suspicion of splenic autodigestion when patients had acute pancreatitis history with persistent leukocytosis and thrombocytosis.

Splenic regeneration following splenectomy and impact on sepsis: a clinical review

The spleen is a large lymphoid intra‐abdominal organ. It is involved in immunological response, removal of particulate matter and aged or defective blood cells from the circulation.1 Correlation between splenectomy, infection risk and overwhelming sepsis was first reported over 50 years ago.2 The incidence of post‐splenectomy sepsis has been investigated and at‐risk patients stratified. Lowest infection rates have been reported in traumatic splenectomy patients and the highest in those with haematological disorders.3 Given the overall significant risk of post‐splenectomy sepsis, all such patients receive prophylaxis irrespective of the surgical indication. Current guidelines include antibiotic prophylaxis, immunization against pneumococci, meningococci, haemophilus influenza and flu vaccine. Patients need urgent hospital admission if overcome by serious infection and carry health warnings.4 These necessary steps have an obvious impact on their lifestyle. Splenectomy used to be the only surgical option for trauma patients suffering splenic injuries. In the past two decades the concept of spleen conservation has been widely accepted in selected patients and positive outcomes are reported.5,6 However patients with severe parenchymal tears, active intraabdominal bleeding and complete splenic fragmentation will still require surgery and often will need a splenectomy.7 In this review we studied the role of splenosis and spleen autotransplantation in patients who suffer splenic trauma and their possible protective role on post‐splenectomy sepsis.

Functional and anatomic correlation of splenic regeneration following embolization

Functional and anatomic correlation of splenic regeneration following embolization

Tissue-Engineered Spleen Protects Against Overwhelming Pneumococcal Sepsis in a Rodent Model

Solid organs production is an ultimate goal of tissue engineering. After refining a technique for intestinal engineering, we applied it to a solid organ, the spleen. Overwhelming postsplenectomy sepsis results in death in nearly half of all cases. This risk is pronounced in children. Necrosis of autotransplanted spleen slices occurs prior to regeneration. We postulate that tissue engineering techniques might be superior. Four groups of Lewis rats were compared: sham laparotomy, tissue-engineered spleen (TES), traditional spleen slices, and splenectomy. TES was generated from splenic units, multicellular components of juvenile spleen implanted on a biodegradable polymer scaffold, and spleen slices were derived from age-matched juveniles. Pneumococcal sepsis was induced at wk 16, and survival curves were constructed. Tissue-engineered spleen protected against pneumococcal septicemia with a survival proportion of 85.7% compared with 41.17% of splenectomized animals. Spleen slice was also protective with 71.43% survival. Compared with splenectomy, control and TES groups were statistically significant (P = 0.0002, P = 0.0087; hazard ratio of splenectomy = 5.493) and the Slice group was nearly statistically significant (P = 0.0642, hazard ratio of splenectomy = 2.673). TES is a novel application of tissue engineering to splenic regeneration and creates a functional spleen. This approach could be advantageous in severe pediatric trauma.

Splenic Artery Embolization for Non-Bleeding Gastric Varices and Hypersplenism Due to Isolated Splenic Vein Thrombosis

Splenic artery embolization has been used with success for treatment of bleeding gastric varices secondary to splenic vein thrombosis. We present a case of isolated splenic vein thrombosis causing non-bleeding gastric varices and hypersplenism which was successfully treated with splenic artery embolization. A 56 year old man with hemachromatosis previously treated with phlebotomy presented with intermittent epigastric abdominal pain and thrombocytopenia. The subsequent workup included an evaluation for cirrhosis and portal hypertension including a liver biopsy and hepatic wedge pressure measurements which were normal. Further evaluation included a normal bone marrow biopsy. A CT scan and duplex ultrasound revealed an enlarged spleen of 15 cm as well as a suggestion of gastric varices and nonvisualization of the splenic vein. Splenic vein thrombosis was confirmed by MR venogram. Hematological evaluation revealed no hypercoagulable state and there was no history of pancreatitis or other explanation for the isolated finding of splenic vein thrombosis. Subsequently, an EGD revealed significant gastric varices. It was decided that a surgical splenectomy would be high risk due to multiple abdominal venous collaterals and that a medical splenectomy with splenic artery embolization is indicated to decompress venous collaterals prior to a planned surgical splenectomy. After the embolization, follow-up endoscopies have shown improvement in gastric varices and repeat laboratory evaluation has shown normalization of platelet counts even after ten months of follow-up. The decision was made not to proceed with surgical splenectomy at this time. There are only a few reported cases of isolated splenic vein thrombosis without a clear etiology. Splenic vein thrombosis is well known to cause hypersplenism and gastric varices. Splenic artery embolization has been described for 25 years and is mainly utilized in patients with bleeding gastric varices and hypersplenism, usually prior to splenectomy. This procedure is traditionally reserved for high risk surgical patients as it has been reported to have complications such as hematoma or splenic abscess. We suggest this procedure as an effective treatment modality while monitoring clinically for complications or evidence of splenic regeneration at which time surgical therapy could be considered.

Failure of partial splenectomy to ameliorate the anemia of pyruvate kinase deficiency

The authors report a case of pyruvate kinase deficiency in a 4-year-old patient who required monthly blood transfusions. A partial splenectomy was performed to decrease the transfusion requirements and at the same time preserve splenic function. After removal of 80% of splenic tissue there was no amelioration of her transfusion needs. She responded well to subsequent total splenectomy performed 6 months later, and is currently well and transfusion independent. Rapid splenic regeneration possibly caused by erythrophagocytosis and extramedullary hematopoiesis is the presumed reason for this patient's failure to respond to partial splenectomy.

First Report of Reversal of Organ Dysfunction in Sickle Cell Anemia by the Use of Hydroxyurea: Splenic Regeneration

Much of the morbidity associated with sickle cell anemia (SCA) is due to ongoing infarction resulting in organ dysfunction. Because the spleen is often the first organ damaged in this illness, there is a significant impairment of the immune system in these patients. Hydroxyurea (HU) has been shown to increase fetal hemoglobin (HbF) and decrease painful episodes in patients with this disease. It is unclear whether HU can prevent organ damage. We treated two SCA patients with HU for several years and found evidence of reversal of previously documented splenic dysfunction. Patient no. 1 was treated for 30 months with an increase in HbF to 30%. HU was stopped because of cytopenia. She developed left upper quadrant pain. A splenectomy was performed due to the possibility of splenic abscesses. A pathologic review found no evidence of infection and an enlarged spleen that showed active germinal centers. Patient no. 2 was treated for 24 months with HU before developing splenomegaly. His HbF levels were 25% to 30%, his pit counts averaged 2%, and his liver spleen scans showed uptake. These two cases show that chronic HU therapy may reverse splenic dysfunction in certain patients and suggest that this drug may have efficacy beyond the elimination of pain in SCA.

The effects of experimental splenic autotransplantation and imipenem-cilastatin treatment in postsplenectomy Pseudomonas aeruginosa sepsis.

Male Wistar albino rats were allocated to three groups-sham operated (n: 10), splenectomized (n: 20) and splenic autotransplanted (n: 10). Twelve weeks after operation, all were challenged with 1.8 x 10(8) cfu/ml Pseudomonas aeruginosa intranasally. Half of the splenectomized rats received imipenem-cilastatin after 2 h of bacterial challenge. Mortality was then observed for the next 12 days. All animals were autopsied and liver, kidney, spleen and lung specimens were processed for microbiological culture and histopathological examination. In 80% of autotransplanted rats, splenic tissue regeneration was histopathologically verified. Hemoglobin oxidation of erythrocytes increased in splenectomized rats and remained close to control levels in the autotransplanted group. No significant difference was detected between IgM levels of splenectomized and autotransplanted groups. Mortality rates were the same for all groups, except that splenectomized animals given antimicrobial therapy had increased survival rates. In conclusion, it is likely that the spleen has no role in protection against pulmonary sepsis and that only appropriate antimicrobial therapy can protect the splenectomized host from Pseudomonas sepsis.

Regeneration of splenic stromal elements.

Splenic regeneration represents an interesting phenomenon both in relation to its role as a model system (to study the development of the complex three-dimensional architecture of an immunological organ) and because of the clinical application, namely autotransplantation of spleen. The latter is one of the attempts to restore splenic functions after splenectomy, which is known to increase a life-long risk of fatal sepsis. However, splenic functions of autotransplanted splenic tissue are known to be highly dependent on the recovery of the complex microenvironment and immunoarchitecture of the splenic compartments during the regeneration processes, but the elements inducing splenic reorganization are still unknown. Therefore, the present work investigates whether splenic stroma depleted of cells is able to induce regenerative processes after implantation. In addition, we tried to recombine stromal tissue with selected cell populations to study their influence. Cell-free stromal tissue induced angiogenesis and to a lesser extent also attracted the immigration of lymphocytes during the first 60 days of regeneration. However, after this period of regeneration, the transplants began to degenerate and were resorbed. The recombination of stromal tissue with mitogen-stimulated spleen cells only resulted in intensifying the degenerative processes, and all implants were resorbed after 120 days. Except that in the first 30 days there were some accumulations of lymphocytes that resembled primitive follicles, no splenic compartments such as red pulp, periarteriolar lymphoid sheath, or marginal zone could be detected in any of the transplants. From these results it can be concluded that splenic stroma can induce the primary events of splenic regeneration (like angiogenesis), but is not able to provide an appropriate microenvironment and immunoarchitecture for a correct repopulation and differentiation of cells. Furthermore, the recombination experiments point to a minor role of T-cells and possibly an important role for accessory cells in splenic regeneration.

Splenic regeneration does not occur after sub-total splenectomy

The case of a 6-year-old male undergoing sub-total splenectomy after a trivial fall is described. Although the remaining spleen survived, no increase in splenic bulk had occurred 8 years later as measured by isotope scan.

Dynamic Change of the Vascular Wall from Transmural to Intercellular Passage of Red Blood Cells Observed in Splenic Regeneration

Rat splenic tissues were autotransplanted into the major omentum, and the operated animals were treated with phenylhydrazine to investigate the passage of erythrocytes through the vascular wall during splenic regeneration. Both ways of the passage were differentiated during regeneration. From day 1 to day 5 after transplantation, the pores were formed in the endothelial cells, through which erythrocytes (chiefly reticulocytes) migrated, and were closed by the basal lamina when erythrocytes did not penetrate. From day 7 to day 10, endothelial cells proliferated, and some of them were transformed into sinus endothelial cells containing condensed microfilaments and formed the interendothelial slit, but few erythrocytes passed there at this stage yet. On and after day 11, when the sinus endothelial cells exhibited well-developed microfilaments, reticular cells contained moderately developed microfilaments and the basal lamina developed well, the slits were opened, where a large number of erythrocytes passed. These results showed, concerning the passage of blood cells, that the vascular wall in the splenic autografts changed from the transmural pattern to the intercellular one after a marked proliferation of endothelial cells and that the effective passage of erythrocytes was closely associated with the development of microfilaments in the cytoplasm of endothelial cells and basal lamina as well as the interaction of reticular cells.

Splenic autotransplantation in nude mice

Splenic fragments were autotransplanted into the greater omentum of nude mice (nu/nu) and normal mice to investigate the formation of white pulp in splenic regeneration. The formation of white pulp began from day 5 after transplantation in both groups. Two patterns were found. In one pattern, follicles containing only B cells were first formed and developed into white pulp with poorly developed periarterial lymphoid sheaths (PALS). Most of the white pulp in nude mice and about one third of white pulp formed at day 28 in normal mice followed this pattern. In the second pattern, PALS were first formed and afterwards follicles appeared in the periphery of PALS. This was mainly seen in normal mice. Thus splenic autografts in normal mice contain white pulp with poorly developed PALS, and the homing of T cells begins later than that of B cells. This suggests the possibility of incomplete cellular immunity.

Ultrastructural study on endothelial cells in splenic autotransplantation

AbstractThe splenic tissue of the rat was autotransplanted into the greater omentum to investigate the angiogenic process during splenic regeneration. Chronological observations showed the following two stages. Initially surviving subcapsular sinus endothelial cells migrated to form a preliminary vascular network, which anastomosed with ingrowing omental capillaries to form a circulatory system. In this way, splenic autotransplants would not undergo necrosis and would rapidly form endothelial and reticular cells. At a later stage, the preliminary vascular network differentiated into arteries (arterioles, capillaries), splenic sinuses, and veins. Marked morphologic changes occurred in the endothelial cells, such as vacuole formation, fenestration, and the condensation of intraendothelial microfilaments, resulting in interendothelial slits. These results showed that the formation of a preliminary vascular network caused distinct splenic regeneration and that splenic autotransplantation is a suitable model to study angiogenesis in vivo.

異所性のひ再生における間質細胞の役割とろ胞樹枝状細胞の起源について

A subcutaneous splenic implantation study was carried out using BALB/c, C57BL/6 and their F1 mice. The frequency of heterotopic splenic regeneration under several conditions was evaluated 3 months after the implantation. An immunohistochemical examination with anti-H-2Dd and H-2Db monoclonal antibodies was employed to analyze the derivation of the cells constituting regenerated graft tissues. A large number of the implants regenerated when the parental spleens were grafted to F1, when BALB/c and C57BL/6 spleens were grafted to F1, and when cyclophosphamide-treated BALB/c spleens were grafted to F1. A very small number of the implants from lethally irradiated BALB/c regenerated on F1. All splenic implants of F1 to parental mice were rejected, but when the parental grafts which had regenerated on F1 were re-implanted to the original strain of mice, more than 50% of them regenerated. The H-2 immunohistochemical examination revealed that most hematogenic cells of the parental grafts that regenerated on F1 were replaced by F1 host type, but the stromal cells such as endothelial cells, reticulum cells of the white pulp and connective tissue cells of the trabecula were of the doner type. The H-2 immunophenotype of follicular dendritic cells in these grafts were also of the doner (parental) type. These results indicate that requirement of the implant derived stromal cells for the heterotopic splenic regeneration, and that the cell lineage of follicular dendritic cells as non-immigrating stromal cells.