Immunoarchitecture of regenerated splenic and lymph node transplants

Autogenic splenic implantation versus splenectomy in patients undergoing distal pancreatectomy for benign or low-grade malignant lesions of the distal pancreas: study protocol for a multicentre, open-label, randomized controlled trial (RESTORE)

BACKGROUND

The spleen plays a significant role in the clearance of circulating microorganisms. Sequelae of splenectomy, especially immunodeficiency, can have a deleterious effect on a patient's health and even lead to death. Hence, splenectomy should be avoided and spleen preservation during elective surgery has become a treatment goal. However, this cannot be achieved in every patient due to intraoperative technical difficulties or oncological reasons. Autogenic splenic implantation (ASI) is currently the only possible way to preserve splenic function when a splenectomy is necessary. Experience largely stems from trauma patients with a splenic rupture. Splenic immune function can be measured by the body's clearing capacity of encapsulated bacteria. The aim of this study is to assess the splenic immune function after ASI was performed during minimally invasive (laparoscopic or robotic) distal pancreatectomy with splenectomy.

METHODS

This is the protocol for a multicentre, randomized, open-labelled trial. Thirty participants with benign or low-grade malignant lesions of the distal pancreas requiring minimally invasive distal pancreatectomy and splenectomy will be allocated to either additional intraoperative ASI (intervention) or no further intervention (control). An additional 15 patients who will undergo spleen-preserving distal pancreatectomy serve as the control group with normal splenic function. Six months postoperatively, after assumed restoration of splenic function, patients will be given a Salmonella typhi (Typhim Vi™) vaccine. The Salmonella typhi vaccine is a polysaccharide vaccine. The specific antibody titres immediately before and 4 to 6 weeks after vaccination will be measured. The ratio between pre- and post-vaccination antibody count is the primary outcome measure and secondary outcome measures include intraoperative details, length of hospital stay, 30-day mortality and morbidity.

DISCUSSION

This study will investigate the splenic immune function of patients who undergo ASI during minimally invasive distal pancreatectomy with splenectomy. The splenic immune function will be measured using the surrogate outcome of specific antibody titre after vaccination with a Salmonella typhi vaccine. The results will reveal details about splenic function after ASI and guide further treatment options for patients when a splenectomy cannot be avoided. It might eventually lead to a new standard of care making sometimes more demanding and time-consuming spleen-preserving procedures redundant.

TRIAL REGISTRATION

International Standard Randomized Controlled Trials Number (ISRCTN) ISRCTN10171587. Prospectively registered on 18 February 2019.

Spleen: Reparative Regeneration and Influence on Liver

This review considers experimental findings on splenic repair, obtained in two types of small animal (mouse, rat, and rabbit) models: splenic resections and autologous transplantations of splenic tissue. Resection experiments indicate that the spleen is able to regenerate, though not necessarily to the initial volume. The recovery lasts one month and preserves the architecture, albeit with an increase in the relative volume of lymphoid follicles. The renovated tissues, however, exhibit skewed functional profiles; notably, the decreased production of antibodies and the low cytotoxic activity of T cells, consistent with the decline of T-dependent zones and prolonged reduction in T cell numbers. Species-specific differences are evident as well, with the post-repair organ mass deficiency most pronounced in rabbit models. Autotransplantations of splenic material are of particular clinical interest, as the procedure can possibly mitigate the development of post-splenectomy syndrome. Under these conditions, regeneration lasts 1-2 months, depending on the species. The transplants effectively destroy senescent erythrocytes, assist in microbial clearance, and produce antibodies, thus averting sepsis and bacterial pneumonia. Meanwhile, cellular sources of splenic recovery in such models remain obscure, as well as the time required for T and B cell number reconstitution.

The pig as a model for immunology research

The pig is an omnivorous, monogastric species with many advantages to serve as an animal model for human diseases. There are very high similarities to humans in anatomy and functions of the immune system, e g., the presence of tonsils, which are absent in rodents. The porcine immune system resembles man for more than 80% of analyzed parameters in contrast to the mouse with only about 10%. The pig can easily be bred, and there are less emotional problems to use them as experimental animals than dogs or monkeys. Indwelling cannulas in a vein or lymphatic vessel enable repetitive stress-free sampling. Meanwhile, there are many markers available to characterize immune cells. Lymphoid organs, their function, and their role in lymphocyte kinetics (proliferation and migration) are reviewed. For long-term experiments, minipigs (e.g., Göttingen minipig) are available. Pigs can be kept under gnotobiotic (germfree) conditions for some time after birth to study the effects of microbiota. The effects of probiotics can be tested on the gut immune system. The lung has been used for extracorporeal preservation and immune engineering. After genetic modifications are established, the pig is the best animal model for future xenotransplantation to reduce the problem of organ shortage for organ transplantation. Autotransplantation of particles of lymphnodes regenerates in the subcutaneous tissue. This is a model to treat secondary lymphedema patients. There are pigs with cystic fibrosis and severe combined immune deficiency available.

Determinants of postnatal spleen tissue regeneration and organogenesis

The spleen is an organ that filters the blood and is responsible for generating blood-borne immune responses. It is also an organ with a remarkable capacity to regenerate. Techniques for splenic auto-transplantation have emerged to take advantage of this characteristic and rebuild spleen tissue in individuals undergoing splenectomy. While this procedure has been performed for decades, the underlying mechanisms controlling spleen regeneration have remained elusive. Insights into secondary lymphoid organogenesis and the roles of stromal organiser cells and lymphotoxin signalling in lymph node development have helped reveal similar requirements for spleen regeneration. These factors are now considered in the regulation of embryonic and postnatal spleen formation, and in the establishment of mature white pulp and marginal zone compartments which are essential for spleen-mediated immunity. A greater understanding of the cellular and molecular mechanisms which control spleen development will assist in the design of more precise and efficient tissue grafting methods for spleen regeneration on demand. Regeneration of organs which harbour functional white pulp tissue will also offer novel opportunities for effective immunotherapy against cancer as well as infectious diseases.

Growth of Murine Splenic Tissue Is Suppressed by Lymphotoxin β-Receptor Signaling (LTβR) Originating from Splenic and Non-Splenic Tissues

Development and maintenance of secondary lymphoid organs such as lymph nodes and spleen essentially depend on lymphotoxin β-receptor (LTβR) signaling. It is unclear, however, by which molecular mechanism their size is limited. Here, we investigate whether the LTβR pathway is also growth suppressing. By using splenic tissue transplantation it is possible to analyze a potential contribution of LTβR signaling inside and outside of the implanted tissue. We show that LTβR signaling within the endogenous spleen and within non-splenic tissues both significantly suppressed the regeneration of implanted splenic tissue. The suppressive activity positively correlated with the total number of LTβR expressing cells in the animal (regenerate weights of 115 ± 8 mg in LTβR deficient recipients and of 12 ± 9 mg in wild-type recipients), affected also developed splenic tissue, and was induced but not executed via LTβR signaling. Two-dimensional differential gel electrophoresis and subsequent mass spectrometry of stromal splenic tissue was applied to screen for potential factors mediating the LTβR dependent suppressive activity. Thus, LTβR dependent growth suppression is involved in regulating the size of secondary lymphoid organs, and might be therapeutically used to eradicate tertiary lymphoid tissues during autoimmune diseases.

Lentinula edodes (shiitake) modulates chemically induced mutagenesis by enhancing pitting

This study was undertaken to understand how Lentinula edodes modulates in vivo mutagenesis induced by alkylating agents in bone marrow and peripheral blood as described in our previous article. Male Swiss mice were pretreated for 15 consecutive days with aqueous extracts prepared from L. edodes, after which, the number of circulating blood cells, normal erythroid bone marrow cell cycling, and phagocytosis of micronucleated reticulocyte (MNRET) and activation of spleen macrophages were assessed. The results indicate that the antimutagenicity seen in bone marrow and peripheral blood is exerted by distinct compounds with different actions. The antimutagenic effect in bone marrow is exerted by compounds subject to degradation at deep-freeze storage temperature of -20°C. On the other hand, compounds responsible for antimutagenicity in peripheral blood are not subject to degradation at -20°C. The results also indicate that the antimutagenic action in peripheral blood leading to the reduction of circulating MNRET occurs in the spleen primarily through a phagocytic activity due to higher macrophage numbers and probably not due to the enhanced activation state of individual cells.

TNF receptor-1 is required for the formation of splenic compartments during adult, but not embryonic life

Lymphotoxin β-receptor (LTβR) and TNF receptor-1 (TNFR1) are important for the development of secondary lymphoid organs during embryonic life. The significance of LTβR and TNFR1 for the formation of lymphoid tissue during adult life is not well understood. Immunohistochemistry, morphometry, flow cytometry, and laser microdissection were used to compare wild-type, LTβR(-/-), TNFR1(-/-) spleens with splenic tissue that has been newly formed 8 wk after avascular implantation into adult mice. During ontogeny, LTβR is sufficient to induce formation of the marginal zone, similar-sized T and B cell zones, and a mixed T/B cell zone that completely surrounded the T cell zone. Strikingly, in adult mice, the formation of splenic compartments required both LTβR and TNFR1 expression, demonstrating that the molecular requirements for lymphoid tissue formation are different during embryonic and adult life. Thus, interfering with the TNFR1 pathway offers the possibility to selectively block the formation of ectopic lymphoid tissue and at the same time to spare secondary lymphoid organs such as spleen and lymph nodes. This opens a new perspective for the treatment of autoimmune and inflammatory diseases.

Mesenteric lymph nodes are not required for an intestinal immunoglobulin A response to oral cholera toxin

Stimulation of the adaptive immune system in the gut is thought to be mainly initiated in the Peyer's patches as well as in the mesenteric lymph nodes (mLNs) and results in immunoglobulin A (IgA) secretion by plasma cells in the lamina propria. However, the precise role of the mLNs in the development of IgA immune responses is poorly understood. Thus, cholera toxin (CT) was administered to mLN-resected and mLN-bearing animals and the IgA response to CT in the intestine and serum was examined. Levels of CT-specific IgA antibodies and the numbers of cells producing these antibodies in the intestine were increased in mLN-resected rats. Particularly in the distal parts of the intestine, the jejunum and the ileum, IgA responses to orally administered antigens developed were stronger in the intestine after removal of the mLNs. This strongly indicates that the mLNs play a critical role in modulating the expansion of specific IgA responses. After removal of the mLNs, the lymph from the gut flows directly into the blood. It was investigated whether the spleen is involved in the initiation of an immune response to orally administered CT after removal of the mLNs. In the spleens of mLN-resected animals, proliferation was up-regulated, and germinal centres were formed in the follicles. However, CT-specific IgM(+) cells, but no IgA(+) cells, developed. Additionally, an increase of CT-specific IgM in the serum was found in mLN-resected animals. Thus, the data indicate that the spleen is involved in the immune response to CT after mLN resection.

SPECT-CT: a valuable method to document the regeneration of lymphatics and autotransplanted lymph node fragments

PURPOSE

The transplantation of lymph node fragments and stimulation of lymph vessel regeneration seems to be a promising model to prevent lymphoedema in patients after mammary tumour excision combined with axillary lymph node dissection and irradiation. This study evaluated the advantages of SPECT-CT in studying the regeneration of lymph vessels and lymphoid tissue after autologous lymph node transplantation.

METHODS

Five minipigs underwent autologous lymph node transplantation in the left groin. The lymph node was excised, cut into six pieces and embedded into two newly created subcutaneous pouches on this side. The superficial lymph node of the right groin was removed as a control. Five months after surgery the lymph flow of both legs was investigated using conventional lymphoscintigraphy and SPECT-CT with 10 MBq(99m)Tc-nanocolloid in combination with Berlin Blue injected subcutaneously into the draining area.

RESULTS

The integration of the transplanted lymph node fragments was shown. The SPECT-CT results correlated with the in situ findings observed at dissection. Afferent and efferent lymph flow could be followed up to the lumbar trunks. The use of SPECT-CT allowed exact localisation of the lymph node fragments in three-dimensional space and the regeneration of the lymph node fragments was documented histologically.

CONCLUSION

SPECT-CT is a good method to evaluate lymphatic flow and document lymph node regeneration. The data suggest that autologous lymph node transplantation is a promising model for prevention of lymphoedema.

Spleen plays an important role in the induction of accelerated blood clearance of PEGylated liposomes

It is well known that steric stabilization of the surface of liposomes by a polyethyleneglycol (PEG) conjugated lipid results in reduced recognition of the liposomes by the cells of the mononuclear phagocyte system and consequently extended circulation times of the liposomes (t1/2 approximately 20 h in rat). Recently, we reported on the "accelerated blood clearance (ABC) phenomenon", causing PEGylated liposomes to be cleared very rapidly from the circulation upon repeated injection. We also reported that abundant binding of IgM, secreted into the blood stream after the first dose and, to PEGylated liposomes, plays an essential role in the induction of the ABC phenomenon. Spleen is well known to play a central role in the immune reaction and to produce IgM following a bacterial infection. The aim of the present study was to determine whether spleen contributes to the induction of the ABC phenomenon and to unravel its role in the phenomenon. In rats that were splenectomized (surgical removal of spleen) prior to the first injection of liposomes (0.001 micromol phospholipids/kg), the ABC phenomenon was totally abolished. In these rats serum IgM concentrations as well as the amounts of IgM bound to PEGylated liposomes were substantially reduced. Splenectomy attenuated the ABC phenomenon when performed until 3 days post-first injection. Removal of the spleen 4 days post-first injection left the ABC phenomenon unchanged. This finding indicates that the immune reaction in the spleen against the PEGylated liposomes occurs during at least 2-3 days following the first administration and then IgM reactive to PEGylated liposomes is produced. The present study proves that the spleen plays a critical role in the induction phase of the ABC phenomenon. For effective clinical application, many liposomal drug formulations will require multiple injections. The ABC phenomenon described in this and several preceding papers therefore has important implications for the development and evaluation of therapeutically useful liposomal formulations requiring multiple-dose administration.

Resistência de ratos à peritonite fecal quando submetidos a esplenectomia e auto-implante do baço no retroperitônio

OBJETIVO: O estudo foi desenvolvido para avaliar os efeitos do autotransplante esplênico na proteção contra sepse abdominal em ratos Wistar jovens e adultos. MÉTODOS: Foram utilizados 54 ratos Wistar jovens e adultos (90 e 180 dias respectivamente) sendo distribuídos em 3 grupos: Grupo Sham, onde os animais eram submetidos a laparotomia com manipulação de alças apenas (n=6 animais jovens adultos), Grupo Esplenectomia, no qual os animais eram submetidos a esplenectomia total (n=10 animais jovens e adultos) e Grupo Auto-implante, onde os animais eram submetidos a esplenectomia total e um terço do baço era implantado em uma bolsa no retroperitônio (n=10 animais jovens e adultos). Após três meses os animais eram submetidos a nova laparotomia com ligadura e perfuração do ceco para estimular a sepse abdominal e acompanhados até o momento do óbito para estabelecimento de uma curva de mortalidade. RESULTADOS: Houve recuperação do baço implantado em todos os animais. Não houve diferença significativa entre o tempo de óbito entre os grupos. Os animais jovens aparentemente tiveram uma melhor resposta embora não estatisticamente significativa. CONCLUSÃO: Este estudo demonstrou que o auto-implante de baço no retroperitônio não provê proteção efetiva contra sepse abdominal em comparação aos ratos esplenectomizados.

Antibody Response of Autogenous Splenic Tissue Implanted in the Abdominal Cavity of Mice

There is still controversy about the immunologic function of autotransplanted splenic tissue. In this study, splenic autotransplantation was performed in the abdominal cavity of mice, and the plaque-forming cell (PFC) assay was used to investigate the frequency of antibody-forming cells in response to sheep red blood cell (SRBC) immunization. BALB/c mice were divided into four groups according to the location of the autogenous graft: intraomental (IO), free peritoneal splenosis (FPS), retroperitoneal (RP), and nongrafted control (CT). Thirty days after surgery the mice were immunized intraperitoneally with SRBCs, and 4 days later splenic immunoglobulin M anti-SRBC-secreting cells were determined by counting the number of PFCs. All the immunized mice showed increased numbers of PFCs that were about 2 logs higher than those in the the nonimmunized controls (P < 0.005). The frequencies of anti-SRBC-producing cells in the tissues grafted in various sites of the abdominal cavity (IO, FPS, RP), in the normal spleen from nonoperated controls (CT), or in the sham-operated control group (SCT) were not notably different (5582 +/- 2475 PFC/10(7) cells for IO; 4849 +/- 1856 for FPS; 6604 +/- 2903 for RP; 5940 +/- 5029 for CT; and 6172 +/- 2203 for SCT). Similar histology with small architectural variations was observed in all implants; less white pulp was involved, and there was more congestion in the red pulp, with extensive sinusoids and reticular fiber proliferation. This study shows that the T cell-dependent antibody response in implanted splenic tissues is as efficient as in the intact spleen, with no difference between the graft sites studied. This immune response does not depend on the slight architectural variations observed in the splenic implants.

Near-total splenectomy: a new technique for the management of hereditary spherocytosis

OBJECTIVE

The authors used a new surgical technique of near-total splenectomy (NTS) and report their experience.

SUMMARY BACKGROUND DATA

Total splenectomy is indicated for the management of patients with hereditary spherocytosis but may be complicated by severe infections and thromboembolic events. Studies have shown that partial or subtotal parenchymal resections can lead to excessive regeneration of the residual parenchyma. The resulting onset of hemolysis requires total splenectomy in a significant portion of patients. Our hypothesis was that a more radical approach to open resection permanently decreases recurrent hemolysis while potentially ensuring immune function.

METHODS

This longitudinal cohort study included 42 patients with moderate to severe hereditary spherocytosis who underwent NTS according to an open procedure developed by the authors. The end criterion was to conserve a remnant spleen of 10 cm in size.

RESULTS

Patient age ranged between 2 and 42 years. Mean resected spleen weight was 580 g; mean remnant volume was 10 cm (range, 8-11 cm). A surgical complication (loss of spleen) occurred in 1 patient. Six-month to 6-year follow-up data was available on 22 patients; 21 of 22 showed preserved phagocytosis and normal blood circulation of the remnant; 1 of 22 experienced secondary remnant necrosis. On average, the remnant spleen grew back to four and a half times its postoperative size. No patients required transfusions, developed gallstones, or symptomatic hemolysis.

CONCLUSIONS

This new technique of NTS is safe, effective, and can minimize the late sequelae of secondary splenectomy.

Regeneration of the spleen in intact animals and radiation chimeras

Regeneration of the splenic tissue after partial splenectomy is incomplete in adult non-irradiated mice and lethally irradiated animals reconstituted with donor syngeneic bone marrow. Transplantation of the splenic tissue to intact adult animals after partial splenectomy resulted in virtually complete regeneration of the spleen. In chimeras recovery of the splenic tissue was decreased; autotransplantation of the whole spleen or its part did not lead to appreciable changes in the weight and cellularity of this organ. No more than 30% splenic tissue is restored after complete splenectomy and transplantation of the splenic tissue in intact and chimeric mice.

Age-dependent development of the splenic marginal zone in human infants is associated with different causes of death

Infants are more susceptible to infections caused by T cell- independent type 2 (TI-2) polysaccharide antigens of certain encapsulated bacteria. Immune responses against this type of antigen are related to the splenic marginal zone (MZ). However, only few data exist on the age-dependent developmental stages of the human spleen in early childhood and on their association with different diseases. Therefore, the present study aimed to investigate spleens of a large number of children at very young ages (12 days to 32 months), derived from autopsy cases. Immunohistochemical labeling was performed on paraffin sections of 34 spleens using a panel of monoclonal antibodies. The shape and size of the white pulp compartments were examined and correlated to the cause of death of the children. Results show that the development of the different compartments was statistically age-dependent, but no clear-cut time point for the maturity of each compartment was seen. Furthermore, the MZ was significantly more often missing when sudden infant death (SID) and/or infection were the cause of death, compared with other violent or traumatic reasons that served as controls. This association supports the concept that an immature state of the spleen and especially of the MZ might contribute to the increased susceptibility to bacterial infections in young infants.

Lymphocyte function-associated antigen-1 and intercellular adhesion molecule-1 expression on B-cell subsets and the effects of splenectomy-experimental studies

There is an abundance of data dealing with recirculation of T cells in the rats, but relatively little is known about the traffic of B cells. The adhesion molecules expressed on the surface membrane are of great significance for recirculation of lymphocytes. However, very little is known about the expression of various adhesion molecules on B-cell subsets. Here we show that in normal rats various adhesion molecules are differentially expressed on B-cell subsets and that the level of their expression changes after the entry of B lymphocytes from the blood into the lymphoid tissues. In splenectomized rats, the surface expression of LFA-1 and ICAM-1 is selectively reduced on B-cell subsets in blood and lymph node, which is accompanied by a selective increase in the number of all B-cell subsets in the blood. The decreased surface expression of adhesion molecules results in faster migration of B lymphocytes through lymph nodes with subsequent accumulation of these cells in the blood.

Splenectomy of rats selectively reduces lymphocyte function-associated antigen 1 and intercellular adhesion molecule 1 expression on B-cell subsets in blood and lymph nodes

Splenectomy increases the number of B cells in the blood of humans and animals. It is unknown whether this is due to changes in migration, proliferation, or both. The numbers of naïve (IgD(+)IgM(+)), memory (IgD(-)IgM(high)), newly formed (IgM(high)CD90(high)), early recirculating follicular (IgM(low)CD90(high)), recirculating follicular (IgM(low)CD90(-)), and marginal zone (IgM(high)CD90(-)) phenotype B cells were determined in control and splenectomized rats by flow cytometry. All subsets increased significantly in the blood after splenectomy. Because surface molecules are involved in the regulation of migration and proliferation, their expression (lymphocyte function-associated antigen 1 [LFA-1], intercellular adhesion molecule 1 (ICAM-1), L-selectin, alpha4-integrins, CD44, major histocompatability complex class II, interleukin 2 receptor-alpha chain) was determined on B- and T-cell subsets of both groups. B cells, but not T cells, showed a significantly reduced LFA-1 and ICAM-1 expression in blood and lymph nodes, whereas the expression of the other surface molecules analyzed remained unchanged. The down-regulation of these molecules did not influence the adherence of B cells to high endothelial venules in vitro. In vivo, however, ICAM-1(low)-expressing B cells migrated significantly faster through lymph nodes (ICAM-1(low) 41 +/- 5 hours versus ICAM-1(high) 58 +/- 3 hours), whereas proliferation of B cells in bone marrow, lymph node, and blood remained unchanged. Thus, the presence of one organ is necessary for appropriate expression of LFA-1 and ICAM-1 on B cells in other, distant organs. The more rapid transit of ICAM-1(low) B cells through lymph nodes may be responsible for the increased B-cell number in the blood after splenectomy.

Spleen autotransplantation provides restoration of functional splenic lymphoid compartments and improves the humoral immune response to pneumococcal polysaccharide vaccine

After splenectomy, patients have an increased risk of overwhelming post-splenectomy infection (OPSI) or sepsis involving encapsulated bacteria such as pneumococcus. The value of spleen autotransplantation after splenectomy because of trauma has long been questioned. Much attention has been given to the restoration of mononuclear phagocyte system (MPS) function, which appeared to be similar to that of splenectomized individuals. The presence of specific anti-pneumococcal antibodies may enhance phagocytosis of opsonized bacteria by other parts of the MPS, as present in the liver. Therefore, in the present study we have evaluated the restoration of the humoral immune response after spleen autotransplantation, especially to pneumococcal capsular polysaccharides (PPS). Wistar rats were divided into three groups which were operated as follows: splenectomy, splenectomy followed by autotransplantation, and sham operation. After 12 weeks the rats were vaccinated with 23-valent pneumococcal vaccine. Blood samples were taken after 3 days, 3 and 6 weeks for anti-PPS IgM and IgG ELISA against types 3, 4, 6, 9, 14 and 23. In addition, immunohistological studies were performed on the autotransplants. Significant antibody titre rises were found in a main proportion of the autotransplanted rats, comparable to sham-operated rats. Splenectomized rats showed as well a significantly lower increase in immunoglobulin levels, as significant differences in the proportion of rats showing a minimum two-fold increase of antibody level, considered to represent an adequate response. The titres were highest 3 days after vaccination. Immunohistochemical studies demonstrated structurally functional autotransplants, including an intact marginal zone. Considering this significant anti- pneumococcal antibody response, spleen autotransplants can be expected to enable an improved humoral response to PPS, and to contribute to protection against OPSI after splenectomy.

Immune response capacity after human splenic autotransplantation: restoration of response to individual pneumococcal vaccine subtypes

OBJECTIVE

To evaluate features of general immune function, in particular the restoration of the humoral immune response to pneumococcal capsular polysaccharides, in humans undergoing a spleen autotransplantation after splenectomy because of trauma.

SUMMARY BACKGROUND DATA

After splenectomy, patients have an increased risk of overwhelming infection or sepsis involving encapsulated bacteria such as pneumococci. The value of human spleen autotransplantation after splenectomy because of trauma has long been questioned. Mononuclear phagocyte system function appeared to be similar to that in splenectomized persons. The presence of specific antipneumococcal antibodies would allow other parts of the mononuclear phagocyte system, such as those in the liver, to phagocytose opsonized bacteria.

METHODS

Ten consecutive patients undergoing splenectomy followed by autotransplantation were compared with the next 14 consecutive patients undergoing splenectomy alone. After a minimum of 6 months, the patients were vaccinated with 23-valent pneumococcal vaccine. Blood samples were taken at the time of vaccination and after 3 and 6 weeks for antipneumococcal capsular polysaccharides IgM and IgG enzyme-linked immunosorbent assay against types 3, 4, 6, 9, 14, and 23. Splenic regrowth was evaluated by scintigraphy.

RESULTS

Surprisingly, several of the nonautotransplanted patients showed scintigraphic activity, indicating the presence of either accessory spleens or traumatic seeding (splenosis). Significant antibody titer increases (more than twofold) were found for both IgM and IgG in the autotransplanted patients. Splenectomized-only patients showed no significant increase in Ig levels in patients without splenic regrowth and partial improvement in patients with splenosis/accessory spleens.

CONCLUSIONS

Considering this significant antipneumococcal antibody increase, spleen autotransplants can be expected to permit an adequate humoral response to pneumococcal infections and presumably also to other TI-2 antigens, and to protect against overwhelming postsplenectomy infection or sepsis.

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, PGP+ nerve fibers were revealed by immunohistology, and subdivided into nerve fibers of sympathetic (TH+, NPY+) or sensory (SP+, CGRP+) origin. In 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 initial innervation and the consequences of this innervation.

A non-expressed transgene as a cell marker for the investigation of cellular traffic after splenic autotransplantation

The investigation of cellular interactions during the regeneration of splenic transplants depends upon distinguishing host cells from graft derived cells. As a cell marker which, in contrast to many other marker systems, does not affect histocompatibility, the non-expressed transgene mMT-HGHRH-1 was introduced by mating into NMRI inbred mice to generate the transgenic mouse line BSM. By transplanting non-transgenic NMRI splenic tissue into transgenic BSM hosts, host derived cells could be identified in the transplants by in situ hybridization after regeneration. In a reciprocal approach, implant derived cells were detected in a transgenic transplant after 3 weeks of regeneration in a non-transgenic host. Relative amounts of transgenic cells in transplant cross-sections were estimated from the signal intensity of autoradiographs by densitometry and computer analysis. This approach could be broadly applied in studies of transplantation systems.

Both activated and nonactivated leukocytes from the periphery continuously enter the thymic medulla of adult rats: phenotypes, sources and magnitude of traffic

Although the thymus is primarily noted for the export of T cells to the periphery, a small influx of cells has also been observed. It is still a matter of debate whether entry into the thymus depends on prior activation. The phenotypes, sources and degree of immigration are largely unknown. We monitored by quantitative immunohistochemistry the entry of cells from the periphery into the rat thymus in three experimental models. We injected i.v. recirculating, small, nonactivated CD4+ T cell subsets, often referred to as naive (CD45RC+) and memory or antigen-experienced (CD45RC-) cells, purified from thoracic duct lymph of allotype-marked donors, allotype-marked leukocytes released from spleen or lung transplants, or leukocytes labeled in the periphery for 12 weeks during the S-phase of the cell cycle by oral application of 5-bromo-2-deoxyuridine (BrdUrd). Early after i.v. injection (0.5 h), significantly more antigen-experienced (CD45RC-) CD4+ T cells entered the thymus, and by 24 h four times as many cells from the CD45RC- subset as from the CD45RC+ subset had entered the thymus and localized to the medulla. None of the thymic entrants expressed the interleukin (IL)-2 receptor. Following spleen transplantation approximately 40% of donor cells entering the thymic medulla were T cells and approximately 55% were B cells. In contrast, from a lung transplant, approximately 85% of peripheral immigrants were T cells and approximately 10% were B cells. After both procedures, a small number of NK cells and monocytes/macrophages were found among the immigrants (< 5%). Rats were fed BrdUrd continuously for 12 weeks, a procedure which labeled approximately 30% of peripheral lymphocytes but not cortical thymocytes. BrdUrd-labeled cells were localized almost exclusively to the thymic medulla and represented approximately 10% of medullary cells. Of the thymic immigrants approximately 50% were T cells, approximately 30% were B cells (including approximately 15% IgD+ cells), approximately 15% were NK cells and the remainder (approximately 5%) were monocytes/macrophages. Only a quarter of BrdUrd-labeled cells expressed the IL-2 receptor. The thymus is continuously infiltrated by both activated and nonactivated leukocytes from the periphery, including T cells, B cells, NK cells and monocytes. These immigrants are supplied by lymphoid and nonlymphoid organs in a characteristic subset composition. Their entry is facilitated by prior antigen experience or activation. Thus, the participation of the thymic medulla in general leukocyte traffic suggests a mechanism by which the T cell repertoire could potentially be modulated by the peripheral tissues.

Lymphocyte traffic through lymph nodes and Peyer's patches of the rat: B- and T-cell-specific migration patterns within the tissue, and their dependence on splenic tissue

The migration routes of lymphocyte subsets through organ compartments are of importance when trying to understand the local events taking place during immune responses. We have therefore studied the traffic of B, T, CD4(+), and CD8(+ )lymphocytes through lymph nodes and Peyer s patches. At various time points after injection into the rat, labeled lymphocytes were localized, and their phenotype characterized in cryostat sections using immunohistochemistry. Morphometry was also performed, and the recovery of 51Cr-labeled lymphocytes in these organs was determined. B and T lymphocytes entered the lymph nodes via the high endothelial venules in similar numbers. Most B lymphocytes migrated via the paracortex (T cell area) into the cortex (B cell area), and then back in substantial numbers into the paracortex. In contrast, T lymphocytes predominantly migrated into the paracortex and were rarely seen in the cortex. No obvious differences were seen between various lymph nodes and Peyer s patches and the routes of CD4(+) and CD8(+)lymphocytes. After injection of lymphocytes into animals with autotransplanted splenic tissue, the number of B lymphocytes that had migrated into the B cell area of lymph nodes and of Peyer s patches was significantly decreased, whereas CD4(+) lymphocytes migrated in larger numbers into the T cell area of both organs.

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.

Development of the high endothelial venule in rat lymph node autografts

Vascular reconstruction during rat lymph node regeneration was investigated in autotransplanted mesenteric lymph node fragments, which had been implanted in the renal parenchyma. In addition to light microscopy, vascular casting and transmission electron microscopy were used. From day 3 onwards capillaries grew into the autografts together with lymphatic vessels. The capillaries showed obvious signs of proliferation by day 5. The surviving interstitial cells at the outer border of the transplant produced extracellular substance. High endothelial venules (HEV) differentiated from capillaries from about day 7. A first sign of their development was a vessel with a narrow, branching luminal space and with endothelial cells containing rich cytoplasm and small Golgi complexes. As the Golgi complexes grew and the cisternae and vesicles increased, the lumen dilated, the cell coat on the luminal surface became prominent, and, finally, lymphocytes emigrated through these venules from around day 10. The typical lymph node structure was complete by day 28. These results suggest that the interaction among the remaining interstitial cells, invading capillaries, and lymphatic penetration results in differentiation and maturation of HEV in lymph node regeneration. The development of Golgi complexes is strongly associated with lymphocyte emigration from the blood.

Autologous splenic transplantation for splenic trauma

OBJECTIVE

The authors reviewed the experimental evidence, surgical technique, complications, and results of clinical trials evaluating the role of autologous splenic transplantation for splenic trauma.

SUMMARY BACKGROUND DATA

Splenorrhaphy and nonoperative management of splenic injuries have now become routine aspects in the management of splenic trauma. Unfortunately, not all splenic injuries are readily amenable to conventional spleen-conserving approaches. Heterotopic splenic autotransplantation has been advocated for patients with severe grade IV and V injuries that would otherwise mandate splenectomy. For this subset of patients, splenic salvage by autotransplantation would theoretically preserve the critical role the spleen plays in the host's defense against infection.

METHODS

The relevant literature relating to experimental or clinical aspects of splenic autotransplantation was identified and reviewed. Data are presented on the experimental evaluation of autogenous splenic transplantation, methods and complications of autotransplantation, choice of anatomic site and autograft size, and results of clinical trials in humans.

RESULTS

The most commonly used technique of autotransplantation in humans involves implanting tissue homogenates or sections of splenic parenchyma into pouches created in the gastrocolic omentum. Most authors have observed evidence of splenic function with normalization of postsplenectomy thrombocytosis, immunoglobulin M levels, and peripheral blood smears. Some degree of immune function of transplanted grafts has been demonstrated with in vivo assays, but the full extent of immunoprotection provided by human splenic autotransplants is currently unknown.

CONCLUSIONS

Multiple human and animal studies have established that splenic autotransplantation is a relatively safe and easily performed procedure that results in the return of some hematologic and immunologic parameters to baseline levels. Some aspects of reticuloendothelial function are also preserved. Whether this translates into a real reduction in the morbidity or mortality rates from overwhelming bacterial infection is unknown and requires further investigation.

Splenic autotransplantation provides protection against fatal sepsis in young but not in old rats

Splenectomy increases the risk of contracting infections with high mortality. Thus, splenic tissue should be repaired orthotopically whenever possible. If all attempts fail, splenic autotransplantation might be a suitable method for splenic salvage. The protective function of such transplants in adults has been questioned, leading to a decreased frequency of splenic autotransplantations. However, the regeneration of splenic tissue is better in the young organism than in the old, suggesting that the protection provided by regenerated splenic tissue might be more reliable in children than in adults. In addition, children are at a higher risk in the case of overwhelming postsplenectomy sepsis. The protection warranted by regenerated splenic tissue after autotransplantation at different ages was examined using a highly standardized animal model. Sham operation, splenectomy, and splenic autotransplantation were performed on adult, weanling, and newborn rats, and Streptococcus pneumoniae was applied intranasally 9 months after the operation. After pneumococcal challenge about 80% of the splenectomized animals in the different age groups died of infection, whereas only 20% of the sham operated rats died. Regenerated splenic tissue resulting from splenic autotransplantation performed on adult or weanling rats demonstrated no protective function. However, in newborn rats with transplanted splenic tissue, both survival rate and survival time were increased significantly. Determination of lymphocyte subsets in the blood did not allow the protective role of splenic transplants to be predicted. This study indicates that disappointing results of splenic autotransplantation in adult patients should not lead to false pessimism about the role of this operation in children.

Regeneration of autotransplanted splenic tissue at different implantation sites

Inbred animals (Lewis rats) were used to investigate the regeneration of autologously implanted splenic tissue at intra-omental and subcutaneous sites. Quantitative immunohistology with monoclonal antibodies against lymphocytes and macrophages was performed to analyse the cell density of red pulp (RP), periarteriolar lymphoid sheath (PALS), marginal zone (MZ) and follicle, 7-180 days after transplantation. Antigenic, allogeneic and mitogenic stimulation and Northern blotting were also performed. Transplant groups differed from spleen only in the reduced size of PALS; however, quantitative analysis demonstrated subtle differences between spleen and transplants. The cell density of B-cells and ED-1+ macrophages was reduced in the RP, Tsupp/cyt-cells were decreased and B-cells increased in PALS, and B-cells and Thelper-cells reduced in the MZ. No differences could be detected between the transplant groups. Flow-cytometric analysis of cell suspensions from spleen and transplants revealed a reduction of T-cells (OX-19+), MHC-I and transferrin-receptor-bearing cells in both transplant groups, and a decrease in the number of Thelper-cells and ED-3+ macrophages in subcutaneous transplants. Both transplant groups were defective regarding the allogeneic and pokeweed mitogen response. Aberration of the lipopolysaccharide response was restricted to subcutaneous transplants, which additionally showed abnormal expression of interferon-gamma, interleukin-5 and interleukin-6 mRNA. Thus, subtle alterations of the newly developed microenvironment and/or lymphocyte-homing may influence the regeneration of splenic tissue; the implantation site may represent an important parameter in functional reorganisation.

Morphological analysis of neovascularization at early stages of rat splenic autografts in comparison with tumor angiogenesis

This study was undertaken to reveal the neovascularization at early stages of splenic autografts three-dimensionally, to illustrate the differences between it and tumor angiogenesis, and to establish its origin. Early vascular formation after transplantation of the rat spleen or Walker tumor into the major omentum was examined by using a video macroscope, vascular casting methods and the organ culture technique. A complex vascular network layer (vascular cortex) was first formed beneath the capsule of an autograft; later, vascular buds grew from this network toward the necrotic center. They anastomosed and changed into a form resembling withered twigs (vascular medulla). Tumor angiogenesis did not present such morphological features and was characterized by capillary loop formation with a columnar vertex resembling an "inverted V". This fundamental structure did not change throughout angiogenesis except for dilation and irregularity of vascular diameter. The organ culture technique demonstrated that the preliminary vasculature was formed in splenic autografts by regeneration of preexisting vessels in the graft and not by invading capillaries. Transmission electron microscopy showed that the cells present had characteristics of sinus endothelial cells. These results suggest that preexisting sinus endothelial cells rearrange themselves after devascularization and reconstruct a new vasculature that anastomoses with the penetrating capillaries. This mechanism establishes vascular circulation at an early stage, and accelerates regeneration of the splenic autograft before complete necrosis.