Lymphocyte subsets in the blood. The influence of splenectomy, splenic autotransplantation, ageing, and the site of blood sampling on the number of B, T, CD4+, and CD8+ lymphocytes in the rat

Participation of the spleen in the neuroinflammation after pilocarpine-induced status epilepticus: implications for epileptogenesis and epilepsy

Epilepsy, a chronic neurological disorder characterized by recurrent seizures, affects millions of individuals worldwide. Despite extensive research, the underlying mechanisms leading to epileptogenesis, the process by which a normal brain develops epilepsy, remain elusive. We, here, explored the immune system and spleen responses triggered by pilocarpine-induced status epilepticus (SE) focusing on their role in the epileptogenesis that follows SE. Initial examination of spleen histopathology revealed transient disorganization of white pulp, in animals subjected to SE. This disorganization, attributed to immune activation, peaked at 1-day post-SE (1DPSE) but returned to control levels at 3DPSE. Alterations in peripheral blood lymphocyte populations, demonstrated a decrease following SE, accompanied by a reduction in CD3+ T-lymphocytes. Further investigations uncovered an increased abundance of T-lymphocytes in the piriform cortex and choroid plexus at 3DPSE, suggesting a specific mobilization toward the Central Nervous System. Notably, splenectomy mitigated brain reactive astrogliosis, neuroinflammation, and macrophage infiltration post-SE, particularly in the hippocampus and piriform cortex. Additionally, splenectomized animals exhibited reduced lymphatic follicle size in the deep cervical lymph nodes. Most significantly, splenectomy correlated with improved neuronal survival, substantiated by decreased neuronal loss and reduced degenerating neurons in the piriform cortex and hippocampal CA2-3 post-SE. Overall, these findings underscore the pivotal role of the spleen in orchestrating immune responses and neuroinflammation following pilocarpine-induced SE, implicating the peripheral immune system as a potential therapeutic target for mitigating neuronal degeneration in epilepsy.

Adenosine 2A receptor antagonists promote lymphocyte proliferation in sepsis by inhibiting Treg expression of PD-L1 in spleen

The spleen is essential for lymphocyte proliferation, which is associated to sepsis prognosis. Adenosine 2A receptor (A2AR) blocking promotes lymphocyte proliferation in sepsis, however the mechanism is uncertain. Our sepsis cecum ligation perforation model showed that blocking A2AR increased survival and CD4+ cell numbers in a spleen-dependent mechanism. The sequencing of the transcriptome of the spleen indicated alterations in the expression of genes involved in the control of lymphocyte proliferation by inhibiting A2AR, including a reduction in the expression of PD-L1. Flow cytometry analysis of PD-L1 expression intensity in splenic cell subpopulations revealed that the Treg cell subpopulation was the strongest PD-L1-expressing cell population, and Treg PD-L1 expression decreased after blocking A2AR. In vitro activation of A2AR was able to upregulate PD-L1 expression of Treg and boost Treg capacity to limit lymphocyte proliferation, while blockage of PD-L1 partly reduced A2AR-activated Treg's ability to inhibit lymphocyte proliferation. In addition, blocking CREB phosphorylation significantly inhibited A2AR-induced PD-L1 expression. According to the findings of our research, inhibiting A2AR improves the prognosis of sepsis by lowering the level of PD-L1 expression by Treg in the spleen and reducing the inhibition of lymphocyte proliferation.

Predicted limited redistribution of T cells to secondary lymphoid tissue correlates with increased risk of haematological malignancies in asplenic patients

The spleen, a secondary lymphoid tissue (SLT), has an important role in generation of adaptive immune responses. Although splenectomy remains a common procedure, recent studies reported poor prognosis and increased risk of haematological malignancies in asplenic patients. The high baseline trafficking of T lymphocytes to splenic tissue suggests splenectomy may lead to loss of blood-borne malignant immunosurveillance that is not compensated for by the remaining SLT. To date, no quantitative analysis of the impact of splenectomy on the human T cell trafficking dynamics and tissue localisation has been reported. We developed a quantitative computational model that describes organ distribution and trafficking of human lymphocytes to explore the likely impact of splenectomy on immune cell distributions. In silico splenectomy resulted in an average reduction of T cell numbers in SLT by 35% (95%CI 0.12–0.97) and a comparatively lower, 9% (95%CI 0.17–1.43), mean decrease of T cell concentration in SLT. These results suggest that the surveillance capacity of the remaining SLT insufficiently compensates for the absence of the spleen. This may, in part, explain haematological malignancy risk in asplenic patients and raises the question of whether splenectomy has a clinically meaningful impact on patient responses to immunotherapy.

Effects of disease-modifying therapy on peripheral leukocytes in patients with multiple sclerosis

Modern disease-modifying therapies (DMTs) in multiple sclerosis (MS) have variable modes of action and selectively suppress or modulate the immune system. In this review, we summarize the predicted and intended as well as unwanted adverse effects on leukocytes in peripheral blood as a result of treatment with DMTs for MS. We link changes in laboratory tests to the possible therapeutic risks that include secondary autoimmunity, infections, and impaired response to vaccinations. Profound knowledge of the intended effects on leukocyte counts, in particular lymphocytes, explained by the mode of action, and adverse effects which may require additional laboratory and clinical vigilance or even drug discontinuation, is needed when prescribing DMTs to treat patients with MS.

Effect of non-operative management (NOM) of splenic rupture versus splenectomy on the distribution of peripheral blood lymphocyte populations and cytokine production by T cells

Post-traumatic splenectomy is associated with increased postoperative morbidity and mortality and long-term impairment of humoral and cellular immunity. Alternatives to surgery have been developed to minimize or avoid the immediate and/or long-term complications of splenectomy. Herein we investigated the long-term effect of non-operative management (NOM) of the traumatic rupture of the spleen on the distribution of peripheral blood (PB) lymphocyte populations and cytokine production by T cells. PB samples were drawn from six NOM patients, 13 age-matched adults who had undergone splenectomy after trauma (SP patients) and 31 age-matched controls. Cellular phenotypes and the intracellular production of interferon (IFN)-gamma, interleukin (IL)-2, IL-4 and IL-10 cytokines in T cells were determined in whole blood +/- mitogens by flow cytometry. NOM patients did not show any changes in the absolute numbers of lymphocytes or the distribution of their subsets, compared to the controls. In contrast, SP patients showed a sustained increase in the percentage and/or absolute numbers of lymphocytes, CD8 T cells, activated CD8 T cells, natural killer (NK) T cells, NK cells and gammadelta T cells, and a reduction in naive CD4 T cells. The constitutive or induced cytokine production by T cells of the NOM group was similar to the control group, whereas SP patients had increased percentages of constitutive IL-2- and IFN-gamma-producing CD8 T cells and IFN-gamma-producing CD4 T cells. Our findings indicate collectively that the healing process in NOM does not affect the architecture of the spleen to such an extent that it would lead to long-term alterations of the proportions of PB lymphocytes or the T cell cytokine profiles.

Influência do baço, da asplenia e do implante esplênico autógeno no metabolismo lipídico de camundongos

OBJETIVO: Estudar a influência do baço, da asplenia e do implante esplênico autógeno no metabolismo lipídico, por meio da avaliação do lipidograma sérico de camundongos e da verificação do efeito do transplante autógeno de baço em diferentes locais do abdome. MÉTODO: Foram utilizados camundongos BALB/c distribuídos em sete grupos de 10 animais: controle normal (CN); controle obeso (CO); operação simulada (OS); esplenectomia total (ET); três grupos submetidos ao transplante autógeno do baço: omento maior (OM), retroperitônio (RP), tecido subcutâneo da parede abdominal (PA). Os animais, com exceção do grupo CN, foram submetidos a dieta com 1,25% de colesterol. A intervenção cirúrgica foi realizada 30 dias após o início da dieta. A coleta de sangue ocorreu no 60º dia pós-operatório. Foram dosados os níveis de triglicérides, de colesterol total e de suas frações, bem como a glicemia. O baço, os implantes esplênicos e o fígado foram submetidos a estudo histológico. RESULTADOS: A dieta aumentou os níveis plasmáticos de colesterol total, HDL e LDL dos camundongos (p < 0,05 versus CN). Entre os animais em uso da dieta, não houve diferença no lipidograma dos grupos controles (CO e OS) quando comparados ao grupo esplenectomizado (ET), assim como em relação aos animais submetidos ao transplante autógeno do baço (OM, RP, PA). A capacidade de preservação da arquitetura histológica esplênica foi semelhante nos três locais de implante. Todos os animais que utilizaram a dieta enriquecida apresentaram esteatose hepática. CONCLUSÃO: De acordo com os resultados obtidos o baço não parece participar da regulação dos níveis de lipídeos plasmáticos em camundongos BALB/c.

Lymphocyte numbers and subsets in the human blood. Do they mirror the situation in all organs?

Lymphocyte numbers in the blood are used to evaluate the immune status on a daily basis in medicine. Several studies have documented the normal ranges of lymphocytes and lymphocyte subsets in the peripheral blood. A variety of techniques and criteria have revealed clear differences between the lymphocyte subsets in childhood and adolescence. Race and gender are also variables for blood lymphocytes, and even environmental factors seem to influence the numbers of some lymphocyte populations. However, do all these variations in lymphocyte subsets in the peripheral blood mirror changes in the lymphocyte populations of the whole body, or is it just a result of different migratory habits of cells? The factors influencing the distribution of lymphocytes in the peripheral blood with regard to the different abilities of T and B cells to migrate to distinct lymphoid or non-lymphoid tissue are summarized. In addition it will be described how the removal of organs (e.g. thymus, spleen, liver) influences the distribution of lymphocytes in the blood. All these parameters should be considered not only in the clinical situation when the immune status of a patient is extrapolated from the lymphocyte numbers in the blood, but also when interpreting treatment effects in patients.

Lymphocyte migration into different lung compartments during an antigen induced inflammation: is the spleen a major reservoir of these lymphocytes?

The hypothesis was tested whether lymphocytes of immunized and pulmonary challenged LEW rats adhere in higher numbers to the lung vascular bed than control lymphocytes and whether these immigrating cells come from the spleen. The kinetic of a primary immune response to sheep red blood cells (SRBC) was characterized in different lung compartments such as the vascular marginal pool, the interstitium and the bronchoalveolar space. The adherence of genetically labeled splenocytes from SRBC-immunized and challenged rats and from non-challenged rats was investigated in challenged lungs using the ex vivo system of the isolated buffer-perfused lung (IPL). Furthermore, immunized animals were splenectomized and challenged with SRBC. It was found that lymphocytes were increased with a maximum in the lung interstitium on day 3 and in the bronchoalveolar lavage fluid (BALF) on day 4. The adhesion to the pulmonary vascular endothelium of splenic T cells from SRBC-immunized rats in the IPL was not significantly increased compared to those from control animals. A significant transmigration from the vasculature into the BALF was not found. On day 4 after challenge the cell numbers in the lung compartments of the splenectomized animals were comparable to controls. The spleen alone has no significant role as a source of lymphocytes in lung inflammation. Therefore, the pulmonary immune response seems to be triggered mainly by the local environment and not by the accompanying systemic immune reaction.

In Vitro Study of the Long-Term Effects of Post-Traumatic Splenectomy on Cellular Immunity

The purpose of this study was to investigate the effect of splenectomy on cellular immunity. We studied the cellular phenotype and type 1 [interferon-gamma, interleukin-2 (IL-2)] and type 2 (IL-4 and IL-10) cytokine-producing peripheral blood CD4+ and CD8+ T lymphocytes in 22 healthy adults who had undergone post-traumatic splenectomy about 1 to 35 years ago. Splenectomy resulted in a long-term reduction of the percentage of CD4+CD45RA+ cells and a late increase of the percentage and absolute numbers of T-cell receptor gamma/delta cells. Stimulation with Staphylococcal enterotoxin B resulted in normal IL-2 production by CD4+ T cells, indicating that the naïve cells were not anergic. Splenectomy also resulted in long-term priming of both CD4+ and CD8+ T cells. During the first 8 years, both type 1 and type 2 CD4+ T cells were primed to varying degrees. About 8 years later, the percentage of primed type 2 CD4+ T cells subsided, but that of type 1 CD4+ T cells, although decreased, remained detectable over a longer period. Priming of CD8+ T cells persisted throughout the study period. The long-term priming of type 1 CD4+ and CD8+ T cells, which may result in partial impairment of T-cell functions, may explain reported defects of immune responses to recall antigens in splenectomized individuals. In addition, changes in the profile of primed CD4+ T cells with time may be clinically relevant to relapses in autoimmune thrombocytopenia after splenectomy.

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.

Social rearing conditions before weaning influence numbers and proportions of blood immune cells in laboratory rats

The influence of the early social rearing environment on blood cellular immunity was investigated in the male offspring of Long-Evans rats. Sons of females housed in pair groups (P-males) and sons of females living in a mixed sex colony (C-males) were studied. After weaning at the age of 21 days, offspring were housed individually to ensure identical experiences until the age of 100 days when immunological assessments were conducted. C-males had significantly higher numbers of blood CD4 and CD8 T cells as well as higher numbers of granulocytes and monocytes than P-males. In contrast, the number of B cells and NK cells was similar in P- and C-males. T-cell responsiveness to ConA, determined in the peripheral blood mononuclear cells and whole blood assays, did not differ significantly between the two groups. The study indicates that the early social environment affects numbers and proportions of many blood immune cell subsets in later life.

Long-term colony housing in Long Evans rats: immunological, hormonal, and behavioral consequences

The distribution pattern and the function of blood immune cells were investigated for 10 weeks in three mixed-sex colonies of Long Evans rats. After colony formation, a despotic dominance system was established between the males. This paper focuses on differences between subdominant colony and pair-housed control males. A reduced body mass development and hormonal status in subdominant males indicate stressful colony conditions. Subdominant males had lower numbers of CD4 and CD8 T cells, pronounced granulocytosis and reduced lymphocyte proliferation rates as compared with controls. The persistency of changes in subdominant males offers the opportunity to investigate the effects of long-term immuno-modulation on health.

Splenectomy selectively affects the distribution and mobility of the recirculating lymphocyte pool

The spleen plays a major role in immune surveillance, but the impact that splenectomy exerts on the immune competence of an individual is not fully resolved. Here we show that neonatal splenectomy in sheep does not abrogate the development of a large, nonrecirculating pool of lymphocytes and that it has no effect on the acquisition of a normal blood lymphocyte profile. Splenectomy did, however, result in a significant decrease in blood residency time of recirculating lymphocytes and in an enhanced accumulation of recirculating lymphocytes in lymph nodes. Furthermore, nonrecirculating peripheral blood lymphocytes were less likely to migrate to the lung, possibly because of saturation of the marginal pool by recirculating lymphocytes. Although splenectomy has little effect on the development or distribution of lymphocyte subsets in blood and lymph, it has marked effects on the rate of recirculation of lymphocytes, which may have significant implications for peripheral immune surveillance in patients who undergo splenectomy.

Splenectomy selectively affects the distribution and mobility of the recirculating lymphocyte pool

The spleen plays a major role in immune surveillance, but the impact that splenectomy exerts on the immune competence of an individual is not fully resolved. Here we show that neonatal splenectomy in sheep does not abrogate the development of a large, nonrecirculating pool of lymphocytes and that it has no effect on the acquisition of a normal blood lymphocyte profile. Splenectomy did, however, result in a significant decrease in blood residency time of recirculating lymphocytes and in an enhanced accumulation of recirculating lymphocytes in lymph nodes. Furthermore, nonrecirculating peripheral blood lymphocytes were less likely to migrate to the lung, possibly because of saturation of the marginal pool by recirculating lymphocytes. Although splenectomy has little effect on the development or distribution of lymphocyte subsets in blood and lymph, it has marked effects on the rate of recirculation of lymphocytes, which may have significant implications for peripheral immune surveillance in patients who undergo splenectomy.

Long-term decrease of CD4+CD45RA+ T cells and impaired primary immune response after post-traumatic splenectomy

Congenital or acquired absence of the spleen and functional hyposplenism are associated with abnormalities of host defence such as an increased susceptibility to infection with encapsulated bacteria. The effects of the lack of the spleen on cell-mediated immunity are largely unknown. In the present study we have investigated peripheral blood lymphocyte subpopulations in healthy adults who had undergone splenectomy because of severe abdominal trauma > 4 years before the study. The results show a significant reduction in the percentage of CD4+ T cells due to a selective and long-term decrease in the percentage of CD4+CD45RA+ lymphocytes, the CD4+ T-cell subset mainly involved in primary immune responses to newly encountered antigens. Levels of the reciprocal CD45RO+CD4+ T-cell subset were comparable between splenectomized and control individuals, as were lymphoproliferative responses and IFN-gamma production to recall antigens. Decreased levels of CD4+CD45RA+ cells were accompanied by an impairment in primary immune responsiveness, as assessed by investigating T-cell proliferation to stimulation with keyhole limpet haemocyanin and by measuring antibody responses following primary immunization with a clinically relevant T-dependent antigen, hepatitis A vaccine, in vivo. These findings suggest a possible role of the spleen in the generation, maintenance and/or differentiation of naive, unprimed T cells or their precursors, which might have a possible functional relevance for primary immune responses following splenectomy.

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.

Distinct Recirculating and Non-Recirculating B-Lymphocyte Pools in the Peripheral Blood Are Defined by Coordinated Expression of CD21 and L-Selectin

The continual recirculation of lymphocytes between the blood, tissues, and lymph is essential for the coordination and dissemination of immune responses. We have compared the functional and phenotypic properties of lymphocytes isolated from blood and lymph, the two major migratory populations. Lymph-borne lymphocytes migrated readily into the lymphatic recirculation pathway, but greater than one third of all peripheral blood lymphocytes (PBLs) were excluded from the lymphatic circuit and showed an enhanced migration to the spleen. Phenotypic analysis showed that most non-recirculating PBLs were B cells. The migration competence of B cells correlated with the surface expression of CD21 and L-selectin; recirculating B cells expressed both of these molecules, whereas non-recirculating B cells lacked both antigens. These results establish that blood contains distinct pools of lymphocytes that differ in their recirculation competence. Clearly, blood sampling is not an efficient method to directly measure the status of the recirculating immune system, and implies important constraints and restrictions in the interpretation of experimental or clinical data that include phenotypic and quantitative analyses of blood lymphocytes.

Distinct Recirculating and Non-Recirculating B-Lymphocyte Pools in the Peripheral Blood Are Defined by Coordinated Expression of CD21 and L-Selectin

The continual recirculation of lymphocytes between the blood, tissues, and lymph is essential for the coordination and dissemination of immune responses. We have compared the functional and phenotypic properties of lymphocytes isolated from blood and lymph, the two major migratory populations. Lymph-borne lymphocytes migrated readily into the lymphatic recirculation pathway, but greater than one third of all peripheral blood lymphocytes (PBLs) were excluded from the lymphatic circuit and showed an enhanced migration to the spleen. Phenotypic analysis showed that most non-recirculating PBLs were B cells. The migration competence of B cells correlated with the surface expression of CD21 and L-selectin; recirculating B cells expressed both of these molecules, whereas non-recirculating B cells lacked both antigens. These results establish that blood contains distinct pools of lymphocytes that differ in their recirculation competence. Clearly, blood sampling is not an efficient method to directly measure the status of the recirculating immune system, and implies important constraints and restrictions in the interpretation of experimental or clinical data that include phenotypic and quantitative analyses of blood lymphocytes.

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.

Risk of cancer following splenectomy

Only 2 small population-based studies have previously evaluated cancer risk in splenectomized patients. Our objective was thus to investigate cancer incidence following splenectomy for external trauma or for surgical treatment of non-malignant conditions of adjacent organs. Using the unique personal identification number assigned to each Swedish resident, we linked centralized hospitalization records with nationwide total population and cancer incidence data. We excluded cancers diagnosed within the first 12 months after splenectomy and computed standardized incidence ratios for 1,295 patients (contributing 14,390 person-years) splenectormized for external trauma and for 985 patients (contributing 8,91 1 person-years) whose splenectomy accompanied surgical treatment of non-malignant conditions of adjacent organs (mostly peptic ulcers), using age-, sex- and period-specific rates for cancer incidence derived from the entire Swedish population. Patients undergoing splenectomy for external trauma had no significant excess of total or site-specific cancers. Individuals splenectormized in conjunction with surgery for non-malignant conditions of adjacent organs had a non-significant 40% elevated risk of total cancer, with significant increases of lung and ovarian cancers. The excesses of lung and ovarian cancers may be due to chance, but we could not exclude the conditions for which the surgery was performed, other treatments or common predisposing factors (such as cigarette smoking, which has been linked with both peptic ulcer and lung cancer).

Natural immunity and chronic exercise in rats. The involvement of the spleen and the splenic nerves

We have previously shown that voluntary running for 4-5 weeks in the spontaneously hypertensive rat (SHR) significantly increased in natural cytotoxic mechanism in vivo, measured as clearance of 51Cr YAC-1 lymphoma cells from the lungs. In the present study, we have studied the possible role of the spleen and the splenic nerves in this augmentation. The SHR were randomly allocated to either a voluntary exercise group or a sedentary control group. After four weeks of exercise the runners and sedentary control SHR were further assigned to one of four groups: 1) no surgery, 2) sham operation, 3) splenic nerve section and 4) splenectomy. Splenectomy drastically reduced in vivo cytotoxicity in both runners and sedentary controls, but in vivo cytotoxicity of splenectomized voluntary runners was significantly higher than that of splenectomized sedentary control animals. Selective denervation of the spleen did not affect the in vivo cytotoxicity. These results indicate that the enhanced in vivo natural cytotoxic mechanism following voluntary chronic exercise in SHR is partly dependent on intact splenic function. However, this enhancement does not seem to be mediated by the splenic sympathetic nerves.

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.

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.

The effect of fenclofenac on the regeneration of lymphocytes in rats following total body irradiation

The effect of fenclofenac on the regeneration of white blood cells in Sprague-Dawley rats following total body irradiation was investigated. The lowest dose of total body irradiation that would suppress the peripheral blood lymphocyte count by at least 50% was found to be 1.0 Gray in a preliminary experiment. Fenclofenac in a dose of 150 mg/kg/day retarded the regeneration of lymphocytes following total body irradiation of 1 Gray: this effect was also seen in the CD4, CD8 and B-lymphocyte subsets. This suppressive effect in vivo may be due to interference with replicative growth of white blood cells since previous in vitro experiments have shown suppression of lymphocyte growth at a stage later than activation in the cell cycle. The suppressive effects on leucocyte regeneration in vivo suggest that fenclofenac may have promise as an immunosuppressive drug with fewer serious side effects than the currently available immunosuppressive drugs.

Blood B, T, CD4+ and CD8+ lymphocytes in female Wistar rats

We have established reference values of peripheral blood lymphocyte subsets in healthy female Wistar rats under highly standardized conditions. Using monoclonal antibodies and flow cytometry, T lymphocytes (OX19+), B lymphocytes (OX6+ and anti-Ig+), T-helper/inducer (W3/25+), and T-suppressor/cytotoxic subsets (OX8+) were determined, from week 11 to week 21 after birth. The mean percentages of T and B lymphocytes with respect to total lymphocytes were 78.5% and 18%, respectively; the mean percentages of T-helper/inducer and T-suppressor/cytotoxic cells in relation to T lymphocytes were 59% and 25%, respectively (n = 48). No difference in total leukocyte count, differential leukocyte analysis, or lymphocyte subsets was observed during the 10 weeks the rats were studied under standard housing conditions. Therefore, the period considered seems the most appropriate in which to carry out experiments that could involve lymphocyte subset disturbances.

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.

Lymphocyte subsets in the blood: a diagnostic window on the lymphoid system?

The assessment of peripheral blood lymphocyte numbers and ratios has been performed in almost every conceivable disease state, but do these values give any useful information about immune status? Jürgen Westermann and Reinhard Pabst try to answer this question and to put peripheral blood population assessments into the whole-body context.