Immunohistology of the human spleen: an inventory of the localization of lymphocyte subpopulations

Anatomical structures, cell types and biomarkers of the Human Reference Atlas

The Human Reference Atlas (HRA) aims to map all of the cells of the human body to advance biomedical research and clinical practice. This Perspective presents collaborative work by members of 16 international consortia on two essential and interlinked parts of the HRA: (1) three-dimensional representations of anatomy that are linked to (2) tables that name and interlink major anatomical structures, cell types, plus biomarkers (ASCT+B). We discuss four examples that demonstrate the practical utility of the HRA.

Post-splenectomy sepsis: preventative strategies, challenges, and solutions

Removal of the spleen had already been established as a routine technique to treat splenic trauma and other diseases affecting the spleen before the anatomy, physiology, and function of the spleen were known in the mid-twentieth century. It is now widely accepted that the splenectomized individual is at increased risk for infection, in particular, overwhelming post-splenectomy infection (OPSI). OPSI is a syndrome of fulminant sepsis occurring in splenectomized (asplenic) or hyposplenic individuals that is associated with high mortality and morbidity. Poorly opsonized bacteria such as encapsulated bacteria, in particular, Streptococcus pneumoniae, are often implicated in sepsis. The spleen is a reticuloendothelial organ that facilitates opsonization and phagocytosis of pathogens, in addition to cellular maintenance. Splenectomy is associated with an impairment in immunoglobulin production, antibody-mediated clearance, and phagocytosis, leading to an increased risk of infection and sepsis. Early identification of the at-risk patient, early blood cultures prior to antibiotic administration, urgent blood smears and fast pathogen-detection tests, and sepsis bundles should be utilized in these patients. Prompt management and aggressive treatment can alter the course of disease in the at-risk splenectomized patient. Overwhelming post-splenectomy infection can be prevented through vaccination, chemoprophylaxis, and patient education. This article evaluates post-splenectomy sepsis by summarizing the anatomy and function of the spleen, physiological changes after splenectomy that predispose the splenectomized patient to infection, and current management and prevention strategies.

Anatomy, immunohistochemistry, and numerical distribution of human splenic microvessels

The microvascular architecture of the spleen plays an important role in the immunological function of this organ. The different types of vessels are related to different reticular cells each with their own immunomodulatory functions. The present study describes an immunohistochemical and morphometric analysis of the various types of vessels in 21 human autopsy non-pathological splenic samples. On an area of 785,656.37 μm² for each sample, we classified and quantified the type and number of vascular structures, each according to their morphology and immunohistochemical profile, and obtained the ratios between them. The distribution of trabecular vessels and the characteristics of the venules are reviewed. In our material the so-called "cavernous perimarginal sinus" (anatomical structure previously described by Schmidt et al., 1988) was observed and interpreted as a curvilinear venule shaped by the follicle in contact with the trabecular vein. Our material comprised 261 trabeculae (containing 269 arterial sections and 508 venous sections), 30,621 CD34+ capillaries, 7739 CD271+ sheathed capillaries, 2588 CD169+ sheathed capillaries, and 31,124 CD8+ sinusoids. The total area (TA) (14,765,714.88 μm²) occupied by the sinusoidal sections of the 21 cases was much higher than the TA of the capillary sections (1,700,269.83 μm²). Similarly, the TA (651,985 μm²) occupied by the sections of the trabecular veins was much higher than the TA of the trabecular arteries (88,594 μm²). The total number of CD34+ capillaries and of sinusoids CD8+ was similar for the sum of the 21 cases, nevertheless there were large differences in each case. Statistically the hypothesis that the number of capillaries and sinusoids are present with the same frequency is discarded. In view of the absence of a numerical correlation between capillaries and sinusoids, we postulate that very possibly the arterial and the venous vascular trees are two anatomically independent structures separated by the splenic cords. We believe that this is the first work where splenic microvascularization is simultaneously approached from a morphometric and immunohistochemical point of view.

Langerin+CD8+ Dendritic Cells in the Splenic Marginal Zone: Not So Marginal After All

Dendritic cells (DC) fulfill an essential sentinel function within the immune system, acting at the interface of innate and adaptive immunity. The DC family, both in mouse and man, shows high functional heterogeneity in order to orchestrate immune responses toward the immense variety of pathogens and other immunological threats. In this review, we focus on the Langerin⁺CD8⁺ DC subpopulation in the spleen. Langerin⁺CD8⁺ DC exhibit a high ability to take up apoptotic/dying cells, and therefore they are essential to prime and shape CD8⁺ T cell responses. Next to the induction of immunity toward blood-borne pathogens, i.e., viruses, these DC are important for the regulation of tolerance toward cell-associated self-antigens. The ontogeny and differentiation pathways of CD8⁺CD103⁺ DC should be further explored to better understand the immunological role of these cells as a prerequisite of their therapeutic application.

Emerging Role of the Spleen in the Pharmacokinetics of Monoclonal Antibodies, Nanoparticles and Exosomes

After being absorbed, drugs distribute in the body in part to reach target tissues, in part to be disposed in tissues where they do not exert clinically-relevant effects. Therapeutically-relevant effects are usually terminated by drug metabolism and/or elimination. The role that has been traditionally ascribed to the spleen in these fundamental pharmacokinetic processes was definitely marginal. However, due to its high blood flow and to the characteristics of its microcirculation, this organ would be expected to be significantly exposed to large, new generation drugs that can hardly penetrate in other tissues with tight endothelial barriers. In the present review, we examine the involvement of the spleen in the disposition of monoclonal antibodies, nanoparticles and exosomes and the possible implications for their therapeutic efficacy and toxicity. The data that we will review lead to the conclusion that a new role is emerging for the spleen in the pharmacokinetics of new generation drugs, hence suggesting that this small, neglected organ will certainly deserve stronger attention by pharmacologists in the future.

Human spleen microanatomy: why mice do not suffice

The microanatomical structure of the spleen has been primarily described in mice and rats. This leads to terminological problems with respect to humans and their species-specific splenic microstructure. In mice, rats and humans the spleen consists of the white pulp embedded in the red pulp. In the white pulp, T and B lymphocytes form accumulations, the periarteriolar lymphatic sheaths and the follicles, located around intermediate-sized arterial vessels, the central arteries. The red pulp is a reticular connective tissue containing all types of blood cells. The spleen of mice and rats exhibits an additional well-delineated B-cell compartment, the marginal zone, between white and red pulp. This area is, however, absent in human spleen. Human splenic secondary follicles comprise three zones: a germinal centre, a mantle zone and a superficial zone. In humans, arterioles and sheathed capillaries in the red pulp are surrounded by lymphocytes, especially by B cells. Human sheathed capillaries are related to the splenic ellipsoids of most other vertebrates. Such vessels are lacking in rats or mice, which form an evolutionary exception. Capillary sheaths are composed of endothelial cells, pericytes, special stromal sheath cells, macrophages and B lymphocytes. Human spleens most probably host a totally open circulation system, as connections from capillaries to sinuses were not found in the red pulp. Three stromal cell types of different phenotype and location occur in the human white pulp. Splenic white and red pulp structure is reviewed in rats, mice and humans to encourage further investigations on lymphocyte recirculation through the spleen.

Differences in Anti-Inflammatory Actions of Intravenous Immunoglobulin between Mice and Men: More than Meets the Eye

Intravenous immunoglobulin (IVIg) is a therapeutic preparation of polyspecific human IgGs purified from plasma pooled from thousands of individuals. When administered at a high dose, IVIg inhibits inflammation and has proven efficacy in the treatment of various autoimmune and systemic inflammatory diseases. Importantly, IVIg therapy can ameliorate both auto-antibody-mediated and T-cell mediated immune pathologies. In the last few decades, extensive research in murine disease models has resulted in the elucidation of two novel anti-inflammatory mechanisms-of-action of IVIg: induction of FcγRIIB expression by sialylated Fc, and stimulation of regulatory T cells. Whereas controversial findings in mice studies have recently inspired intense scientific debate regarding the validity of the sialylated Fc-FcγRIIB model, the most fundamental question is whether these anti-inflammatory mechanisms of IVIg are operational in humans treated with IVIg. In this review, we examine the evidence for the involvement of these anti-inflammatory mechanisms in the therapeutic effects of IVIg in humans. We demonstrate that although several elements of both immune-modulatory pathways of IVIg are activated in humans, incorrect extrapolations from mice to men have been made on the molecular and cellular components involved in these cascades that warrant for critical re-evaluation of these anti-inflammatory mechanisms of IVIg in humans.

DEC-205/CD205+ dendritic cells are abundant in the white pulp of the human spleen, including the border region between the red and white pulp

The distribution of dendritic cells (DCs) and macrophages in the human spleen has received less attention than that of lymphocytes. Here we have addressed this problem with the human DEC-205/CD205 marker ('DEC'), which is an endocytic receptor on DCs that mediates efficient presentation of antigens. DEC was abundant on dendritic profiles in the white pulp but absent from the red pulp, the latter defined with antibodies to two antigens, mannose receptor/CD206 on sinusoidal lining cells, and macrosialin/CD68 on macrophages. Double staining with anti-DEC and anti-CD3 showed the expected concentration of DEC+ cells in the relatively small T-cell areas of the human spleen. DEC+ cells were also found in other regions of the white pulp. In all regions, the DEC+ cells were positive for major histocompatibility complex (MHC) class II and the CD11c integrin but largely immature, with low expression of B7-2/CD86 costimulator and DC-lysosome-associated membrane protein (LAMP)/CD208. When we concentrated on the perifollicular region between the red pulp and the marginal zone, we found macrophages that stained with antibodies to sialoadhesin/CD169 and DC-specific ICAM-3 grabbing non-integrin (SIGN)/CD209, and just inside these cells were DEC+ profiles. The DEC+ DCs were intertwined with cells that stained for the vascular addressin mucosal addressin cell adhesion molecule (MAdCAM). Therefore, anti-DEC-205/CD205 antibodies are useful for identifying DCs in human splenic white pulp and its border region with the red pulp.

Phenotypic differences between red pulp capillary and sinusoidal endothelia help localizing the open splenic circulation in humans

The distribution of capillaries, sinuses and larger vessels was investigated by immunohistology in paraffin sections of 12 adult human spleens using a panel of antibodies. Double staining for CD34 and CD141 (thrombomodulin) revealed that capillary endothelia in the cords of the splenic red pulp and at the surface of follicles were CD34(+)CD141(-), while red pulp sinus endothelia had the phenotype CD34(-)CD141(+). Only in the direct vicinity of splenic follicles did sinus endothelial cells exhibit both antigens. Thus, splenic sinuses do not replace conventional capillaries, but exist in addition to such vessels. The endothelium in arterioles, venules and larger arteries and veins was uniformly CD34(+)CD141(+). Anti-CD34 and anti-CD141 both additionally reacted with different types of splenic stromal cells. Differential staining of capillaries and sinuses may permit a three-dimensional reconstruction of serial sections to unequivocally delineate the "open" and "closed" splenic circulation in humans.

The splenic marginal zone in humans and rodents: an enigmatic compartment and its inhabitants

The role of the spleen in B memory cell development and maintenance is attracting increased attention. Studies in mice and rats have indicated that memory functions are associated with large B cells residing in the marginal zone (MZ) of the spleen. Although the cellular composition of the MZ is relatively well known in these species, controversies exist about the function of MZ B cells, their dependence on the presence of the spleen and the stage at which their development branches from that of recirculating follicular B cells. Additional confusion has arisen with respect to MZ B cells in humans, because the microscopic anatomy of the human splenic MZ differs decisively from that of rodents. Several recent publications indicate that the functional and migratory properties of human MZ B cells may be species-specific. The hypothesis derived from these publications and from our immunohistological observations implies that at least a major number of human splenic CD27(+) MZ B cells are migratory. Phenotypic data suggest a recirculation pathway between the spleen and mucosal tissues in humans.

Severe T-cell depletion from the PALS leads to altered spleen composition in common marmosets with experimental autoimmune encephalomyelitis (EAE)

Recent data suggest that the spleen is a crucial component of the immune system in the development of experimental autoimmune encephalomyelitis (EAE) in marmoset monkeys. Using immunohistochemistry, we investigated changes in the distribution of leukocytes in the spleen associated with clinical symptoms of EAE. Animals without EAE displayed well-developed T- and B-cell areas, germinal centers and red pulp. In contrast, a marked depletion of periarteriolar T cells with preservation of other elements was found in animals with clinical EAE. These findings suggest that immune responses within the spleen are impaired during a paralysing inflammatory process in the central nervous system.

The three-dimensional structure of human splenic white pulp compartments

The precise arrangement of B- and T-lymphocytes in the different compartments of the human splenic white pulp is still largely unknown. We therefore performed a 3D reconstruction of 150 serial sections of a representative adult human spleen alternately stained for CD3 and CD20. The results indicate that the T-cell regions of human spleens may be interrupted by B-cell follicles. Therefore, there is no continuous periarteriolar lymphatic T-cell sheath (PALS) around white pulp arterioles. An arteriole may be surrounded by T-lymphocytes at one level, then run across a follicle without any T-cells around, and finally re-enter a T-cell region. T- and B-cell compartments are intricately interdigitated in the human splenic white pulp. CD4(+) T-lymphocytes and the typical fibroblasts of the T-cell region may extend as a thin shell at the follicular surface within the marginal zone. On the other hand, IgD(++) B-cells continue from the follicular outer marginal zone along the surface of the T-cell region. Our findings indicate that the microanatomy of the splenic white pulp differs between humans and rodents. This may have consequences for the immigration of recirculating lymphocytes and for initial interactions among antigen-specific T- and B-lymphocytes.

Splenic histology and histopathology: an update

The spleen can be a troublesome specimen for the surgical pathologist, not only because experience with the range of "normal" splenic histology is limited by its rarity but also because there is an often a frustrating discordance between the patient's clinical condition and the perceived findings. Patients with a dramatic clinical presentation that points to splenic pathology ("hypersplenism" or marked splenomegaly) not infrequently have no discernable or have barely perceptible histologic abnormalities of the spleen. Similarly, patients whose spleens contain histologic findings that seem to deviate significantly from the "norm" (histiocytic proliferations, vasoformative lesions, stromal hyperplasia) may have no clinically detectable hematologic complaints. For most pathologists, the frame of reference for normal splenic histomorphology derives largely from experience with autopsy spleens and spleens removed for trauma or immune thrombocytopenia. These are all settings in which pre-existing disease, the immune status of the patient, and therapy influence the findings and--in cases in which fixation has been delayed--even the ability to make the findings. This review presents practical aspects of splenic development and immunoarchitecture and relates this to the pathologist's approach in evaluating the abnormal spleen and assists in resolving such discordances. Benign conditions that contrast with the subjects of subsequent articles in this issue are emphasized.

Splenic marginal zone atrophy and progressive CD8+ T-cell lymphocytosis in HIV infection: a study of adult post-mortem spleens from Côte d'Ivoire

AIMS

Progressive changes have been reported in lymph nodes in HIV infection, but few accounts describe altered splenic histology at different stages of the disease. Investigation of splenic changes accompanying the progressive CD4+ T-cell depletion that occurs in HIV infection could shed light on normal immunological interactions in this organ. Therefore, we assessed the amount and distribution of lymphoid tissue in spleens from adults with documented early or advanced HIV disease.

METHODS AND RESULTS

Immunohistochemistry was used to study splenic tissue collected in an extensive autopsy survey of HIV+ adults in West Africa. Compared with post-mortem spleens from HIV- West African adults and control UK spleens, those from HIV-infected patients showed severe atrophy of white pulp B- and T-cell compartments. In early and advanced HIV disease, marginal zone atrophy was significant. Peri-arteriolar lymphoid sheaths contained increased numbers of CD8+/CD45RO+ T-cells in advanced HIV disease. In red pulp, early and advanced cases showed a lymphocytosis of CD8+/CD45RO- T-lymphocytes.

CONCLUSIONS

Atrophic changes were more extreme in advanced than early HIV infection. Reduced marginal zone function possibly explains the known predisposition of HIV+ patients to infection by encapsulated bacteria. Possible immunological consequences of these CD8+/CD45RO+ (peri-arteriolar lymphoid sheaths) and CD8+/CD45RO- (red pulp) responses deserve further study. Comparison of West African and UK control spleens indicated that there were no major ethnic differences in spleen structure to prevent extrapolation of our results to European adults.

The perifollicular and marginal zones of the human splenic white pulp : do fibroblasts guide lymphocyte immigration?

We investigate the white pulp compartments of 73 human spleens and demonstrate that there are several microanatomical peculiarities in man that do not occur in rats or mice. Humans lack a marginal sinus separating the marginal zone (MZ) from the follicles or the follicular mantle zone. The MZ is divided into an inner and an outer compartment by a special type of fibroblasts. An additional compartment, termed the perifollicular zone, is present between the follicular MZ and the red pulp. The perifollicular zone contains sheathed capillaries and blood-filled spaces without endothelial lining. In the perifollicular zone, in the outer MZ, and in the T cell zone fibroblasts of an unusual phenotype occur. These cells stain for the adhesion molecules MAdCAM-1, VCAM-1 (CD106), and VAP-1; the Thy-1 (CD90) molecule; smooth muscle alpha-actin and smooth muscle myosin; cytokeratin 18; and thrombomodulin (CD141). They are, however, negative for the peripheral node addressin, the cutaneous lymphocyte antigen, CD34, PECAM-1 (CD31), and P- and E-selectin (CD62P and CD62E). In the MZ the fibroblasts are often tightly associated with CD4-positive T lymphocytes, whereas CD8-positive cells are almost absent. Our findings lead to the hypothesis, that recirculating CD4-positive T lymphocytes enter the human splenic white pulp from the open circulation of the perifollicular zone without crossing an endothelium. Specialized fibroblasts may attract these T cells and guide them into the periarteriolar T cell area.

Splenectomy in haemophagocytic lymphohistiocytosis: report of histopathological changes with CD19+ B-cell depletion and therapeutic results

The pathogenesis of haemophagocytic lymphohistiocytosis (HLH) in children without a known familial pattern of inheritance is often difficult to establish. Splenic enlargement, one of the main clinical findings in this disorder, has led to the use of splenectomy for uncontrollable coagulopathy, persistent cytopenia or both. This procedure is also thought to be a useful tool in making a differential diagnosis in cases of the immunochemotherapy-resistant HLH. We report here five cases of splenectomized childhood HLH, in which subsets of mononuclear spleen cells were analysed either by flow cytometry or immunohistochemistry, and the results were compared with those from cases of hereditary spherocytosis (controls). There was a statistically significant depletion of CD19+ B cells in the HLH cases (3.8 +/- 3.2% vs. 52.6 +/- 4.5%, P < 0. 0001) associated with an increase of T cells in three cases and of natural killer cells in another. The histopathological findings included atrophic white pulps, B-cell depletion with fibrosis and haemosiderosis in all five cases. Despite temporary therapeutic benefits, three of the HLH patients had a rapidly deteriorating post-splenectomy course and all three eventually died. These results demonstrate striking depletion of B cells in the enlarged spleens of children with HLH, which may be an intrinsic feature of HLH pathogenesis. Further study is needed to establish the therapeutic value of splenectomy in this disease.

High expression of CD23 in the proliferation centers of chronic lymphocytic leukemia in lymph nodes and spleen

Chronic lymphocytic leukemia (CLL) is a B-cell neoplasm composed of a heterogeneous mixture of cells, including small lymphocytes, prolymphocytes, and large transformed cells; these last cells appear to represent the proliferating compartment. CLL cells express, in addition to B cell markers, the transmembrane receptor CD23. CD23 functions as the receptor for IgE and also appears to play a role in controlling the growth and proliferation of lymphocytes. Its level of expression among the different cells in CLL has not been examined. In this study, we show that CD23 expression is much higher in the large transformed CLL cells than in the small lymphoid population. This may provide an explanation for the observed correlation between a circulating CD23 cleavage product (soluble CD23) and prognosis in CLL. In addition, we have shown that proliferation in splenic CLL occurs preferentially in the white pulp zones, even in cases in which both the white and red pulp are extensively infiltrated.

The species-specific structure of microanatomical compartments in the human spleen: strongly sialoadhesin-positive macrophages occur in the perifollicular zone, but not in the marginal zone

The microanatomical structure of human and rat splenic white pulp is compared, with special emphasis on the localization of the marginal zone occupied by immunoglobulin M (IgM)+ IgD-/dull B lymphocytes and its specialized macrophages. Our study reveals that in contrast to rats, the marginal zone of humans primarily exists in the vicinity of primary and secondary splenic follicles and that it is almost absent around the periarteriolar T-cell zones. We demonstrate that in humans there is an additional compartment, the perifollicular zone, located between the marginal zone and the red pulp. The perifollicular zone is a dynamic region of variable cellular and phenotypic composition, which can be regarded either as a part of the red pulp or of the follicles. In most cases the perifollicular zone appears as a compartment of the red pulp containing erythrocyte-filled spaces which differ from the typical red pulp sinusoids. Similar to the splenic cords, the perifollicular zone mostly harbours scattered B and T lymphocytes. However, sometimes B lymphocytes clearly predominate in the perifollicular area. In addition, strongly sialoadhesin-positive macrophages form sheaths around capillaries in the perifollicular zone. Such capillary sheaths are not observed in rats. In humans weakly sialoadhesin-positive macrophages are also present in the perifollicular zone and in the red pulp. In some specimens sialoadhesin is, however, strongly expressed by a large number of dispersed perifollicular macrophages. Interestingly, in striking contrast to rats, the human marginal zone does not contain sialoadhesin-positive macrophages and marginal metallophilic macrophages are also absent in humans. Thus, sialoadhesin-positive macrophages and IgM+ IgD- memory B lymphocytes both share the marginal zone as a common compartment in rats, while they occupy different compartments in humans. We show that the human splenic marginal zone does not contain a marginal sinus and assume that in humans the perifollicular region is the compartment where antigen and recirculating lymphocytes enter the organ.

Splenic micro-anatomical localization of small lymphocytic lymphoma/chronic lymphocytic leukemia using a novel combined silver nitrate and immunoperoxidase technique

Small lymphocytic lymphoma/chronic lymphocytic leukemia (SLL/CLL) may be histologically difficult to differentiate from reactive lymphoid hyperplasia (RLH) in the spleen. Because routine hematoxylin and eosin (H&E) staining delineates splenic microanatomy poorly, we have developed a method that simultaneously stains reticulin fibers and B-lymphocytes. B3 or formalin-fixed, paraffin-embedded archival splenic tissue with diagnoses of SLL/CLL (11 cases), RLH (10 cases), and trauma (seven cases) were studied using a novel silver nitrate immunoperoxidase (SNIP) double-staining technique. Gordon and Sweet's reticulin stain was followed by immunoperoxidase staining for B-lineage marker CD20 (Dakopatts, Carpinteria, CA) using the avidin-biotin method. This allowed us to clearly localize B cells to Malpighian bodies, periarteriolar lymphoid sheaths, sinuses, or cords. Features identified by SNIP found only in SLL/CLL, but not in RLH or traumatized spleens, were trabecular infiltration (eight of 11 cases), subendothelial infiltration (seven of 11 cases), and prominent sinus involvement (seven of 11 cases). One or more of these features were seen in 10 of 11 cases of SLL/CLL. Other distinguishing features were the percentage area occupied by B-lymphocytes in each section (SLL/CLL = 74%; RLH = 46%; traumatized spleens = 36%); and mean spleen weight (SLL/CLL = 1,603 g; RLH = 287 g; traumatized spleens = 126 g). We have found the SNIP technique to be superior to traditional H&E staining in identifying B cells in the context of splenic microanatomy.

Immunoarchitecture of normal human bone marrow: a study of frozen and fixed tissue sections

To provide baseline information on the immunoarchitecture of normal bone marrow, we studied cryostat-cut, frozen, and paraffin-embedded, fixed tissue sections prepared from 21 core biopsies of normal bone marrow obtained during bone marrow harvests for transplantation. A large panel of antibodies was applied that included, for frozen tissue, Leu-6 (CD1), T11 (CD2), Leu-3a (CD4), Leu-1 (CD5), Leu-2a (CD8), J5 (CD10), My7 (CD13), Leu-11 (CD16), B4 (CD19), B1 (CD20), B2 (CD21), Tac (CD25), My9 (CD33), T200 (CD45), NKH-1 (CD56), kappa and lambda chains, beta F1, Ki-67, HLA-DR, TQ1, and keratin, and for fixed tissue, leukocyte common antigen (CD45), L26 (CD20), LN1 (CDw75), LN2 (CD74), LN3, LN4, LN5, MB1 (CD45R), MB2, MT1 (CD43), MT2 (CD45R), UCHL1 (CD45R0), BM1, Ki-1 (CD30), Leu-M1 (CD15), lysozyme, KP1 (CD68), actin, S100, neuron-specific enolase, vimentin, and keratin. On fresh-frozen sections CD19 and CD2 were the most reliable and sensitive markers for B and T cells, staining 5% and 9% of marrow cells, respectively. Immunoglobulins generally showed heavy background staining, which frequently precluded an accurate assessment. The CD4 to CD8 ratio in the bone marrow was reversed from that of peripheral blood. On fixed tissues, leukocyte common antigen was found in 14% of the marrow cells, corresponding roughly to the lymphocyte population. L26, a pan-B-cell marker, stained 3% of the marrow cells. Among the other B-cell markers, LN1 and MB2 stained a large number of cells (40% to 70%), indicating reactivity with cells of the myeloid or erythroid series in addition to lymphocytes. Among the T-cell markers, UCHL1 and MT1 stained 66% and 50% of the cells, respectively, which could be explained by their cross-reactivity with myeloid cells. Nonspecific myelomonocytic markers (Leu-M1, KP1, and lysozyme) also showed reactivity in a high percentage of cells. No particular architectural distribution patterns of B or T lymphocytes were noted in either frozen or fixed bone marrow specimens. The results of this study provide normal baseline data for the immunohistologic application of hematopoietic and lymphoid markers on frozen or fixed bone marrow biopsy specimens.

Immunohistology of the human spleen after bone marrow transplantation for leukemia with special reference to the early post-transplantation period

Immunohistochemical investigations were undertaken on paraffin-embedded tissue from the spleens of seven patients who had died after bone marrow transplantation (BMT) for leukemia. Parallel investigations were undertaken on three surgically resected traumatically ruptured (but otherwise normal) spleens and three spleens removed at autopsy from accident victims. 1) Up to ten weeks after BMT, the splenic lymphoid tissue was extremely atrophic. Lymphoid follicles (LFs) and periarteriolar lymphatic sheaths (PALS) were completely absent. A considerable increase in lymphoid cells in the red pulp and formation of small LFs and PALS occurred only in the longest surviving patient, who had died 50 weeks after BMT. 2) B cells (L26+, 4KB5+, Ki-B3+) were almost completely absent in the early post-transplantation period and thus T cells (UCHL1+) represented the major constituent of the hypoplastic splenic lymphoid tissue. Considerable numbers of T cells were already found two weeks after BMT. T-immune-accessory reticulum cells (S-100 protein+) were found in the PALS of the controls, but were absent in three of the BMT recipients. The findings clearly reflect the marked immunodeficiency in the early post-transplantation period, during which many patients (4/7 in this study) die of opportunistic infections, and are in line with the fact that the earliest signs of reconstitution of the immune system have been found to occur at three months post-transplantation. Since six of our BMT recipients had suffered from graft-versus-host disease our findings probably do not fully correspond to those when the immune system undergoes undisturbed reconstitution.

Immunohistochemical assessment of splenic lymphocyte and macrophage subpopulations in patients with gastric cancer

In order to assess the effects of malignant tumors on the immune system, 25 spleens from patients with gastric carcinoma were studied by in situ immunohistochemical methods for lymphocyte subsets and cells of the mononuclear phagocyte system. Highly significant reductions of CD4+ T cells (P less than 0.001), Ki M2+ and Ki M-3+ MPS cells (P less than 0.02 and P less than 0.05), and a stage-dependent reduction of Ki 67+ B cell proliferation activity (P less than 0.05) were seen in spleens of patients with gastric cancer. These results, which were obtained by morphologic methods in a noninvolved lymphatic organ, reflect the systemic immunosuppressive and immunodepleting effects of malignant tumors that are probably mediated by tumor-associated cytokines.

Splenic marginal zone lymphocytes and related cells in the lymph node: a morphologic and immunohistochemical study

The marginal zone of the spleen contains a well-defined population of lymphocytes with an unknown function. The question is whether this cell population is unique to the spleen or is it also present in the lymph node. These cells have medium-sized nuclei and a moderate amount of cytoplasm. Immunohistochemistry and enzyme histochemistry revealed a marker pattern by which these cells could be distinguished from the lymphocytes of the mantle zone of the spleen: IgD-, CD23-, KiB3-, and alkaline phosphatase+. In the lymph node, the outer side of the follicular mantle contains a subpopulation of B lymphocytes with a similar morphology and the same marker pattern. This subpopulation differs from the marginal zone cells in the spleen in that it does not form a distinct zone. These cells are especially prominent in lymph nodes with fatty atrophy. Their relationship to other subpopulations of B lymphocytes and to malignant lymphomas is evaluated but remains questionable.

The spleen in Hodgkin's disease. An immunohistochemical study of lymphocyte subpopulations and macrophages

Lymphocyte subpopulations and macrophages in 16 spleens from patients with Hodgkin's disease were analysed immunohistochemically using monoclonal antibodies of the Leu and the Ki M series. In non-involved splenic tissue there is an increase of T-lymphocytes with an increased T-helper/T-suppressor cell ratio, while Ki M-1, -2, -3 and -5-positive, i.e. phenotypically different macrophages, are reduced. These results indicate that involvement of the spleen in Hodgkin's disease is accompanied by changes with respect not only to lymphocyte subpopulations but also to cells of the mononuclear phagocyte system. The immunodeficiency associated with Hodgkin's disease is probably not solely due to lymphocyte dysfunction, since the disease may lead, at least in the spleen, to alterations in macrophages and accessory cells and this may contribute to the impairment of cell-mediated immunity.

Cellular composition of the spleen after human allogeneic bone marrow transplantation

The cellular composition of the spleen has been assessed in 18 patients who died 15-326 days after receiving allogeneic marrow for leukaemia. The white pulp showed marked lymphocyte depletion with no germinal centres, very few B cells, and rare plasma cells. The marginal zone was unrecognizable but there were moderate numbers of T cells in the periarteriolar lymphatic sheaths (PALS), showing great variation in CD4/CD8 ratio. The percentage of CD4+ cells decreased with time post transplant. CD8+ cells were reduced in patients with graft-versus-host disease (GvHD) who also showed no increase in cells staining for activation markers. No T cells were detected expressing immature phenotypes and no differences were detected between patients who received marrow purged or unpurged of T cells. Macrophage numbers appeared normal. Extramedullary haemopoiesis (EMH) was predominantly in the red pulp greater than 30 days after transplantation but more commonly in the white pulp before then. Pyknotic cells were common in seven cases and appeared to be associated with EMH rather than GvHD. Chimaeric studies demonstrated small numbers of donor cells in the PALS at 26 days and larger numbers at 56 days.

The spleen in Felty's syndrome: a histological, morphometrical, and immunohistochemical study

A histological study employing morphometrical and immunohistochemical methods was performed in 3 spleens removed because of Felty's syndrome (FS). A comparison was made with control spleens and with spleens removed from patients with idiopathic thrombocytopenic purpura (ITP) or autoimmune hemolytic anemia (AIHA). In FS, the spleen is enlarged, mainly due to expansion of the red pulp. The sinuses are enlarged, too, and contain many macrophages. 2 of our specimens showed many hyperplastic germinal centers; the 3rd contained no germinal centers. Only in the former cases did splenectomy lead to an increase in the number of circulating granulocytes. Immunohistologically, FS spleens differed from the control, the ITP, and the AIHA spleens. The results have provided further evidence indicating that the pathogenesis of granulocytopenia in FS differs from that of autoimmune hematocytopenias, and have given rise to the hypothesis that, in FS, the spleen is the site of interaction between immune complexes and granulocytes.

Immunohistological demonstration of lymphocyte surface antigens in postmortem lymphoid tissues

The postmortem stability of cell antigens has hardly been studied. Using monoclonal antibodies (mabs) we examined the postmortem detectability of lymphocyte surface antigens in different lymphoid organs by comparing two sensitive, immunohistological staining procedures. To quantify the probable degree of autolysis of the tissues a score system was applied by taking into consideration the postmortem age as well as the core temperature of the corpses. The antigens examined generally proved to be very resistant to autolytic influences. Differences were found when comparing different mabs and with regard to the type of lymphoid tissue. The loss of immunohistological reactions was most extensive in the spleen whereas tonsils showed almost no qualitative alterations in staining patterns. Reactivity of mabs with postmortem tissues decreased in the following order: Dako CD22 and anti-Leu 4, anti-Leu 3a, anti-Leu 7, Dako T8. The mabs anti-Leu 7 and Dako-T8 frequently failed to demonstrate their respective antigens but no correlation between the loss of staining and the degree of autolytic decomposition (our score) could be detected. In general, postmortem tissues as well as tissues shock frozen after delay are suitable for qualitative immunohistology of those cells characterized by the mabs applied. The APAAP-method proved unequivocally to be the superior staining technique.

Hodgkin's disease in the spleen. A morphological study of 140 biopsy cases

140 spleens involved by untreated Hodgkin's disease were studied utilizing conventional histological methods. Regardless of the subtype of Hodgkin's disease, infiltrates of neoplastic cells were present either in the periarteriolar lymphoid sheath, the marginal zone or in both locations. Initially, infiltrates were confined to the splenic white pulp, later larger nodular foci of Hodgkin's disease developed by coalescence of several infiltrates. Neoplastic cells in Hodgkin's disease may reach the spleen by both retrograde lymphatic spread or the splenic artery; the presence of neoplastic cells in both T- and B-cell areas of the splenic white pulp implies a preference for Hodgkin's disease in the spleen with regard to a suitable microenvironment. This may be provided by certain macrophage subpopulations.