Human tonsil intraepithelial B cells: a marginal zone-related subpopulation

Immature B cell homing shapes human lymphoid tissue structure and function

Shortly after the emergence of newly formed human B cells from bone marrow as transitional cells, they diverge along two developmental pathways that can be distinguished by the level of IgM they express and migratory biases. Here, we propose that differential tissue homing of immature B cell subsets contributes to human lymphoid tissue structure and function.

Nodal reactive proliferation of monocytoid B-cells may represent atypical memory B-cells

BACKGROUND

Reactive lymphadenopathies such as toxoplasmosis and cytomegalovirus lymphadenitis are associated with monocytoid cell proliferation. Monocytoid cells are B-lymphocytes with an undetermined subset.

METHODS

Using digital spatial profiling whole transcriptome analyses, this study compared monocytoid and control B-cells. The B-cell subset of monocytoid cells was assigned according to gene expression profiles.

RESULTS

This study identified 466 differentially expressed genes between monocytoid and control B-cells. The cellular deconvolution algorithm identified monocytoid cells as memory B-cells instead of as naïve B-cells. A comparison of the upregulated genes revealed that atypical memory B-cells had the largest number of genes overlapping with monocytoid cells compared with other memory B-cell subsets. Atypical memory B-cell markers, namely TBX21 (T-bet), FCRL4 (IRTA1), and ITGAX (CD11c), were all upregulated in monocytoid cells. Similar to atypical memory B-cells, monocytoid cells exhibited (1) upregulated transcription factors (TBX21, TOX), (2) upregulated genes associated with B-cell inhibition (FCRL5, FCRL4) and downregulated genes associated with B-cell activation (PIK3CG, NFKB1A, CD40), (3) downregulated cell cycle-related genes (CDK6, MYC), and (4) downregulated cytokine receptors (IL4R). This study also analyzed the expression of monocytoid cell signature genes in various memory B-cell subsets. Atypical memory B-cells exhibited a gene expression pattern similar to that of monocytoid cells, but other memory B-cell subsets did not. Furthermore, monocytoid cells and marginal zone lymphomas differed in gene expression profiles.

CONCLUSION

Spatial transcriptomic analyses indicated that monocytoid cells may be atypical memory B-cells.

New insight into Epstein-Barr virus infection using models of stratified epithelium

Epstein-Barr virus (EBV) is a ubiquitous human pathogen that is transmitted in saliva. EBV transits through the oral epithelium to infect B cells, where it establishes a life-long latent infection. Reinfection of the epithelium is believed to be mediated by virus shed from B cells, but whether a latent reservoir can exist in the epithelia is unknown. We previously developed an in vitro organotypic model of stratified epithelium where EBV can readily replicate within the suprabasal layers of the epithelium following apical infection mediated by virus-producing B cells. Given that infected epithelial cells and cell-free virus are observed in saliva, we examined the ability of both of these to mediate infection in organotypic cultures. Epithelial-derived cell-free virus was able to infect organotypic cultures from the apical surface, but showed enhanced infection of B cells. Conversely, B cell-derived virus exhibited enhanced infection of epithelial cells. While EBV has been detected in basal cells in oral hairy leukoplakia, it is unknown whether EBV can be seen in undifferentiated primary keratinocytes in the basal layer. Undifferentiated epithelial cells expressed proposed EBV receptors in monolayer and were susceptible to viral binding and entry. Integrins, and occasionally ephrin A2, were expressed in the basal layer of gingiva and tonsil derived organotypic cultures, but the known B-cell receptors HLAII and CD21 were not detected. Following infection with cell-free virus or virus-producing B cells at either the apical or basolateral surface of preformed organotypic cultures, abundant infection was detected in differentiated suprabasal cells while more limited but readily detectable infection was observed in the undifferentiated basal cells. Together, our data has provided new insight into EBV infection in stratified epithelium.

Translating transitions - how to decipher peripheral human B cell development

During the last two decades our understanding of human B cell differentiation has developed considerably. Our understanding of the human B cell compartment has advanced from a point where essentially all assays were based on the presence or not of class-switched antibodies to a level where a substantial diversity is appreciated among the cells involved. Several consecutive transitional stages that newly formed IgM expressing B cells go through after they leave the bone marrow, but before they are fully mature, have been described, and a significant complexity is also acknowledged within the IgM expressing and class-switched memory B cell compartments. It is possible to isolate plasma blasts in blood to follow the formation of plasma cells during immune responses, and the importance and uniqueness of the mucosal IgA system is now much more appreciated. Current data suggest the presence of at least one lineage of human innate-like B cells akin to B1 and/or marginal zone B cells in mice. In addition, regulatory B cells with the ability to produce IL-10 have been identified. Clinically, B cell depletion therapy is used for a broad range of conditions. The ability to define different human B cell subtypes using flow cytometry has therefore started to come into clinical use, but as our understanding of human B cell development further progresses, B cell subtype analysis will be of increasing importance in diagnosis, to measure the effect of immune therapy and to understand the underlying causes for diseases. In this review the diversity of human B cells will be discussed, with special focus on current data regarding their phenotypes and functions.

Plasmodium falciparum malaria and invasive bacterial co-infection in young African children: the dysfunctional spleen hypothesis

Children with recent or acute malaria episodes are at increased risk of invasive bacterial infections (IBI). However, the exact nature of the malaria-IBI association is still unclear. Young children have an age-related spleen immunologic immaturity, mainly due to the still ongoing development of the marginal zone (MZ) B cell subset. By mounting a rapid antibody response against encapsulated bacteria, these cells are critical for the defence against highly pathogenic microorganisms that do not elicit classical T cell-dependent responses. There is increasing evidence that the anatomy of the spleen becomes disorganized during malaria infection, with complete dissolution of the MZ and apoptosis of MZ B cells. Correspondingly, a reduction in the frequency of the peripheral equivalent of the MZ B cells has been found in malaria endemic areas. A remarkable similarity exists in IBI susceptibility between African children with malaria and hyposplenic or splenectomized patients. However, studies specifically assessing the immune function of the spleen in controlling bacterial infections in young children with malaria are scarce.

Here, it is hypothesized that Plasmodium falciparum malaria infection constitutes a detrimental factor in the still immature spleen function of young children, resulting in a factually hyposplenic state during malaria episodes, putting children with malaria at a high risk to develop life-threatening bacterial infections. Studies to confirm or reject this hypothesis are greatly needed, as well as the development of affordable and feasible tools to assess the immune spleen function against encapsulated bacteria in children with malaria.

C-C chemokine receptor 1 expression in human hematolymphoid neoplasia

Chemokine receptor 1 (CCR1) is a G protein-coupled receptor that binds to members of the C-C chemokine family. Recently, CCL3 (MIP-1alpha), a high-affinity CCR1 ligand, was identified as part of a model that independently predicts survival in patients with diffuse large B-cell lymphoma (DLBCL). However, the role of chemokine signaling in the pathogenesis of human lymphomas is unclear. In normal human hematopoietic tissues, we found CCR1 expression in intraepithelial B cells of human tonsil and granulocytic/monocytic cells in the bone marrow. Immunohistochemical analysis of 944 cases of hematolymphoid neoplasia identified CCR1 expression in a subset of B- and T-cell lymphomas, plasma cell myeloma, acute myeloid leukemia, and classical Hodgkin lymphoma. CCR1 expression correlated with the non-germinal center subtype of DLBCL but did not predict overall survival in follicular lymphoma. These data suggest that CCR1 may be useful for lymphoma classification and support a role for chemokine signaling in the pathogenesis of hematolymphoid neoplasia.

Immunohistochemical organization patterns of the follicular dendritic cells, myofibroblasts and macrophages in the human spleen--new considerations on the pathological diagnosis of splenectomy pieces

There is reliable information about how changes in spleen histology are influenced by the relationship among B and T lymphocytes, macrophages, dendritic cells and myofibroblasts. Moreover, if it can be applied in the day-by-day pathology laboratory. This work intends to elucidate morpho-functional aspects of relationships of these cells in the different spleen compartments, how they are influenced by pathological conditions and how basic immunohistochemical techniques could optimize the histopathological diagnosis. We analyzed the usefulness of the monoclonal antibodies CD45RO, CD20, CD21, CD35, CD68, caldesmon, the smooth muscle alpha-actin type 1 (SMA-1) in 91 specimens. CD21(+) CD35(+) follicular dendritic cells were organized into three patterns in agreement with the immune condition of the lymphoid follicle. Smooth muscle alpha-actin type 1(+)and caldesmon(+)myofibroblasts draw two double rings: marginal-perifollicular and germinal-marginal. The latter is closely related to T-cells. CD68(+)red pulp macrophages had clear and linear configuration. The interruption of this CD68(+) linear pattern in splenic marginal zone lymphoma cases could be a criterion to differentiate it from reactive hyperplasia. CD45RO, CD20, CD21, CD68 and SMA-1 provide a basic and quality immunohistochemical battery for a better comprehension of the human spleen and could improve its histopathological diagnosis.

Phenotypic and functional heterogeneity of human memory B cells

Memory B cells are more heterogeneous than previously thought. Given that B cells play powerful antibody-independent effector functions, it seems reasonable to assume division of labor between distinct memory B cells subpopulations in both protective and pathogenic immune responses. Here we review the information emerging regarding the heterogeneity of human memory B cells. A better understanding of this topic should greatly improve our ability to target specific B cell subsets either in vaccine responses or in autoimmune diseases and organ rejection among other pathological conditions where B cells play central pathogenic roles.

IRTA1+ monocytoid B cells in reactive lymphadenitis show a unique topographic distribution and immunophenotype and a peculiar usage and mutational pattern of IgVH genes

The origin and function of monocytoid B cells (MBCs) are poorly understood. Taking advantage of their strong expression of IRTA1 (a receptor that is also associated with MALT marginal zone B cells), we have comprehensively analysed MBCs in 25 cases of lymphadenitis of different aetiologies, shedding new light on the topographical distribution, immunophenotype and IgV(H) gene usage and mutational profile of this B cell subset. IRTA1(+) MBCs, although predominantly located in the subcapsular and intermediary sinuses, were also observed scattered within germinal centres (GCs) in all lymphadenitis cases examined. The molecular characterization of IgV(H) genes revealed that IRTA1(+) MBCs residing in different areas of the lymph node (subcapsular sinus, intermediary sinuses and GCs) can be clonally related (with intraclonal variation), and that those located in GCs are consistently more mutated and selected for expression of a functional antigen receptor than those located in the sinuses. Moreover, by contrast, IRTA1(+) MBCs in GCs express the memory B cell marker CD27. Finally, in toxoplasmic lymphadenitis, the IRTA1(+) MBC population shows a highly preferential usage of the V(H) genes 3-7 and 3-30 (without any obvious peculiarity in their CDR3s), possibly suggesting that a superantigen expressed by Toxoplasma gondii may be involved in the early activation of this B cell subset.

K+ channel expression during B cell differentiation: implications for immunomodulation and autoimmunity

Using whole-cell patch-clamp, fluorescence microscopy and flow cytometry, we demonstrate a switch in potassium channel expression during differentiation of human B cells from naive to memory cells. Naive and IgD(+)CD27(+) memory B cells express small numbers of the voltage-gated Kv1.3 and the Ca(2+)-activated intermediate-conductance IKCa1 channel when quiescent, and increase IKCa1 expression 45-fold upon activation with no change in Kv1.3 levels. In contrast, quiescent class-switched memory B cells express high levels of Kv1.3 ( approximately 2000 channels/cell) and maintain their Kv1.3(high) expression after activation. Consistent with their channel phenotypes, proliferation of naive and IgD(+)CD27(+) memory B cells is suppressed by the specific IKCa1 inhibitor TRAM-34 but not by the potent Kv1.3 blocker Stichodactyla helianthus toxin, whereas the proliferation of class-switched memory B cells is suppressed by Stichodactyla helianthus toxin but not TRAM-34. These changes parallel those reported for T cells. Therefore, specific Kv1.3 and IKCa1 inhibitors may have use in therapeutic manipulation of selective lymphocyte subsets in immunological disorders.

Expression of the IRTA1 receptor identifies intraepithelial and subepithelial marginal zone B cells of the mucosa-associated lymphoid tissue (MALT)

IRTA1 (immunoglobulin superfamily receptor translocation-associated 1) is a novel surface B-cell receptor related to Fc receptors, inhibitory receptor superfamily (IRS), and cell adhesion molecule (CAM) family members and we mapped for the first time its distribution in human lymphoid tissues, using newly generated specific antibodies. IRTA1 was selectively and consistently expressed by a B-cell population located underneath and within the tonsil epithelium and dome epithelium of Peyer patches (regarded as the anatomic equivalents of marginal zone). Similarly, in mucosa-associated lymphoid tissue (MALT) lymphomas IRTA1 was mainly expressed by tumor cells involved in lympho-epithelial lesions. In contrast, no or a low number of IRTA1+ cells was usually observed in the marginal zone of mesenteric lymph nodes and spleen. Interestingly, monocytoid B cells in reactive lymph nodes were strongly IRTA1+. Tonsil IRTA1+ cells expressed the memory B-cell marker CD27 but not mantle cell-, germinal center-, and plasma cell-associated molecules. Polymerase chain reaction (PCR) analysis of single tonsil IRTA1+ cells showed they represent a mixed B-cell population carrying mostly mutated, but also unmutated, IgV genes. The immunohistochemical finding in the tonsil epithelial areas of aggregates of IRTA1+ B cells closely adjacent to plasma cells surrounding small vessels suggests antigen-triggered in situ proliferation/differentiation of memory IRTA1+ cells into plasma cells. Collectively, these results suggest a role of IRTA1 in the immune function of B cells within epithelia.

Focal follicular features in tonsillar diffuse large B-cell lymphomas: follicular lymphoma with diffuse areas or follicular colonization

Focal follicular features in diffuse large B-cell lymphomas (DLBCLs) are bound to raise the question of follicular lymphoma (FL) with diffuse areas, because the diagnosis of FL is based on the presence of follicular areas, even though focal. We report 7 cases of primary tonsillar DLBCLs with focal follicular features that presented with morphologic, immunohistochemical, and biological features distinct from those of FL. Histologically, these tumors were characterized by involvement of pericryptal follicles with adjacent dominant diffuse areas. Monomorphous large tumor cells were evenly spaced with abundant, often clear cytoplasm, and blastoid nuclei often with a delicate nuclear membrane. Importantly, residual germinal centers (GCs) were present in the form of either an intrafollicular GC remnant or an isolated GC in the midst of diffuse tumor. An extrafollicular and/or parafollicular growth pattern was also observed. Bcl-6 staining revealed a predominantly sporadic occurrence of Bcl-6(+) cells, comprising <50% of tumor cells, and none displayed diffusely dense collections (>75%) of Bcl-6(+) tumor cells characteristic of the GC or FL. Staining for CD10 was negative in 6 cases. Five of 7 patients were younger than 60, the median age of other patients with primary tonsillar DLBCL. No extratonsillar involvement was seen at 18 months after diagnosis. After chemotherapy or radiotherapy, complete remission was achieved with ease in all patients, but 2 patients who were treated with chemotherapy alone relapsed at 24 and 30 months. In conclusion, tonsillar DLBCL includes a small (10%) but distinct subgroup that warrants distinction from FL with predominant diffuse areas or de novo DLBCL. It appears that the focal follicular features in tonsillar DLBCL likely represent follicular colonization of marginal zone B-cell lymphoma, probably high-grade, if the possibility of FL is excluded.

Marginal zone B cell lymphomas of Waldeyer's ring--a report of two tonsillectomy cases resembling histomorphological features of inflammatory lesions

We identified two cases of lymphoma of the mucosa-associated lymphoid tissue (MALT) type in 11 tonsillectomy specimens of primary B cell lymphoma of Waldeyer's ring. Both patients were Japanese females presenting with bilateral enlargement of the palatine tonsils. One had a history of chronic otitis media. In that case, the lesion was characterized by an extrafollicular growth pattern with marginal zone-like arrangement. The tumor was mainly composed of medium-sized cells with round or indented nuclei with scant cytoplasm (centrocyte-like cells). In the other patient, most tumor cells were mature plasma cells, plasmacytoid cells, proplasmacytes, and immunoblasts with scattered centrocyte-like cells. Tropism of tumor cells for the epithelium was noted in both lesions. Primary marginal zone B cell lymphoma of the MALT type arising from Waldeyer's ring has rarely been reported in the literature, causing certain diagnostic problems. Various florid reactive lymphoproliferative disorders, including chronic tonsillitis and infectious mononucleosis, should be differentiated from this type of primary Waldeyer's ring lymphoma.

Marginal zone cell lymphoma--an update on recent advances

The marginal zone represents one of the distinct compartments of the B-cell area in lymphoid tissues. It is especially well developed in the spleen and in Peyer's patches of the gut, but not in lymph nodes, with the exception of the ones in the mesenterium. However, the pronounced proliferation of so-called 'monocytoid B-cells' that may be seen in some inflammatory conditions of the lymph node may be regarded as a nodal reactive marginal zone cell expansion. The cellular compositions of the marginal zone and the monocytoid B-cell proliferation are similar and both show a heterogeneous population of B-cells, of which the functions are being slowly unravelled. Neoplasms originating in the marginal zone have been recognized in the past and are listed in the REAL classification as marginal zone B-cell lymphomas including extranodal MALT-type lymphomas, splenic marginal zone lymphomas and nodal (monocytoid) marginal zone lymphomas. Marginal zone cell lymphomas display a broad morphological spectrum, which is reflected by the heterogeneity of the cellular composition and the variation in the growth pattern of the lymphoma, but is independent of the anatomical site. All three marginal zone cell lymphomas share immunophenotypic, genetic and chromosomal similarities which will be discussed. The morphologic features are dealt with only briefly as they have been extensively discussed elsewhere.

Heterogeneity of tonsillar subepithelial B lymphocytes, the splenic marginal zone equivalents

The VH4 genes expressed by both resting and in vivo-activated subepithelial (SE) B cells from human tonsils were studied. Resting SE B cells were subdivided according to the presence (IgDlow) or absence (IgM-only) of surface IgD. CD27 was abundant on activated SE B cells and low on resting IgM-only B cells. Resting IgDlow SE B cells could be subdivided into CD27low and CD27high cell fractions. Resting IgDlow SE B cells displayed VH4 genes with a substantial number of mutations (13/29 of the molecular clones were mutated), whereas 25/26 of the clones from resting IgM-only SE B cells were unmutated. Moreover, mutated VH4 genes were detected mainly within the CD27high cell fraction of the IgDlow SE B cells. Several identical unmutated VH4DJH sequences (11/32) were found in different molecular clones from resting IgM-only SE B cells, suggesting local cellular expansion. Both unmutated (14/25) and mutated (11/25) sequences were found in mu transcripts of activated SE B cells. Extensive mutation was observed in the gamma transcripts of activated SE B cells. Therefore, SE B cells are heterogeneous, being comprised of B cells with mutated Ig VH4 genes, that are Ag-experienced B cells, and a subset of B cells with unmutated VH4 genes that are either virgin cells or cells driven by Ags that did not induce or select for V gene mutations.

Marginal zone B-cell lymphomas including mucosa-associated lymphoid tissue type lymphoma (MALT), monocytoid B-cell lymphoma and splenic marginal zone cell lymphoma and their relation to the reactive marginal zone

The marginal zone of the B follicle represents a well-defined compartment of the B area. Its cellular composition is distinct from that of the follicle centre, from which it also differs in its functional role in the immune response. Several newly identified lymphoma entities, e.g. extranodal MALT type lymphoma, nodal monocytoid B-cell lymphoma and splenic marginal zone B-cell lymphoma, display in common a very peculiar organoid growth pattern reminiscent of the marginal zone. Moreover, their neoplastic components share morphologic and phenotypic similarities to the cellular components of the marginal zone. The clinical characteristics of these various marginal zone cell lymphomas may differ depending of the organ which is involved. Nevertheless, they all share common cytogenetic abnormalities suggesting a common pathogenesis.

Active replication of HIV-1 at the lymphoepithelial surface of the tonsil

Cells that are infected with HIV-1 were visualized at the mucosal surface of the nasopharyngeal and palatine tonsils in 14 specimens from patients with CD4+ T-cell counts of 200 to 900/microliter and 2- to 10-year histories of HIV-1 infection. Most of the cells with intracellular HIV-1 protein were small but multinucleated. The majority of these syncytia could be double labeled for HIV-1 RNA and a dendritic cell marker S100. In the palatine tonsil, the infected cells were not found in the stratified squamous epithelium that is adjacent to the pharynx. Instead, the S100+ infected syncytia were localized to the surface of tonsil invaginations or crypts. This mucosa, termed lymphoepithelium, contains antigen-transporting M cells that lie above regions where S100+ dendritic cells are juxtaposed with CD4+ lymphocytes. Likewise, infected cells were found in lymphoepithelium and not respiratory epithelium of nasopharyngeal tonsils or adenoids. We propose that lymphoepithelia, the histological term that describes the specialized regions where antigens access mucosa-associated lymphoid tissue, are sites where HIV-1 replication can be enhanced in syncytia derived from dendritic cells.

Nasal lymphoid tissue, intranasal immunization, and compartmentalization of the common mucosal immune system

Mucosal application of vaccines with an appropriate adjuvant can induce immune responses at both systemic and mucosal sites, and therefore may prevent not only infectious disease, but also colonization of mucosal surfaces. Intranasal is more effective than intragastric immunization at generating earlier and stronger mucosal immune response. Nasal lymphoid tissue (NALT) and its local draining lymph nodes may retain long-term immune memory. IgA isotype switching, and the differentiation and maturation of IgA antibody-secreting cells (ASC) may occur before these cells migrate out of NALT, whereas IgG ASC responses require passage of the cells through draining lymph nodes of the NALT. Knowledge of whether immune memory cells can recirculate to and reside in the inductive sites other than their origin after encountering antigen will be helpful for understanding the compartmentalization of the common mucosal immune system as well as for determining the best route for delivering a mucosal vaccine against a particular pathogen.

Subepithelial B cells in the human palatine tonsil. I. Morphologic, cytochemical and phenotypic characterization

This study describes the purification of a subset of tonsillar B cells which share phenotypic, morphologic and cytochemical features with subepithelial (SE) B cells. These cells, which represented the 5-10% of the total tonsillar B cells, were found in the Percoll gradient fraction of highest density, together with resting follicular mantle (FM) B cells. The latter B cells, however, expressed surface CD5 and could be removed by an immune rosetting procedure. The remaining small CD5- B cells had a surface phenotype (IgM+, IgD+, CD23-, CD38+/-, CD10-, CD44+) that was different from that of FM (IgM+, IgD+, CD23+, CD39+, CD38-, CD10-, CD44+2) and of germinal center (GC) (CD23-, CD39-, CD38+, CD10+, CD44+/-, IgG+) B cells isolated from the same cell suspensions. Furthermore, the absence of surface activation markers (CD71 and CD69) and of surface IgG allowed us to distinguish small CD5- B cells from activated and memory cells migrating within Percoll fractions of lower density. In situ immunohistochemical studies revealed that B cells with an identical phenotype as that of small CD5- B cells could be detected predominantly in the SE region (lamina propria) of the tonsil, and also within the epithelium lining the cryptae. This area was also comprised of a relatively minor proportion of activated B cells, not found in the small CD5- B cell fraction owing to the separation procedure used. Consistent with the notion that the SE area could be a site of B cell activation was also the presence of activated macrophages and of plasma cells. Thirty to forty percent of small CD5- B cells isolated in suspension were positive for the endogeneous alkaline phosphatase (ALP) activity. In contrast, only a few FM B cells were ALP+, while GC cells were consistently ALP-. In situ studies also demonstrated a prevalent expression of ALP activity by the B cells in the SE area. At the ultrastructural level, small CD5- B cells were clearly different from both FM and GC B cells. They displayed a cytoplasm more extended than that of FM B cells with abundant endosomes and plasma membrane projections, and a speckled pattern of nuclear heterochromatin distribution. When fixed tissue sections were examined, cells with identical ultrastructural features could be demonstrated in the tonsillar lamina propria. Collectively, the above data demonstrate an identity of features between the small CD5- B cells isolated in suspension and SE B cells analyzed in situ. Since tonsillar SE B cells are generally thought to represent the homolog of the extrafollicular B cells (including those of the splenic marginal zone), these studies may provide new opportunities for functional studies on this so far incompletely characterized B cell subset.

Subepithelial B cells in the human palatine tonsil. II. Functional characterization

This study investigates the main functional features of subepithelial (SE) B cells and compares them with those of purified germinal center (GC) and follicular mantle (FM) B cells isolated from the same tonsils. Unlike FM B cells, SE B cells failed to produce polyspecific antibodies in vitro; unlike GC B cells, SE B cells expressed high levels of Bcl-2 and failed to undergo spontaneous apoptosis in vitro. The most striking function of SE B cells was their ability to produce IgM antibodies to T cell-independent type-2 (TI-2) (but not to TI-1) antigens (Ag). These antibodies could not be detected when both FM and GC B cells were stimulated with TI-2 Ag in vitro. Moreover, B cells isolated from peripheral blood were unable to mount a response to TI-2 Ag. The latter finding is consistent with the observation that B cells with the phenotypic features of SE B cells were virtually absent in the peripheral blood and emphasizes the notion that SE B cells belong to a subset of non-recirculating B cells. SE B cells were by far superior to FM B cells in mixed lymphocyte reaction (MLR) stimulation of allogeneic T cells in vitro, although they were not as efficient as dendritic cells (DC). In order to stimulate T cells efficiently, SE B cells had to be exposed to anti-mu antibody, a treatment which induced expression of activation markers such as CD80, CD86, CD69 and CD39, usually absent in resting SE B cells. CD80 and CD86 molecules expressed by SE B cells participated in the chain of events required to promote the proliferation of allogeneic T cells as demonstrated by inhibition tests with the appropriate mAb. The expression of CD80 and CD86 by anti-mu-treated SE B cells was not, however, the sole explanation for their good antigen presenting capacities since the exposure of FM B cells to anti-mu antibody also induced expression of these surface structures. Nevertheless, these cells failed to become good MLR stimulators. Collectively, the above data contribute further to the characterization of a distinct subset of tonsillar B cells which resemble, both phenotypically and functionally, the B cells of the splenic marginal zone.

Sequence analysis of rearranged IgVH genes from microdissected human Peyer's patch marginal zone B cells

The Peyer's patches of the terminal ileum are a source of IgA plasma cells in the intestinal lamina propria of experimental animals. They are also thought to harbour IgA memory cells. However, the microanatomical location of Peyer's patch memory cells, and whether they are also present in man is not known. Human Peyer's patches have a pronounced marginal zone (MGZ) of sIgD-negative B cells. In this study we analysed the sequence of polymerase chain reaction-amplified, rearranged IgVH genes from microdissected MGZ B cells, to determine whether this is a site of B-cell memory in Peyer's patches. We observed that the majority of Peyer's patch MGZ B cells contain heavily mutated IgVH genes and are therefore clearly memory B cells. Sequences of rearranged mutated genes in the MGZ have a pattern of replacement and silent mutations expected of selected products of the affinity maturation process. Related clones, with identical CDR3 but different patterns of mutation, are seen. This suggests that either these memory cells are formed as the germinal centre selection process proceeds, or a memory cell has re-entered the germinal centre for further rounds of mutation. Interestingly, in one patient, the MGZ in the Peyer's patches also contains a proportion of B cells with unmutated IgVH 4.21 genes.

Lymphoid changes of the nasopharyngeal and palatine tonsils that are indicative of human immunodeficiency virus infection. A clinicopathologic study of 12 cases

We report 12 cases in which the histomorphologic changes of the nasopharyngeal tonsils (adenoids) or palatine tonsils suggest infection with the human immunodeficiency virus (HIV). The patients included 10 men and two women, aged 20 to 42 years (median, 33 years). The clinical presentation included airway obstruction, pharyngitis, fever, and a tonsillar or adenoidal mass lesion. Histologic evaluation of the excised adenoids or tonsils in 10 of the cases demonstrated a spectrum of changes including florid follicular hyperplasia, follicle lysis, attenuated mantle zone, and the presence of multinucleated giant cells (MGC). The latter characteristically localized adjacent to the surface or tonsillar crypt epithelium. Two of the 12 cases showed marked lymphoid depletion with absent germinal centers, plasmacytosis, and stromal vascular proliferation. Immunohistochemical evaluation for HIV p24 core protein showed reactivity in 10 of 12 cases localized to follicular dendritic cell network (FDC), the MGC, scattered interfollicular lymphoid cells, and cells identified within the surface or crypt epithelium. Localization of viral RNA by in situ hybridization paralleled the HIV p24 immunohistochemical findings. Additional significant findings included the presence of both CD-68 and S-100 protein in the MGC and the presence of S-100 protein in dendritic cells. Other than HIV, no microorganisms were identified. At the time of presentation, eight patients were not known to be a risk for HIV infection, nor were they known to be HIV infected or suffering from AIDS. In these patients, HIV infection was suspected on the basis of the histologic changes seen in the resected tonsillar and adenoidal tissue. Serologic evaluation (by enzyme-linked immunosorbent assay), confirmed the presence of HIV infection. Our findings suggest the possibility of HIV dissemination through the upper aero-digestive tract mucosa via target cells, such as intraepithelial dendritic cells, submucosal macrophages, and T-lymphocytes. Subsequent presentation of viral antigens to the tonsillar and adenoidal lymphoid tissues results in enlargement of these structures that clinically may simulate a neoplastic proliferation but causes histomorphologic changes that are highly suspicious for HIV infection even in asymptomatic HIV-positive patients.

The lymphoepithelial organization of the tonsil: an immunohistochemical study in chronic recurrent tonsillitis

Interactions between leukocytes and crypt epithelium were extensively investigated in 12 cases of chronic recurrent tonsillitis, using immunohistochemistry and cytofluorimetric analysis of cell suspensions. Intraepithelial leukocytes are a mixed cell population composed of 50 per cent CD20-positive B lymphocytes, 40 per cent T lymphocytes with a 2.7 CD4/CD8 ratio, and 10 per cent CD68-positive macrophages. About 4 per cent of intraepithelial leukocytes are proliferating cells, as indicated by Ki-67 staining. Leukocyte infiltration is associated with expression on epithelial cells of the adhesion molecules ICAM-1 and VCAM-1. Crypt epithelium is supported by a basement membrane showing frequent interruptions and connected with the reticular stroma of the lymphoid tissue, which was stained for fibronectin, tenascin, collagen, and laminin. Extracellular matrix (ECM) distribution was correlated with integrin expression on B and T lymphocytes. It was found that the ECM was arranged differently in the follicles and in the extrafollicular area and that B and T lymphocytes exhibited different patterns of integrin expression.

Reticular crypt epithelium and intra-epithelial lymphoid cells in the hyperplastic human palatine tonsil: an immunohistochemical analysis

Extensive immunohistochemical analyses of the hyperplastic human palatine tonsil disclosed variegated B cell phenotypes on the lymphoid cells among the crypt epithelium. The reticular epithelial network was evident by cytokeratin immunostaining. The reticular epithelium near the crypt lumen was positive for lysozyme. Secretory component was negative, while HLA-DR was frequently expressed. Intramucosal small lymphocytes, densely distributed in the luminal side, consisted mainly of B cells expressing CD19, CD20, CD21, CD22, CD45R, CD74, DBB42, HLA-DR, HLA-DQ, bcl-2 protein and surface IgM. Some B cells revealed mantle zone phenotypes (surface IgD+, CD5+, CD24+, DBA44+, CD10-, DNA7-). Cells of germinocyte phenotype (CD10+, DNA7+) were sparsely seen. A good number of intramucosal lymphoid cells were further labeled for CD11b, a phenotype of so-called B-1 cells. Plasma cells were clustered within the basal half. IgG was their major immunoglobulin class, followed by IgA, IgM and IgD classes. A smaller number of T cells (CD2+, CD3+, CD5+, CD45RO+, TCR alpha beta+) were identified among the epithelium. CD4+ cells predominated over CD8+ cells. TCR gamma delta+ cells were rare. Macrophages (CD68+), dendritic histiocytes (S-100 protein+, CD1+), and natural killer cells (CD16+ or CD57+) were also dispersed. Another unique feature of this lymphoepithelial complex was the existence of HLA-DR- intramucosal intramucosal microvasculature, where lymphocyte recirculation was suggested. Proliferating cell nuclear antigen was detected commonly in the epithelial cells but rarely in the lymphoid cells. Possible lymphoepithelial interactions and morphologic similarities to the thymic medulla are discussed.

Low-grade B-cell lymphoma of mucosa-associated lymphoid tissue type in Waldeyer's ring

Amongst a total of 329 cases of low-grade B-cell lymphoma of Waldeyer's ring, we identified 12 cases that corresponded histomorphologically to low-grade B-cell lymphoma of mucosa-associated lymphoid tissue (MALT) type. These lymphomas are characterized by an extrafollicular growth pattern, often with a marginal zone-like arrangement, and by the centrocyte-like morphology of the tumour cells. They have not been described previously in this location. They predominantly affected the palatine tonsil. Ten cases were primary lymphomas of Waldeyer's ring. In two cases there was a simultaneous high-grade component. Two cases showed regional spread to cervical lymph nodes, but there was no widespread nodal involvement at the time of diagnosis. Immunohistochemically, all cases displayed B-cell markers and light chain restriction. Tropism of tumour cells for the epithelium was a consistent finding. In two cases involvement of Waldeyer's ring was secondary; in one of them the primary tumour was a gastric low-grade B-cell lymphoma of MALT type and in the other a high-grade B-cell non-Hodgkin's lymphoma of the stomach. These findings indicate that low-grade B-cell lymphomas of MALT type occurring in Waldeyer's ring should be included amongst the tumours of the MALT system. We surmise that in Waldeyer's ring such tumours are derived from the marginal zone, as has already been postulated for similar gastric tumours.

Waldeyer ring lymphomas. A clinicopathological study of 79 cases

Waldeyer ring lymphomas belong to a category of tumours which has not yet been fully defined. Their relation to mucosa-associated lymphoid tissue (MALT) and other extranodal lymphomas remains largely unknown. We performed a clinicopathological retrospective study of 79 patients, and compared them with a series of MALT and nodal lymphomas. Tumours from the nasopharynx and palatine tonsil showed similar histological profiles, with a predominance of large B-cells. Centroblastic lymphomas constituted the largest group (n = 45), followed by those of centrocytic type (9) with smaller groups of centroblastic-centrocytic (5) and Hodgkin's lymphomas (2). Three monocytoid B-cell lymphomas were identified. Only one case could be classified as MALT lymphoma. The frequency of bcl-2 expression in large B-cell tumours of Waldeyer's ring has an intermediate range between large B-cell lymphomas occurring in mucosal and nodal locations. Epitheliotropism was present in all low-grade cases, and was therefore not a useful marker in the identification of potential MALT lymphomas in contrast with other mucosal sites. Comparative survival studies showed significant overall differences between Waldeyer ring lymphomas, MALT and nodal cases. These disappeared after taking stage and histological grade into account. We conclude that Waldeyer ring lymphomas show distinctive features, mainly in terms of histological distribution and immunophenotype. The key factor determining their behaviour could be their different spreading capability. These findings suggest that extranodal lymphomas are heterogeneous, and indicate the need for additional efforts to clarify this.

Malignant lymphoma of Waldeyer's ring. A histological and immunohistochemical study

The histopathological and immunohistological features of non-Hodgkin's lymphoma limited to the Waldeyer's ring were studied in 22 Japanese patients using a panel of T- and B-cell markers on paraffin-embedded sections. All cases showed a diffuse growth pattern. Twenty cases were B-cell lymphomas and two were T-cell lymphomas. In contrast to the primary malignant lymphomas of the nasal cavity and paranasal sinuses, in which T-cell neoplasms are more frequently seen, the majority of the primary Waldeyer's ring lymphomas were B-cell neoplasms. Sixteen of the 20 cases of B-cell lymphoma were centroblastic lymphomas, and the monomorphic variant comprised the majority of these; the other three B-cell lymphomas were immunocytomas. Two of the T-cell lymphomas showed morphological features of angiocentric lymphomas.