T cells and follicular dendritic cells in germinal center B-cell formation and selection

Summary: Germinal centers (GCs) are specialized microenvironments formed after infection where activated B cells can mutate their B-cell receptors to undergo affinity maturation. A stringent process of selection allows high affinity, non-self-reactive B cells to become long-lived memory B cells and plasma cells. While the precise mechanism of selection is still poorly understood, the last decade has advanced our understanding of the role of T cells and follicular dendritic cells (FDCs) in GC B-cell formation and selection. T cells and non-T-cell-derived CD40 ligands on FDCs are essential for T-dependent (TD) and T-independent GC formation, respectively. TD-GC formation requires Bcl-6-expressing T cells capable of signaling through SAP, which promotes formation of stable T:B conjugates. By contrast, differentiation of B blasts along the extrafollicular pathway is less dependent on SAP. T-follicular helper (Tfh) cell-derived CD40L, interleukin-21, and interleukin-4 play important roles in GC B-cell proliferation, survival, and affinity maturation. A role for FDC-derived integrin signals has also emerged: GC B cells capable of forming an immune synapse with FDCs have a survival advantage. This emerges as a powerful mechanism to ensure death of B cells that bind self-reactive antigen, which would not normally be presented on FDCs.     

In situ detection of activated cytotoxic cells in follicular lymphomas.

The presence of cytotoxic cells and their activation status were analyzed in tissue sections of 26 follicular lymphomas. To this end, expression of the perforin and granzyme B genes was studied by in situ hybridization experiments, and expression of the TIA-1 antigen was analyzed by immunohistochemistry. Cells expressing the granzyme B gene and the perforin gene were detected in all cases. Their density was, however, highly heterogeneous from case to case, ranging from 160 to 7,040 positive cells/cm2 of tissue sections. TIA-1-positive cells were also evidenced in the 10 follicular lymphomas tested. Virtually all cytotoxic cells were located in interfollicular areas. Double labeling immunochemical experiments showed that most cytotoxic cells belonged to the CD8+ T lymphocyte population, although few CD4+ T lymphocytes and CD56+ natural killer cells also expressed the TIA-1 antigen. These findings show that development of a malignant B lymphocyte proliferation is associated with a host-derived immune response involving intratumoral cytotoxic T lymphocytes. Further studies comparing the density of such cells with the final outcome are required to determine whether the intensity of this immune response has a prognostic value.     

Study of the reactive dendritic cells in small B-cell lymphoproliferations of the skin

Distinguishing between low-grade primary cutaneous B-cell lymphoma (LG-pCBCL) and cutaneous lymphoid hyperplasia (CLH) based on histological features is often difficult. CLH lesions contain numerous reactive cells of the histiocyte lineage [Langerhans cells (LC), dermal dendritic cells (DDC), and macrophages], which are also often present in CBCL. The aim of this study was to determine whether immunohistochemical detection of those cells could help differentiate between CLH and LG-pCBCL. We determined the percentages of those histiocytic cells in the dermal infiltrates of 45 cases of cutaneous lymphoproliferations comprising 16 CLH and 29 LG-pCBCL (19 follicle-center cell lymphomas and 10 marginal zone lymphomas) by immunohistochemical labeling with antibodies to CD1a, FXIIIa, and CD68 to respectively detect LC, DDC, and macrophages. To avoid observer-dependent bias, an automated morphometric analysis method was used to recognize immunoreactive cells and calculate their percentages within the infiltrate. FXIIIa⁺ cells were significatively more frequent in CLH than in LG-pCBCL, whereas CD1a⁺ and CD68⁺ cell frequencies were comparable in the two groups. The results of our study suggest that DDC might play an important role in the genesis of cutaneous lymphomas.     

Morphoimmunohistochemical differential diagnosis of B-cell lymphomas

The paper considers the stages of B-cell differentiation at the level of central (bone marrow) and peripheral (lymph node) organs of the immune system. The immunophenotype of B-cell lymphoid tumors and their "normal" cell analogues was compared, by taking into account 4 stages of B-cell differentiation: bone marrow B-cell precursors, mature B-cell, B-cell with follicular differentiation, postfollicular B-cell. Algorithms of immunohistochemical differential diagnosis of B-cell lymphomas are proposed when their morphological patterns are similar.     

Neoplastic plasma cells in follicular lymphomas

Summary Six cases of follicular lymphoma contained an abundant plasma cell component. With immunoperoxidase techniques, this was found to demonstrate monotypic cytoplasmic marking for either K or L Ig light chain in five cases, and for IgA heavy chain only in one case. A histogenetic relationship between follicular center cells and plasma cells was suggested by cell forms morphologically intermediate between these two types and by monotypic plasma cells in the neoplastic follicles. The progressive differentiation of follicular center cells into Ig-secreting cells in these cases is likely to be the result of an alteration of the immunoregulatory mechanisms that usually block the differentiation of follicular lymphomas.Four of our patients presented with disseminated disease, three had extranodal presentation and four manifested serum paraproteins. Their median survival was 40 months; two of them died of disease. The published data and our own suggest that follicular lymphoma with plasmacytic differentiation is a malignancy of intermediate grade, with survival and clinical features closer to lymphoplasmacytic/lymphoplasmacytoid lymphoma (LP immunocytoma) than to follicular lymphoma.Dedicated to Professor Dr. Karl Lennert, on the occasion of his 65th birthday     

Immunohistochemical analysis of small plaque parapsoriasis: involvement of dendritic cells

Small plaque parapsoriasis (SPP) is one of the cutaneous T-cell lymphoproliferative disorders. The aim of the present study was to show the antigenic profile of a subset of dendritic cells and lymphocytes in SPP in comparison with normal cells to provide data on the role of these two cell types in the pathogenesis of SPP. Skin biopsy specimens of lesions were obtained from 8 patients with SPP. Biopsies of the healthy skin from 9 control individuals were also analyzed. Immunohistochemistry was performed on the frozen tissue sections to reveal binding of anti-HLA Class II, anti-CD1a, anti-CD4, anti-CD8, anti-CD44, anti-CD45, and anti-CD68 monoclonal antibodies. There was a statistically significant increase in the number of CD1a(+), Langerhans cells (LCs), HLA-DR-immunoreactive and, CD1a-positive dermal dendritic cells and CD68(+) macrophages in the SPP group (p=0.008, 0.008, 0.002 and <0.0009, respectively). The number of lymphocytes positive for CD4, CD8 and CD45 was significantly higher than normal in the SPP group (p=0.015, <0.0009 and <0.0009, respectively). Our study demonstrates that both peptide- and lipid-based antigens are involved in the persistent antigenic exposure in SPP. Dendritic cells play a pivotal role in SPP by presenting antigens by both LC and dermal dendritic cells via MHC Class II and CD1a molecules. The CD68(+) macrophages are thought to be involved in the immune response in this pathology as an antigen-presenting cell.     

Distribution pattern of follicular dendritic cells in low grade B-cell lymphomas of the gastrointestinal tract immunostained by Ki-FDC1p: a new paraffin-resistant monoclonal antibody

This study surveyed 97 cases of low grade B-cell lymphoma (LGBL) of the gastrointestinal tract (GIT) by conventional morphology and immunohistochemistry, focusing on the most frequent subtype: the so-called LGBL of the mucosa-associated lymphoid tissue (MALT). Special reference was made to the follicular dendritic cells (FDCs) selectively visualized by a new paraffin-resistant monoclonal antibody Ki-FDC1p. LGBL of the MALT accounted for 83 cases. The diagnosis was based on (a) a characteristic cytology, which included centrocytoid cells, a varying degree of plasma cell differentiation, and some blasts; (b) the presence of lymphoepithelial lesions; and (c) the occurrence of two types of follicles easily detectable with Ki-FDC1p. Some were restricted to the mucosa, contained normal germinal center cells, and were indistinguishable from reactive follicles. Others consisted of small clusters of FDCs, were randomly distributed throughout the tumor, and escaped detection in conventional stainings. Such small clusters of FDCs were found to be restricted to LGBL of the MALT, not occurring in other types of LGBL, and were interpreted as tumor-associated abortive follicles discernable from residues of reactive follicles due to their cellular constituents, localization, and distribution pattern. Eight cases showed closed sheets of blasts and were classified as high grade malignant lymphoma secondary to LGBL of the MALT. In two cases the LGBL of the MALT were restricted to the mucosa, in 31 cases the submucosa was also infiltrated, and in the remaining 50 cases the infiltration also involved deeper wall layers of the GIT.(ABSTRACT TRUNCATED AT 250 WORDS)     

Recent advances in the study of dendritic cells and follicular dendritic cells

The role of dendritic cells in the initiation of immune responses, and of follicular dendritic cells in the presentation of antigen to B cells, is fundamental to our understanding of the immune system. A recent symposium* was convened in order to review progress in the study of the pathophysiology of these two cell types.     

Differential diagnosis of B-cell lymphoma rich in T cells and peripheral T-cell lymphomas

Clinicomorphological analysis of T-cell-rich B-cell lymphoma in a 50-year-old female and literature data revealed objective difficulties in morphological diagnosis using cytological and histological methods. Large number of epithelioid histiocytes and tumor cells polymorphism resembled Lennert's lymphoma (peripheral T-cell lymphoma). Immunohistochemical study confirmed B-cell origin of tumor cells and large number of reactive T-cells. It is suggested that it would be more correctly to use the term "Lennert-like areas" in such cases with subsequent immunohistochemical study.     

小B细胞恶性淋巴瘤形态学和免疫组织化学研究

目的：探讨各种小B细胞恶性淋巴瘤的形态学、免疫表型特征及其鉴别诊断。方法：对15例小淋巴细胞性淋巴瘤（SLL）、3例淋巴浆细胞性淋巴瘤（LPL）、36例滤泡性淋巴瘤（FL）、25例套细胞淋巴瘤（MCL）、7例淋巴结边缘区B细胞淋巴瘤（MZL）和30例黏膜相关淋巴细胞型结外边缘区B细胞淋巴瘤（MALT－MZL）的石蜡切片进行HE形态学观察和CD5、CD10、CD23和cyclinD1等抗体的免疫组织化学分析。结果：各种小B细胞恶性淋巴瘤在组成细胞和组织结构上各具特征；免疫表型：SLL表达CD5（82％）和CD23（80％），FL表达CD10（87％），MCL表达cyclinD1（84％）和CD5（80％），MZL／MALT－MZL和LPL均不表达CD5、CD10、CD23和cyclinD1。结论：各种小B细胞恶性淋巴瘤均是独立疾病，各具形态学和免疫表型特征，结合HE形态学观察和CD5、CD10、CD23、cyclinD1等免疫组化分析有助于正确诊断和鉴别诊断。     

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.     

Molecular and immunohistochemical characterization of B-cell lymphoma-2-negative follicular lymphomas

Aberrant expression of the antiapoptotic protein BCL (B-cell lymphoma)-2 in neoplastic germinal centers is one of the diagnostic hallmarks of follicular lymphoma. If BCL-2 cannot be detected by immunohistochemistry, the distinction between florid follicular hyperplasia and follicular lymphoma might become a diagnostic challenge. Most of those cases also lack the typical t(14;18), and the underlying pathophysiologic conditions of follicular lymphoma that lack BCL-2 protein expression are largely unknown. Here, we collected 18 BCL-2-negative follicular lymphoma cases from 5 different institutions. After restaining, 9 cases proved to be truly BCL-2 negative (6 follicular lymphoma grade 2, 2 follicular lymphoma grade 3a, and 1 follicular lymphoma grade 3b). In 4 additional cases, BCL-2 was very faint (all grade 2). Of the 9 BCL-2-negative follicular lymphoma cases, 2 were negative for CD10 (22%); all showed expression of BCL-6. Apoptotic level as determined by caspase 3 was the lowest in the BCL-2-positive follicular lymphoma group (15 ± 8 mm(2)), the highest in the normal/reactive group (n = 7, 60 ± 12 mm(2)) and very similar in the BCL-2 low follicular lymphoma and BCL-2-negative follicular lymphoma groups (25 ± 13 and 33 ± 19 mm(2), respectively), assuming an intermediate position between reactive follicles and BCL-2-positive neoplastic follicles (P < .001 [Kruskal-Wallis]). Also noted was a difference in proliferation fractions between the BCL-2-positive follicular lymphoma (27% ± 15%), the BCL-2 low follicular lymphoma (30% ± 20%) and the BCL-2-negative follicular lymphoma groups (30% ± 22%). Regarding the network of follicular dendritic cells, 8 (89%) of 9 cases from the BCL-2-negative subgroup showed disrupted, weakly developed networks, whereas all of the follicular lymphoma BCL-2 low-expression cases showed a well-defined and strongly developed follicular dendritic cell network. Among BCL-2-negative follicular lymphoma, BCL-2 and BCL-6 breaks were found in 1 case each, whereas in the follicular lymphoma BCL-2 low group, only 1 case with a BCL-6 break was recorded. No statistically significant result was achieved upon assessment of BCL-2α or BCL-2β RNA or the ratio of α/β isolated by real-time-polymerase chain reaction. Taken together, BCL-2-negative follicular lymphoma did not show a BCL-2 break on the genetic level and showed both increased apoptotic and proliferation rates compared with BCL-2-positive follicular lymphoma. In our series, BCL-6 breaks were infrequent in BCL-2-negative follicular lymphoma.     

Assessment of CD10 in the diagnosis of small B-cell lymphomas: a multiparameter flow cytometric study

We evaluated the usefulness of multiparameter flow cytometry with cluster analysis in the diagnosis of a series of 100 well-characterized small B-cell lymphomas (SBCLs). The histologic diagnoses in the 100 cases were follicular lymphoma (FL) in 58, marginal zone lymphoma (MZL) in 17, small lymphocytic lymphoma in 15, and mantle cell lymphoma (MCL) in 10. Of the 58 FLs, 57 were CD10 positive (98% sensitivity). The 1 negative case was unusual in that it occurred in the small intestine. However; architectural, cytologic, and immunohistochemicalfeatures were diagnostic of FL. Of 42 other SBCLs, 2 were CD10+ (95% specificity); 1 was a CD5+/cyclin D1 + MCL, and the other was an extranodal MZL. We found that assessment of CD10 expression using multiparameter flow cytometry with cluster analysis is highly sensitive and specific for the diagnosis of FL, validating its usefulness in situations in which adequate tissue is not available for definitive histologic diagnosis.     

Immunohistochemical analysis of human MHC class II antigens in B-cell non-Hodgkin's lymphomas

Twenty cases of B-cell non-Hodgkin's lymphoma (NHL) were evaluated by immunohistochemical staining of frozen sections with a panel of anti MHC class II monoclonal antibodies (MCA). These studies showed marked differences in the expression of class II antigens both between different cases and within the population of cells of individual cases. In all of the cases studied the majority of the tumour cells reacted with MCAs directed against determinants common to the products of SB and DR loci. However, MCAs specific for DC determinants failed to react with 3/20 cases and in several other cases stained only a minority of cells. Absent or reduced expression of DC antigens was most marked in lymphocytic lymphoma; however, in centroblastic-centrocytic and centroblastic lymphomas, DC antigens could be detected on the majority of cells.     

Usefulness of follicular dendritic cell pattern in classification of peripheral T-cell lymphomas

Classification of peripheral T-cell lymphomas based on morphological criteria can present problems due to overlap in histological features amongst the subtypes. An immunohistochemical study was designed to study the follicular dendritic cell patterns in 21 cases of peripheral T-cell lymphoma which had been classified using the updated Kiel classification. Three patterns of distribution were observed: 1 follicular dendritic cells not detected (3 cases); 2 follicular dendritic cells restricted to remnant follicle centres (7); 3 follicular dendritic cells present as an expanded network of cells exceeding the confines of germinal centres (11). Ten out of 11 angioimmunoblastic lymphomas showed an expanded network of follicular dendritic cells. The only negative case showed features which, on review, were in keeping with a pleomorphic, medium and large cell lymphoma showing an unusual proliferation of small venules. Other than angioimmunoblastic lymphomas, only one other case showed follicular dendritic cell hyperplasia. This was an unclassified peripheral T-cell lymphoma. We conclude that follicular dendritic cell hyperplasia may be used an an aid to diagnosis of the angioimmunoblastic type of peripheral T-cell lymphoma, and we recommend the routine staining of these cells in typing of T-cell lymphomas to facilitate comparison between centres.     

Dendritic reticulum cell-related immunostaining for laminin in follicular and diffuse B-cell lymphomas

Summary We performed a comparative immunohisto-cytochemical study of the distribution patterns of laminin and follicular dendritic reticulum cells (DRCs) within their follicular microenvironment in both nodular or diffuse B-cell non Hodgkin's lymphomas (NHLs). Twenty nine cases of immunophenotypically diagnosed B-cell NHLs (19 of follicular center cell origin-FCCL- and 10 of the diffuse well differentiated lymphocytic type-WDLL-) and five reactive lymph nodes with follicular hyperplasia were analyzed by immunoperoxidase and immunofluorescence techniques. Serial frozen sections and cytospin preparations were tested either with single antibodies anti laminin and DRC-1, or paired reagents in double labeling immunofluorescence. Our results indicated consistently that within both the reactive germinal centers and the neoplastic nodules of FCCL laminin immunostaining visualized a punctate-granular pattern apart from the linear vascular basement membrane positivity. Double immunofluorescence assay demonstrated that there was a close parallelism between this laminin staining pattern and DRC-1 distribution showing a well developed DRCs meshwork; in the diffuse tumour areas of both FCCL and WDLL, laminin immunoreactivity was found only in those cases in which nests of DRCs were observed. Double immunofluorescence studies performed on cytospin preparations demonstrated that the groups of cells containing DRC-1 positive cells, contained a positivity for laminin, although within the cell the staining for DRC-1 was intense and diffuse, while that for laminin was granular and more sparse. Our results suggested that these laminin and DRC-1 positive reactive sites may be present on the same cells. Since the reduction in number or loss of both DRCs and their related immunostaining for laminin within the microenvironment was consistently associated with a loss of nodularity by lymphoma cells, whereas nodularity in reactive and neoplastic conditions was associated with a rich DRCs meshwork and the related laminin immunostaining, a trapping function of DRCs exercised in the presence of laminin should be considered.This work was supported in part by a Grant N 87.02799.44 from the Consiglio Nazionale delle Ricerche, Progetto Finalizzato Oncologia, Rome, and by the Associazione Italiana per la Ricerca sul Cancro, Milan, Italy