Jo Spencer

Malignant lymphoma of mucosa‐associated lymphoid tissue

Lymphomas of the gastrointestinal tract, salivary glands, lung and thyroid are grouped together as tumours arising in mucosa‐associated lymphoid tissue. The great majority of them are of B‐cell origin but distinctive T‐cell lymphomas are also recognized in the gastrointestinal tract. These lymphomas tend to remain localized for prolonged periods but, whereas the B‐cell group respond favourably to local therapy, the T‐cell group are associated with severe morbidity and their overall prognosis is extremely poor. Accepted histological classifications of non‐Hodgkins lymphomas are difficult to apply to these tumours. In this paper their morphological features are reviewed; recent findings based on immunohistochemistry and DNA analysis are presented; and the biological behaviour of these tumours is discussed insofar as they offer insight into mucosal immunological mechanisms.

The response of cells from low-grade B-cell gastric lymphomas of mucosa-associated lymphoid tissue to Helicobacter pylori.

An association has been shown between colonisation of gastric mucosa by Helicobacter pylori, acquisition of mucosa-associated lymphoid tissue (MALT), and occurrence of primary B-cell gastric MALT lymphoma. We investigated the immunological response of cells from 3 low-grade primary B-cell gastric MALT lymphomas to H pylori type NCTC 11637 and 12 isolates of H pylori from patients without lymphomas. After co-culture of tumour cells with bacteria, cells were examined for phenotypic evidence of activation and proliferation, and supernatant assayed to detect tumour-derived immunoglobulin and interleukin-2 (IL-2). Neoplastic B cells and non-neoplastic T cells proliferated, and IL-2-receptor expression by most cells in the cultures was increased with stimulating strains of H pylori. There were also increases in tumour immunoglobulin and IL-2 release when activation and proliferation were seen in response to stimulating bacteria. Removal of T cells from the tumour cell suspension reduced proliferation and IL-2-receptor expression. In comparison, no responses were seen in cells from high-grade gastric MALT lymphomas or low-grade B-cell MALT lymphomas of other sites. The response of low-grade B-cell gastric MALT lymphomas to stimulating strains of H pylori is dependent on H-pylori-specific T cells and their products, rather than the bacteria themselves.

HELICOBACTER PYLORI‐SPECIFIC TUMOUR‐INFILTRATING T CELLS PROVIDE CONTACT DEPENDENT HELP FOR THE GROWTH OF MALIGNANT B CELLS IN LOW‐GRADE GASTRIC LYMPHOMA OF MUCOSA‐ASSOCIATED LYMPHOID TISSUE

Previous studies have shown that tumour cells from low‐grade B‐cell gastric lymphomas of mucosa‐associated lymphoid tissue (MALT) type proliferate in vitro in response to heat‐killed whole cell preparations of Helicobacter pylori, but only in the presence of tumour‐infiltrating T cells. This response is strain‐specific in that the tumours studied responded optimally to different strains of H. pylori. It was unclear from these studies, however, whether the ability to recognize the specific stimulating strains of H. pylori was a property of the tumour cells or the tumour‐infiltrating T cells. This study shows that whereas the tumour cells do not respond to H. pylori, both freshly isolated tumour‐infiltrating T cells and a T cell line derived from these cells proliferate in response to stimulating strains of H. pylori. T cells from the spleen of one of the patients do not share this property. These results suggest that B‐cell proliferation in cases of low‐grade gastric lymphoma of MALT type in vitro in response to H. pylori is due to recognition of H. pylori by tumour‐infiltrating T cells, which in turn provide help for tumour cell proliferation. The observations provide an explanation for properties of gastric MALT‐type lymphoma, such as regression following eradication of H. pylori and the tendency of the tumour to remain localized to the primary site.

MALIGNANT HISTIOCYTOSIS OF THE INTESTINE: A T-CELL LYMPHOMA

Malignant lymphoma complicating coeliac disease has been characterised on morphological and immunocytochemical grounds as malignant histiocytosis of the intestine (MHI). Fresh tissue from four cases of MHI was studied by means of a panel of monoclonal antibodies; in three cases tumour DNA was studied for immunoglobulin and T-cell receptor (TCR) gene rearrangement. Immunocytochemistry showed a T-cell phenotype in all four cases, confirmed by the demonstration of a rearranged TCR beta-chain gene in the three cases studied. Lymphoma complicating coeliac disease thus appears to be of T-cell, rather than histiocyte, origin.

Ectopic Lymphoid Structures Support Ongoing Production of Class-Switched Autoantibodies in Rheumatoid Synovium

Background Follicular structures resembling germinal centres (GCs) that are characterized by follicular dendritic cell (FDC) networks have long been recognized in chronically inflamed tissues in autoimmune diseases, including the synovium of rheumatoid arthritis (RA). However, it is debated whether these ectopic structures promote autoimmunity and chronic inflammation driving the production of pathogenic autoantibodies. Anti-citrullinated protein/peptide antibodies (ACPA) are highly specific markers of RA, predict a poor prognosis, and have been suggested to be pathogenic. Therefore, the main study objectives were to determine whether ectopic lymphoid structures in RA synovium: (i) express activation-induced cytidine deaminase (AID), the enzyme required for somatic hypermutation and class-switch recombination (CSR) of Ig genes; (ii) support ongoing CSR and ACPA production; and (iii) remain functional in a RA/severe combined immunodeficiency (SCID) chimera model devoid of new immune cell influx into the synovium. Methods and Findings Using immunohistochemistry (IHC) and quantitative Taqman real-time PCR (QT-PCR) in synovial tissue from 55 patients with RA, we demonstrated that FDC+ structures invariably expressed AID with a distribution resembling secondary lymphoid organs. Further, AID+/CD21+ follicular structures were surrounded by ACPA+/CD138+ plasma cells, as demonstrated by immune reactivity to citrullinated fibrinogen. Moreover, we identified a novel subset of synovial AID+/CD20+ B cells outside GCs resembling interfollicular large B cells. In order to gain direct functional evidence that AID+ structures support CSR and in situ manufacturing of class-switched ACPA, 34 SCID mice were transplanted with RA synovium and humanely killed at 4 wk for harvesting of transplants and sera. Persistent expression of AID and Iγ-Cμ circular transcripts (identifying ongoing IgM-IgG class-switching) was observed in synovial grafts expressing FDCs/CD21L. Furthermore, synovial mRNA levels of AID were closely associated with circulating human IgG ACPA in mouse sera. Finally, the survival and proliferation of functional B cell niches was associated with persistent overexpression of genes regulating ectopic lymphoneogenesis. Conclusions Our demonstration that FDC+ follicular units invariably express AID and are surrounded by ACPA-producing plasma cells provides strong evidence that ectopic lymphoid structures in the RA synovium are functional and support autoantibody production. This concept is further confirmed by evidence of sustained AID expression, B cell proliferation, ongoing CSR, and production of human IgG ACPA from GC+ synovial tissue transplanted into SCID mice, independently of new B cell influx from the systemic circulation. These data identify AID as a potential therapeutic target in RA and suggest that survival of functional synovial B cell niches may profoundly influence chronic inflammation, autoimmunity, and response to B cell–depleting therapies.

Activation-induced cytidine deaminase expression in follicular dendritic cell networks and interfollicular large B cells supports functionality of ectopic lymphoid neogenesis in autoimmune sialoadenitis and MALT lymphoma in Sjögren's syndrome

Demonstration of ectopic germinal center-like structures (GC-LSs) in chronically inflamed tissues in patients with autoimmune disorders is a relatively common finding. However, to what extent ectopic lymphoid structures behave as true GC and are able to support class switch recombination (CSR) and somatic hypermutation (SHM) of the Ig genes is still debated. In addition, no information is available on whether CSR and SHM can take place in the absence of GCs at extrafollicular sites in an ectopic lymphoid tissue. In this study, we show that in salivary glands (SGs) of Sjögren’s syndrome (SS) activation-induced cytidine deaminase (AID), the enzyme responsible for CSR and SHM is invariably expressed within follicular dendritic cell (FDC) networks but is not detectable in SGs in the absence of ectopic GC-LSs, suggesting that FDC networks play an essential role in sustaining the Ag-driven B cell proliferation within SS-SGs. We also show that the recently described population of interfollicular large B cells selectively expresses AID outside ectopic GC in the T cell-rich areas of periductal aggregates. Finally, we report that AID retains its exclusive association with numerous, residual GCs in parotid SS-MALT lymphomas, whereas neoplastic marginal zone-like B cells are consistently AID negative. These results strongly support the notion that ectopic lymphoid structures in SS-SGs express the molecular machinery to support local autoantibody production and B cell expansion and may play a crucial role toward lymphomagenesis.

Human Peyer's patches: an immunohistochemical study

We have used immunoperoxidase techniques to characterise the Peyers patches in human terminal ileum. The mantle zones of the B cell follicles in human Peyers patches were surrounded by B cells which did not express surface IgD but which mostly expressed surface immunoglobulin of the IgM and/or IgA1 isotype. Few cells expressing surface IgG or IgA2 were detected. Cells with cytoplasmic immunoglobulin of all isotypes except IgD were present in the dome regions of the Peyers patches as well as in the lamina propria. There was little evidence of traffic of immunoglobulin synthesising cells across the high endothelial venules. T cells were seen to surround the lymphoid follicles. They were most concentrated on the serosal aspect around the high endothelial venules. Cells with macrophage-like morphology were present in both the lamina propria and the dome region of the follicles; those in the lamina propria containing lysozyme and those in the dome region S100 protein. The results are discussed in relation to the generation and dissemination of antibody producing cells in human gut.

CXCL13, CCL21, and CXCL12 expression in salivary glands of patients with Sjogren's syndrome and MALT lymphoma: Association with reactive and malignant areas of lymphoid organization

The chemokines (CKs) CXCL13, CCL21, and CXCL12 are known to play differential roles in the organization of the lymphoid tissues and the development of lymphoid malignancies. We investigated the expression of these CKs and their receptors in the salivary glands of Sjogren’s syndrome patients with lymphoepithelial lesions (lymphoepithelial sialadenitis or LESA) and in MALT lymphoma to understand their involvement in salivary gland lymphomagenesis. We demonstrate that within salivary glands with LESA and MALT lymphoma the lymphoid CKs CXCL13 and CCL21 are selectively associated with areas of reactive lymphoid proliferation, whereas no significant expression of these molecules was detected in the malignant lymphoid aggregate. Conversely, CXCL12 was observed predominantly in infiltrated ducts and malignant B cells. Accordingly, CXCL13 and CCL21 transcript levels were significantly increased in LESA samples while CXCL12 levels were increased in MALT lymphoma and isolated tumor cells. Low levels of CK receptors were detected on lymphoma-extracted lymphocytes, suggesting down-regulation in the abundance of ligands. Our findings suggest that in salivary gland MALT lymphoma the lymphoid CKs CXCL13 and CCL21 are directly implicated in the organization of ectopic reactive lymphoid tissue, whereas CXCL12 is associated with the infiltrated epithelium and malignant B cell component and is possibly involved in the regulation of malignant B cell survival.

Gamma/delta T cells and the diagnosis of coeliac disease

Gamma/delta T cells are increased in the gut epithelium of patients with coeliac disease compared with normal controls. The aim of this study was to determine whether the increase in yd intraepithelial lymphocytes (IEL) is specific for coeliac disease, in which case it could be of diagnostic importance. Biopsies were obtained from children with no intestinal disease, coeliac disease, cow‐milk‐sensitive enteropathy/post‐enteritis syndrome (CMSE/PES) and miscellaneous other enteropathies (n = 67). Intraepithelial CD3+ and γδ T cells were identified in frozen sections using peroxidase immunohisto‐chemistry. In normal biopsies there were 0‐7 γδ IEL/100 cells in the epithelium. In untreated coeliac patients this increased to 9‐22 γδ IEL/100 cells in the epithelium (P=0.000004). Of 27 patients with morphologic intestinal damage which was not due to coeliac disease, four with CMSE/PES had γδ IEL/100 cells in the epithelium in the same range as the patients with coeliac disease. Of these, two had high densities of CD3+ IEL in the epithelium and were indistinguishable from patients with untreated coeliac disease. The other two could be excluded as possible coeliacs because their CD3f IEL/100 epithelial cells were in the normal range. Thus an increase in γδ IEL is not specific for coeliac disease. However, enumeration of both of γδ IEL and CD3+ IEL densities will be useful in the exclusion of coeliac disease as a diagnosis in some children.

Mouse and human intestinal immunity: same ballpark, different players; different rules, same score

The study of animal immune physiology and animal models of human disease have accelerated many aspects of translational research by allowing direct, definitive investigations. In particular, the use of mice has allowed genetic manipulation, adoptive transfer, immunization, and focused cell and tissue sampling, which would obviously be unthinkable for studies in humans. However, the disease relevance of some animal models may be uncertain and difficulties in interpretation may occur as a consequence of immunological differences between the two species. In this review, we will consider general differences in the structure and development of human and mouse mucosal lymphoid microenvironments and then discuss species differences in mucosal B- and T-cell biology that relate to the current concepts of intestinal immune function.