BCA-1 is highly expressed in Helicobacter pylori–induced mucosa-associated lymphoid tissue and gastric lymphoma (original) (raw)
Specimen histopathology. Chronic antrum inflammation with lymphoid follicles was observed in all samples of Hp gastritis. The bacteria were detected at the mucosal surface in all cases by hematoxylin and eosin or modified Giemsa staining. Infiltration by neutrophils was moderate to marked. NSAID-induced chronic gastritis had a characteristic appearance, with occasional mucosal erosions. The samples of NSAID-induced gastritis and normal gastric mucosa were all Hp-negative, both by histology and by the urease test. Samples from 10 patients with gastric lymphoma were studied. In 5 cases, high-grade lymphoma was diagnosed by the presence of sheets of transformed blasts. The other 5 cases were diagnosed as low-grade. In 4 of the 5 low-grade lymphomas, the tumor was confined to the mucosa and submucosa, whereas all high-grade lymphomas showed infiltration of the whole stomach wall. In all instances, Hp infection was confirmed histologically and chronic gastritis with lymphoid hyperplasia was observed in the vicinity of the neoplastic tissue.
Hp and NSAID gastritis. Marked BCA-1 expression was found in all samples of Hp gastritis. Expression was mainly confined to lymphocyte aggregates and to primary and secondary follicles. BCA-1 transcripts were evenly distributed in nonorganized B lymphocyte aggregates but were restricted to the mantle zone in secondary lymphoid follicles. An intermediate arrangement was also observed, which presumably reflects the process of organization of the aggregates into lymphoid follicles (Figure 1). The degree of BCA-1 expression as assessed by the hybridization signals was not related to the number of bacteria detected at the mucosal surface, or to the presence of infiltrating neutrophils and eosinophils in the lamina propria. The distribution of BCA-1–producing cells in Hp-induced gastric MALT is similar to that observed in normal lymphoid tissues, as shown in Figure 1. BCA-1 transcripts were not detected in endothelial cells or in the epithelial cells of the mucosa, even in the vicinity of colonizing bacteria. Occasional BCA-1–expressing cells (accounting for less than 0.5% of the total as determined by image analysis) were found outside the MALT in the lamina propria of the antrum and the corpus in Hp- and NSAID-induced gastritis, but were also in control specimens. The significance of this rare expression, which is not related to Hp infection, is unknown.
In situ expression of BCA-1 in chronic Hp gastritis. Expression is observed in the whole area of lymphoid aggregates (a) and is restricted to the mantle zone in secondary lymphoid follicles (c). Intermediate distribution (b) is found occasionally. (d–f) Localization of follicular dendritic cells as detected in serial sections by immunohistochemical staining for CD21. Bottom: In situ expression of BCA-1 in a secondary follicle of a normal lymph node. Antisense and sense hybridization is shown. ×100 (original magnification).
To identify the cells that produce BCA-1, we analyzed serial sections of several secondary gastric MALT follicles by immunohistochemistry. As shown in Figures 1 and 2, BCA-1 transcripts were found in areas containing many follicular dendritic cells as evidenced by immunoreactivity for CD21, and in areas where B lymphocytes accumulate. The data obtained on examination of nearly 50 MALT follicles in serial sections were consistent with those presented in Figure 2. T lymphocytes (CD3+), macrophages (CD68+), endothelial cells (CD31+), and CD1a+ dendritic cells were also present in the MALT, but their distribution differed markedly from that of cells expressing BCA-1 (data not shown). Immunohistochemical studies were carried out to assess the expression of the BCA-1 and CXCR5 proteins. As shown in Figure 2, BCA-1 was confined mainly to the mantle zone of lymphoid follicles. The reticular appearance of the staining is consistent with BCA-1 production by follicular dendritic cells. CXCR5 was expressed by lymphocytes of the mantle zone and by occasional centroblast-like cells within the germinal centers (Figure 2). BCA-1 staining was also analyzed in human tonsils using frozen sections to avoid possible artifacts from formalin fixation. In these preparations, intense staining was observed not only in the dendritic cells, but also in the lymphocytes of the mantle zone. Lymphocyte BCA-1 reactivity may indicate that the chemokine is produced by B lymphocytes, or may simply reflect its binding to CXCR5.
BCA-1 and CXCR5 expression in chronic Hp gastritis. (a) In situ expression of BCA-1 is shown in the mantle zone of a secondary lymphoid follicle. The sense probe control (b) and staining for B lymphocytes (CD20+) (c) are shown in serial sections of the same follicle. ×100 (original magnification). BCA-1 (d) and CXCR5 (f) immunostaining is shown with the corresponding isotype-matched controls (e and g). Staining of a frozen section of a tonsil (h) and control (i) shows BCA-1 in association with small round and stellate cells, suggesting expression by lymphocytes and dendritic cells. ×200 (original magnification).
Gastric MALT lymphomas. In view of the seemingly prominent role of BCA-1 in chronic Hp gastritis, we also analyzed the expression of this chemokine in the MALT lymphomas that may develop as the disease progresses. Prominent BCA-1 expression assessed at the mRNA and protein level was found in the neoplastic tissue, which was devoid of follicular dendritic cells, as indicated by the lack of immunostaining with antibodies directed against CD21 and CD23 (data not shown). In both stages, BCA-1 appears to be expressed and produced predominantly by the neoplastic cells. In Figure 3, BCA-1 expression is clearly visible in a low-grade lymphoma that contrasts with the adjacent mucosa, where no expression was found. Evenly distributed BCA-1 expression is found in high-grade lymphomas, where the transformed blasts were the major source of the chemokine (Figure 3). Intensity of expression varied somewhat among the blasts; numerous small mononuclear cells within the tumor tissue were negative. The expression of CXCR5 was even more pronounced and was evenly distributed, suggesting that the BCA-1 receptor is present in transformed B cells as well as in the infiltrating lymphocytes.
Expression of BCA-1 and CXCR5 in gastric MALT lymphomas. In situ expression of BCA-1 in (a) low-grade lymphoma with surrounding normal gastric mucosa, ×40 (original magnification); and in high-grade lymphoma (b and c), ×200 and ×400, respectively (original magnification). Immunostaining of BCA-1 and CXCR5 in high-grade lymphoma (d and e), ×400 and ×200, respectively (original magnification).
SLC expression in gastric MALT and lymphomas. The chemokine SLC is also known to attract B lymphocytes and to be involved in the development of nodal and extranodal lymphoid tissues (17–19). Previous studies of normal lymph nodes showed that SLC is present at the outer rim of follicles and in the interfollicular area (18). This distribution is in striking contrast with that found in the MALT of the Hp-infected gastric mucosa, where only occasional, scant expression of SLC is observed (Figure 4). SLC gene expression was regularly found in endothelial cells throughout the mucosa and the submucosa. However, no expression was detected in epithelial cells. In low- and high-grade lymphomas, as in the non-neoplastic gastric MALT, the expression of SLC and BCA-1 differ completely. Strong SLC positivity was found in endothelial cells lining the microvessels within the neoplastic tissue, but no expression was detected in the transformed B blasts (Figure 4).
In situ expression of SLC in chronic Hp gastritis (a) and in high-grade lymphoma (b). SLC expression is rare in Hp gastritis (arrows) and is confined to endothelial cells in the lymphoma. ×100 (original magnification).