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).