γδ T cells cluster in B-cell follicles within secondary lymphoid tissues. Immunohistochemical analysis of tissue section from human biopsy specimen by means of bright field (A-C) and fluorescence microscopy (D-E). (A) Normal abdominal LN, (B) gut follicle from a patient with ileitis (Yersinia), and (C) draining LN from a patient with appendicitis (Yersinia). Red staining in panels A-C depicts positivity for γδ T cells using a goat Ab against pan-VγVδ-TCR or BCA-1 and SLC as indicated using mouse mAb, and IgG refers to negative control staining with isotype-matched unrelated Ab. (D-E) Assessment of γδ T-cell distribution in sections of an abdominal LN from a patient with yersiniosis. Double-fluorescence images show localization of γδ T cells in green, CD3⁺ T cells (D) and CD21⁺ FDCs (E) in red, and the corresponding superimposed images (overlays).