Figure 1. Diagrammatic representation of reactive lymph node patterns.

Figure 2. Follicular hyperplasia. The histology shows the typical circumferential distribution of secondary follicles (arrow) beneath the capsule. Immunostains (red) show how B cells, T cells, proliferating cells and macrophages are distributed.

Figure 3. Sinus histiocytosis. Here the lymph node is expanded by enlarged sinuses (arrows in (a)) composed mainly of macrophages (c). The preserved B and T-cell areas are highlighted by immunostaining (brown) in (b) and (d), respectively.

Figure 4. Paracortical expansion. (a) shows a large expansion of the paracortical area between the follicles (arrows) composed of cells that are (b) CD1a-positive (shown as brown cells) indicating an accumulation of Langerhan's cells (dermatopathic lymphadenopathy).

Figure 5. (a) The paracortex is expanded between the follicles (arrows) by a mixed reaction containing many large blast cells (b) that are EBV (shown in (c)) positive B cells (shown in (d)) surrounded by a florid T-cell reaction (e). All immunostained cells are shown as brown. Cells are immunostained for the presence of EBV antigens in (c) using antibodies against the latent membrane protein of EBV, for the B-cell antigen CD20 in (d) and for the T-cell antigen CD3 in (e).

Figure 6. Tuberculosis replaces the lymph node structure particularly in the paracortex (a) with caseating granulomas (caseation shown by the black arrow in (a)) composed of epithelioid macrophages (brown cells in (c)) and multinucleate giant cells (white arrow in (b)). Tubercle bacilli can be identified by a special stain known as a Ziehl Nielsen (red bacteria in (d)).

Figure 7. In Castleman disease the lymph node is replaced by nodules with a superficial resemblance to secondary follicles (white arrows in (a) and (b)) in which the centre is not composed of lymphocytes but is replaced by a vascular proliferation (white arrows in (c) and (d)).