I have found a note that I have made during a lymphoma talk at Sabah by Dr Ahmad Toha. Here is the gist of it. About Lymphoid Follicles There are two types of lymphoid follicles: one is primary and another is secondary lymphoid follicle. Primary lymphoid follicle: dark blue in colour, stain less with Ki-67 proliferative index marker. Secondary lymphoid follicle: has paler areas, stain more with Ki-67 proliferative index marker. Useful markers for lymph nodes: CD20: germinal centre and mantle cell. CD79a: stronger staining at the mantle zone. BCL-2: an anti-apoptotic marker, mostly stain outside the follicle with 'sprinkle' of positive cells inside the follicle. These positive cells inside the follicles are T-helper cells. CD21: identify the nodular appearance of the follicles. Ki-67 BCL-6: germinal centre CD10: germinal centre IgD: stain outside the germinal centre (?mantle zone) About Thymus: 1. Paracortex Densely cellular Located beneath cortex, at c...