Secondary Lymphoid Tissues ›› Lymph Node ›› Normal Normal Lymph Node* Click Here for Full Size › Microscopic Features: An encapsulated lymphoid tissue (as opposed to Mucosa Associated Lymphoid Tissue, also known as MALT) Comprised of follicles (primary and secondary) and interfollicular areas B-cells mostly reside in the follicles while T-cells mostly reside in between the follicles (interfollicular areas) Most of the follicles are located within the cortex › Normal % blood-PB, marrow-BM, lymphoid tissue-LN: PB: N/A BM: N/A LN: N/A › May Resemble: Non-neoplastic Lymphadenitis Follicular Lymphoma › Differential Diagnoses: Reactive lymphoid hyperplasia Infectious Lymphadenitis Follicular Lymphoma › Classic Immunophenotype: "T"-cells have the "Tiny" CDs: CD2, CD3, CD4, CD5, CD7, CD8 "B"-cells have the "Bigger" CDs: CD19, CD20, CD22 › Cartoon Image: › Misc: In a normal lymph, the primary follicles (not antigen stimulated and no germinal center) and secondary follicles (antigen stimulated with a germinal center) are where most B-cell reside The interfollicular (between follicles) areas are where most T-cells reside In summary: B-cells mostly reside in the follicles while T-cells mostly reside in between the follicles (interfollicular areas)