Image Description
Proliferation of follicular dendritic cells (FDC) outside residual follicles is a diagnostic hallmark of angioimmunoblastic T-cell lymphoma (AITL). The FDC meshworks are expanded and disorganized and surround or abut the high endothelial venules - another key histologic feature of AITL.
In some cases, the “burned-out” follicles are surrounded by multiple concentric layers of FDC creating an “onion-skin appearance.” The FDC meshwork can be highlighted by immunostains for CD21 (shown here), CD23, or CD35. The CD21+ cells may not be true FDC but activated fibroblastic reticulum cells with upregulation of CD21.
About the Disease
Angioimmunoblastic T-cell lymphoma (AITL) is a type of peripheral T-cell lymphoma arising from follicular helper T cells of the germinal center. It is a systemic disease that presents with generalized lymphadenopathy, hepatosplenomegaly, constitutional symptoms, skin rash, anemia, and polyclonal hypergammaglobulinemia. There is effacement of the normal nodal architecture with disappearance of follicles and germinal centers, a polymorphic cellular infiltrate that extends into perinodal tissues, and proliferation of high endothelial venules and follicular dendritic cells. The atypical T-cells have irregular nuclei and clear cytoplasm. Epstein-Barr virus (EBV) can be detected by in-situ hybridization in 80% to 90% of lymph nodes affected by AITL. The virus is present in transformed B-cells and is not considered to play a role in the pathogenesis. The T-cell receptor genes are clonally rearranged. AITL is a rapidly progressive disease with a median survival of under 3 years. Given the abnormal T-cell function and the immunodeficient state, the cause of death in most cases is complications from infectious diseases. Many patients with AITL also develop EBV+ diffuse large B-cell lymphoma. References:Jaffe, E. S. et al (2017). Hematopathology - Second Edition. Philadelphia, PA. Elsevier. Swerdlow S. H. et al (2017). WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues. Revised 4th Edition. Lyon, France.