Class II β-tubulin is a novel marker for human tonsillar M cells and follicular dendritic cells

Objective: Membranous (M) cell of the human palatine tonsil is an antigen entry site for mucosal infection, but its location is obscure in histological sections. Recently, a microarray analysis has demonstrated that clusterin, annexin A5, CD44, MMP14, and β-tubulin are candidate genes of M cell marker in mice. Among these genes, we here describe class II β-tubulin as a new marker for human tonsillar M cells and follicular dendritic cells (FDCs), and present its usefulness for diagnosis of angioimmunoblastic T-cell lymphomas (AILTs). Materials and methods: Immunohistochemistry and Western blotting for class II β-tubulin were performed using 81 cases of lymphoid, gastrointestinal and thyroid tissues, and an FDC cell line, respectively. Double immunostaining with clusterin and class II β-tubulin were carried out. Results: Class II β-tubulin localized the M cells and FDCs in the palatine tonsils (10/10, 100%) and adenoids (10/10, 100%). It was colocalized with clusterin in the palatine tonsils. However, class II β-tubulin staining did not identify intestinal M cells in the intestines. Immunoblot analysis revealed that class II β-tubulin expression was upregulated in HK cells, a normal FDC cell line. Class II β-tubulin immunostaining highlighted hyperplastic FDC meshworks in all AILTs (14/14, 100%). Conclusion: Class II β-tubulin is a specific histochemical marker for human tonsillar M cells and FDCs. Thus, class II β-tubulin immunostaining may be useful to identify tonsillar M cells and to diagnose FDC proliferative lesions such as AILT.