Falini B, Fizzotti M, Pileri S, Liso A, Pasqualucci L, Flenghi L
Institute of Hematology, University of Perugia, Italy.
Ann Oncol. 1997;8 Suppl 2:101-4.
The human bcl-6 gene, which is rearranged in about 30% of diffuse large B-cell lymphomas (DLCL-B), encodes for a Kruppel-type zinc finger protein of 706 amino acids. In order to investigate the expression of the bcl-6 gene at the protein level, two monoclonal antibodies (PG-B6a and PG-B6p) directed against the human bcl-6 protein were generated by immunizing Balb/c mice with a recombinant protein corresponding to the amino-terminal region (amino acids 3-484) of bcl-6. PG-B6a (a = avian) recognized the most conserved bcl-6 epitope (expressed in many animal species, including avian). PG-B6p (p = paraffin) reacted with an epitope of bcl-6 partially resistant to fixatives and detectable on microwave-heated paraffin sections. At immunocytochemistry, bcl-6 localized in the nucleus with a microgranular or diffuse pattern. Strong nuclear expression of bcl-6 was mainly detected in normal germinal-center B-cells, whereas mantle- and marginal-zone B cells, as well as plasma cells and marrow B-cell precursors, did not express bcl-6. These immunohistological findings strongly suggest that bcl-6 may play a role as a regulator of germinal-center related functions. All MoAbs stained neoplastic cells of follicular lymphomas, DLCL-B, and Burkitt's lymphomas. In DLCL-B, bcl-6 expression was independent of bcl-6 gene rearrangements and did not correlate with expression of other markers or the proliferation index. Among low-grade B-cell lymphomas, immunostaining for bcl-6 proved useful for differentiating proliferation centers in B-CLL (bcl-2+/bcl-6-) from trapped germinal centers in mantle-cell lymphomas (bcl-2-/bcl-6+). Strong nuclear positivity for bcl-6 was consistently detected in tumor (L&H) cells of nodular, lymphocyte-predominant Hodgkin's disease (NLPHD). These results further support the concept that NLPHD is a histogenetically distinct (germinal-center derived) subtype of HD. Notably, the nuclei of reactive CD3+/ CD4+ T cells near to and rosetting around L&H cells in NLPHD were also strongly bcl-6+, but lacked CD40 ligand (CD40L) expression. This staining pattern clearly differed from that of classic HD, whose cellular background was made up of CD3+/CD4+ T cells showing the bcl-6-/CD40L+ phenotype. The above immunohistological findings suggest that (a) bcl-6 may play a role in regulating B-cell differentiation step(s) occurring within germinal centers; (b) deregulated bcl-6 expression caused by rearrangements may contribute to B-lymphomagenesis; (c) bcl-6 is possibly involved in the pathogenesis of NLPHD.
人类bcl-6基因在约30%的弥漫性大B细胞淋巴瘤（DLCL-B）中发生重排，编码一种由706个氨基酸组成的Kruppel型锌指蛋白。为了研究bcl-6基因在蛋白质水平的表达，通过用对应于bcl-6氨基末端区域（氨基酸3 - 484）的重组蛋白免疫Balb/c小鼠，产生了两种针对人类bcl-6蛋白的单克隆抗体（PG-B6a和PG-B6p）。PG-B6a（a = 禽类）识别最保守的bcl-6表位（在包括禽类在内的许多动物物种中表达）。PG-B6p（p = 石蜡）与bcl-6的一个部分抗固定剂且在微波加热的石蜡切片上可检测到的表位反应。在免疫细胞化学中，bcl-6定位于细胞核，呈微粒状或弥漫状分布。bcl-6的强核表达主要在正常生发中心B细胞中检测到，而套细胞和边缘区B细胞以及浆细胞和骨髓B细胞前体不表达bcl-6。这些免疫组织学结果强烈提示bcl-6可能作为生发中心相关功能的调节因子发挥作用。所有单克隆抗体均能染色滤泡性淋巴瘤、DLCL-B和伯基特淋巴瘤的肿瘤细胞。在DLCL-B中，bcl-6表达与bcl-6基因重排无关，且与其他标志物的表达或增殖指数无关。在低级B细胞淋巴瘤中，bcl-6免疫染色有助于区分B-CLL中的增殖中心（bcl-2+/bcl-6-）和套细胞淋巴瘤中的被困生发中心（bcl-2-/bcl-6+）。在结节性淋巴细胞为主型霍奇金病（NLPHD）的肿瘤（L&H）细胞中始终检测到bcl-6强核阳性。这些结果进一步支持了NLPHD是HD组织发生学上不同（生发中心来源）亚型的概念。值得注意的是，NLPHD中靠近L&H细胞并与其形成花环的反应性CD3+/CD4+ T细胞的细胞核也强烈bcl-6阳性，但缺乏CD40配体（CD40L）表达。这种染色模式与经典HD明显不同，经典HD的细胞背景由表现为bcl-6-/CD40L+表型的CD3+/CD4+ T细胞组成。上述免疫组织学结果提示：（a）bcl-6可能在调节生发中心内发生的B细胞分化步骤中起作用；（b）重排导致的bcl-6表达失调可能促成B淋巴细胞瘤的发生；（c）bcl-6可能参与NLPHD的发病机制。
