Department of Anatomy, Histology and Embryology Semmelweis University, Budapest 1094, Hungary.
Ceva-Phylaxia Ltd, Budapest 1107, Hungary.
Poult Sci. 2022 Apr;101(4):101727. doi: 10.1016/j.psj.2022.101727. Epub 2022 Jan 13.
The bursal secretory dendritic cell (BSDC) was discovered more than 40 yr ago. It is a highly polarized, granulated cell, locating in the medulla of bursal follicle. The cytoplasmic granules either discharge or fuse together forming large, irregular-shaped, dense bodies. Formation of the dense bodies could be the first sign of BSDC transformation to macrophage-like cell (Mal) which is the result of terminal maturation of BSDC. The BSDC is non-phagocytic, unlike Mal. The discharged substance may be attached to the cell membrane (membrane-bound form) and after detaching, appears as a flocculated substance in the extracellular space of medulla. Movat pentachrome staining shows, that this substance is a glycoprotein (gp), which may be contributed to the microenvironment of the medulla. Medullary lymphocytes are floating in the gp. Precursors of the BSDC locate in the corticomedullary epithelial arches, which operate under the effect of Notch/Serrate signaling. The Notch signaling determines the fate of lymphoblast-like precursor cells and inhibits the appearance of immunoglobulin heavy chain. In the arches, the precursor cells proliferate and entering the medulla differentiate. The dense bodies pack the virus particles, which prevents the granular discharge, resulting in disappearance of extracellular gp, but gp emerges inside the virus containing Mal. In infected birds, the Mal contains either apoptotic cells or virus particles. If vaccination or infectious bursal disease virus (IBDV) infection use up the BSDC precursors, the recovery of follicle is critical.
囊状分泌树突状细胞（BSDC）是 40 多年前发现的。它是一种高度极化的颗粒细胞，位于囊状滤泡的髓质中。细胞质颗粒要么排出，要么融合在一起形成大的、不规则形状的致密体。致密体的形成可能是 BSDC 向巨噬样细胞（Mal）转化的第一个信号，这是 BSDC 终末成熟的结果。BSDC 是非吞噬的，不像 Mal。排出的物质可能附着在细胞膜上（膜结合形式），然后在脱离后，在外质的髓质空间中呈现为絮状物质。Movat 五重染色显示，这种物质是一种糖蛋白（gp），它可能对髓质的微环境有贡献。髓质中的淋巴细胞漂浮在 gp 中。BSDC 的前体细胞位于皮质-髓质上皮弓中，这些前体细胞在 Notch/Serrate 信号的作用下运作。Notch 信号决定淋巴母细胞样前体细胞的命运，并抑制免疫球蛋白重链的出现。在弓状结构中，前体细胞增殖并进入髓质分化。致密体包裹病毒颗粒，从而阻止颗粒的排出，导致细胞外 gp 的消失，但 gp 出现在含有 Mal 的病毒内部。在感染的鸟类中，Mal 中含有凋亡细胞或病毒颗粒。如果疫苗接种或传染性囊病病毒（IBDV）感染耗尽了 BSDC 前体，那么滤泡的恢复是至关重要的。
