Dendritic cells in the bursal follicles and germinal centers of the chicken's caecal tonsil express vimentin but not desmin

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Abstract
Background: Immunohistochemical studies with anti‐vimentin and anti‐desmin monoclonal antibodies were designed to determine the origin of bursal secretory dendritic cells (SDC) and follicular dendritic cells. Methods: The binding sites of anti‐vimentin, anti‐desmin, and antichicken‐IgG specific monoclonal antibodies were visualized with a biotinylated anti‐mouse‐IgG, ABC Elite kit, and 4‐chloronaphthol. Cells were double stained (anti‐vimentin and rabbit anti‐chicken‐IgG Fc) to determine if the vimentin positive cells possessed surface IgG. Results: Vimentin positive cells were observed in the cortex and medulla of the bursa and germinal center and lymphoepithelial compartment of the caecal tonsil. The mesenchymal reticular cell, the basic supporting cell of the germinal center, was stained prominently by anti‐vimentin and anti‐desmin. Both antibodies stained the bursal cortex but only anti‐vimentin bound the bursal secretory dendritic cell of the medulla. In addition to being vimentin positive and desmin negative, the bursal secretory dendritic cell possessed and the follicular dendritic cell appeared to possess IgG on their surfaces. In all the observations, B‐cells were vimentin negative. Conclusion: These studies suggest that follicular dendritic cells and mesenchymal reticular cells in the caecal tonsil's germinal centers may be functionally different cell populations while the bursal secretory dendritic cell and follicular dendritic cell of the caecal tonsil may have a common origin.