Abstract
Numerous large, mitotically active cells with abundant electron lucent cytoplasm, large hyperlobated nuclei and prominent nucleoli are found in the periphery of the splenic white pulp follicles of healthy Xenopus laevis. Like mammalian dendritic cells, these cells are located in B-lymphocyte-rich splenic follicles and have long cytoplasmic processes that are in intimate contact with adjacent lymphocytes. Some of the cytoplasmic processes extend through the Tlymphocyte-rich marginal zone into red pulp and appear to trap and transport foreign material (colloidal carbon and human IgG) from its initial site of entry in the splenic red pulp into the white pulp. In contrast to macrophages, these cells do not phagocytose large quantities of carbon. They also fail to stain for the non-specific esterase, either in a diffuse pattern characteristic for macrophages or in the punctate pattern found in most lymphoid cells in this species. In contrast to adjacent B-lymphocytes in the white pulp follicle, they do not stain for cytoplasmic Ig. Unlike T-lymphocytes, early thymectomy does not interfere with their development (1). Thus, this cell may well be a primitive follicular dendritic cell. If so, it offers insights into the function of the Xenopus spleen, and the phylogenetic origin of dendritic cells.
Published Version
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