Non‐lymphoid cells of the anuran spleen: An ultrastructural study in the natterjack, Bufo calamita

Abstract

The present study is concerned with the ultrastructure of the spleen in the natterjack, Bufo calamita (Anura, Bufonidae), with special emphasis on the structure and function of the non-lymphoid elements occurring in the red and white pulp. The organ consists of two clearly distinguishable areas, the white and the red pulp, separated by a prominent marginal zone. Thus, the pattern of lymphocytic arrangement in the spleen of Bufo calamita corresponds to a follicular model and is similar to that reported in the primitive anurans of the Pipidae family, such as Xenopus laevis. The white pulp presents a reticular network consisting of two different cell types and free cells, such as lymphocytes, plasma cells, and macrophages. The red pulp is formed by cell cords, where reticular cells and fibers, macrophages and lymphocytes occur, and blood sinuses which sometimes contain developing erythroid elements. Colloidal carbon particles injected via the lymph sac are trapped exclusively by free macrophages in the red pulp which then move through the marginal zone to the white pulp. Giant, ramified, non-phagocytic cells appear in both white and red pulp. They have been functionally related with the trapping of antigen-antibody complexes on their surface, and a possible dendritic significance is discussed on the basis of their morphologic characteristics.

Evolution of Myeloid Cells

“…A population of cells similar to the Xenopus XL cells has been described in another amphibian, the Natterjack toad ( Bufo calamata ) (109). In this study, colloidal carbon particles injected into the dorsal lymph sac were first captured by macrophages and then transported into the RP, where cells with a similar morphology to Xenopus XL cells were observed.…”

The architecture of the spleen of the yellow‐bellied toad, Bombina variegata

“…In general, the white pulp of mammalian spleen is organized into a periarteriolar lymphoid sheath and lymphoid follicles containing germinal centres, both surrounded by the marginal zone (Eikelenboom et al, 1985). However, the degree of development of the white pulp varies considerably among ectothermic vertebrates (Pitchappan, 1980;Zapata, 1983;Fange & Nilsson, 1985).…”

“…Among amphibians, in some urodeles (Tooze & Davies, 1967;Manning & Horton, 1982), and anurans from the genus Ascaphus (Cooper & Wright, 1976), the white pulp is not clearly defined, while in certain apodans (Welsch & Storch, 1982) and the anuran genus Scaphiopus (Cooper & Wright, 1976) the lymphocytes may form small aggregations. In contrast, in anurans from the genera Xenopus (Manning & Horton, 1982), Rana (Cooper & Wright, 1976) and Bufo (Diener & Nossal, 1966;Barrutia et al, 1983) the division into white and red pulp is well developed. However, the typical germinal centres have not so far been described in spleens of ectothermic vertebrates.…”

“…Among the latter, the spleen is present in all jawed vertebrates (Pitchappan, 1980). The spleen of dipnoans is embedded in the intestinal wall while in other fish and tetrapods it is a separate organ hanging in the mesentery near the intestine (for review see Zapata, 1983;Fange & Nilsson, 1985;Tischendorf, 1985).…”

“…However, the development of these two parts differs considerably among vertebrates (for review see Pitchappan, 1980). In this context the anuran amphibians seem very interesting as in this order of animals there are species which differ drastically in the degree of the development of the white pulp (Diener & Nossal, 1966;Cooper & Wright, 1976;Manning & Horton, 1982;Barrutia et al, 1983;Plytycz & Bigaj, 1983). However, although there are striking differences in the splenic morphology in anurans studied so far, these observations have been accumulated in a limited number of species.…”