In vitro behavior of thymic nurse cell‐like complexes from mechanically and enzymatically dissociated frog tadpole thymuses

Abstract

Cellular complexes, analogous by virtue of their external appearance, size, and number of seemingly internalized thymocytes to thymic nurse cells (TNCs) of endothermic vertebrates, were seen in short-term cultures (6-8 days) of mechanically and enzymatically dissociated thymuses of leopard frog tadpoles. Most TNC-like complexes from mechanically disrupted thymuses were covered with many thymocytes that morphologically resembled the "internalized" thymocytes. With time in culture, most complexes remained spherical and lost their externally adherent and "internalized" thymocytes. Some complexes, however, adhered to the glass substratum by means of macrophage-like cells. After one typically appearing TNC from a mechanically dissociated thymus had released its "internalized" thymocytes and spread completely over the glass substratum, it could be seen to consist actually of 9-10 stromal cells with the appearance of epithelial cells, macrophages, and dendritic cells. TNC-like structures from enzymatically dissociated thymuses had few, if any, attached thymocytes. Although these structures closely resembled murine TNCs initially, they displayed abnormal transformations within a few days of culture. Our observations led us to question the assumption that all TNCs from mechanically as well as enzymatically isolated TNCs from vertebrate thymuses are single cells. Rather, some if not all of the so-called TNC may actually be entities composed of several stromal cell types that enclose thymocytes. We suggest that this configuration seen in vitro may reflect the architecture of the compartmentalized reticular stromal cell meshwork that characterizes the intact thymus.

Thymic nurse cells: Their functional ultrastructure

“…It has already been noted that in vitro TNCs are frequently associated with populations of thymic nonlymphoid cells which are characteristic for a given type of complex. We share the opinion of Holtfreter and Cohen (1987) that multicellular structures released from the thymus during their isolation reflect variable cellular structures of individual thymic regions. Examining reciprocal relations of various cell types in the thymus in situ, we have been able to show (Brelinska et al, 1985) that thymocytes and various types of thymic nonlymphoid cells form multicellular complexes in a nonrandom manner, of a composition typical for a given zone of the organ.…”

Neuropeptides and thymic hormones in the Xenopus thymus

“…This staining was specific, as background staining was not detected in the negative control. However, the negative control did present high levels of endogenous peroxidase, activity which suggests the presence of high numbers of macrophage clusters associated with thymic nurse cells as previously described in amphibians (94,99). When looking at keratin expression, the Xenopus thymus was found to display a typical network of TEC although more globular in organisation (particularly in the medulla).…”