IMMUNOREACTIVITY OF NEURAL CREST-DERIVED CELLS IN THYMIC TISSUE DEVELOPING UNDER THE RAT-KIDNEY CAPSULE

In order to study the functional development of a thymus in an experim ental model, small pieces of adult rat thymic tissue were cultured for 9 days and implanted under the kidney capsule of littermates. The tis sues were examined with a panel of antibodies raised against thymic an d neural factors and neural crest cells at intervals from 5 to 13 days . At 5 days post-implantation, there were groups of L1+ cells within t he implants that reacted with antibodies raised against neural and neu ral crest cell markers. L1+ cells were highly mitotic, rounded cells m easuring 8.7 +/- 0.6 mu m in diameter. Double immunostaining with diff erent combinations of antibodies showed that 94% of the L1+ cells were also TH+, and many were HNK-1/NCAM+, PCP 9.5+, NGF+, chromogranin A+. VIP+, S100+, CGRP+, GAD+, and A2B5+. A few were also pan-cytokeratin. These results indicate that these cells are derived from neural cres t derived cells and belong to the neuroepithelial line of development. The L1+ cells were most numerous before nerves appeared (about Day 9) and reduced in number and extent as the thymus differentiated. The ne ural crest cells occasionally had long cytoplasmic extensions, but it was not possible to decide if they formed the nerves that appeared in the implants. Adult thymuses also contained a population of L1+ and HN K-1/NCAM+ cells, mainly in the subcapsular cortex, the septa, and the medulla. These cells could be a sourer of neural crest cells able to r epopulate the implant. The adult thymus may always contain a reservoir of cells potentially capable of producing neuropeptides and transmitt er factors required for thymic growth and regeneration. (C) 1998 Acade mic Press.