Lympho-epithelial interactions in rat thymus during pregnancy.

Alterations in the thymic epithelial cell activity were analysed during pregnancy and lactation in Wistar rats by examining the presence and in situ distribution of lymphoepithelial complexes formed by thymic nurse cells (TNC). TNC were identified in paraffin sections by their expression of MHC class II antigens, CD54 molecule and a neuromarker, protein gene product 9.5 (PGP9.5). On the first days of pregnancy (gestational days, GD) the number of PGP9.5+ TNC was found to decrease abruptly. On GD 14, a transient increase was noted in the number of PGP9.5+, MHC+, CD54+ TNC. Another increase was observed in the course of lactation, when the weight of the thymus reached the lowest values. While the increase in TNC numbers during lactation may be linked to the process of reconstruction of the thymic lymphoid population, the augmented activity of lymphoepithelial interactions on GD14 may be associated with thymic engagement in pregnancy-induced immune processes.