Peripubertal ovariectomy provides long-term postponement of age-associated decline in thymic cellularity and T-cell output

Abstract

The present study was undertaken to reassess the recentlychallenged role of ovarian hormones in age-associated thymicinvolution. For this purpose, in eleven-month-old peripubertallyovariectomized(Ox)ratsweanalyzed:i)thymicweightandcellularity,ii)size of CD4+CD8+ double-positive (DP) thymocyte population, whichis believed to correlate to the thymic capacity to export mature T cells,iii) number of recent thymic emigrants (RTEs), and iv) number ofperipheral blood CD4+ and CD8+ lymphocytes. It was found that boththymic weight and cellularity were greater in Ox than in control rats. Inaddition, in Ox rats the numbers of DP thymocytes and both CD4+ andCD8+ RTEs, were significantly greater than in controls, indicating amore efficient generation of T cells in these rats. Furthermore, thesefindings, coupled with data indicating that the number of neither CD4+nor CD8+ peripheral blood lymphocytes was affected by ovariectomy,most likely, suggest a reduced homeostatic proliferation of memorycells in Ox rats, i.e. broadening of TCR peripheral repertoire withoutchanges in the overall number of T cells leading to a more efficientresponse to newly encountered antigens. The results indicate that theovarian steroid deprivation from early peripubertal period leads to along lasting postponement/alleviation of age-associated decline in T-cell mediated immune response.Key words: ovariectomy, ageing, thymic cellularity, recent thymicemigrants