Reshaping of T-lymphocyte compartment in adult prepubertaly ovariectomised rats: a putative role for progesterone deficiency

Abstract

This study explores the role of ovarian hormones in the phenotypic shaping of peripheral T-cell pool over the reproductive lifespan of rats. For this purpose, 2-month-old prepubertally ovariectomised (Ox) rats, showing oestrogen and progesterone deficiency, and 11-month-old Ox rats, exhibiting only progesterone deficiency, were examined for thymus output, and cellularity and composition of major TCRαβ+ peripheral blood lymphocyte (PBL) and splenocyte subsets. Although ovariectomy increased thymic output in both 2- and 11-month-old rats, the count of both CD4+ and CD8+ PBLs and splenocytes increased only in the former. In the blood and spleen of 11-month-old Ox rats only the count of CD8+ cells increased. Although ovariectomy affected the total CD4+ count in none of the examined compartments from the 11-month-old rats, it increased CD4+FoxP3+ PBL and splenocyte relative proportions over those in the age-matched controls. The age-related differences in the cellularity and the major subset composition in Ox rats were linked to the differences in the ovarian steroid hormone levels registered in 2- and 11-month-old rats. The administration of progesterone to Ox rats during the seven days before the sacrificing confirmed contribution of this hormone deficiency to the ovariectomy-induced changes in the TCRαβ+ PBL and splenocyte pool from 11-month-old rats. The expansion of the CD8+ splenocyte subset in the 11-month-old Ox rats reflected increases in cellularity of memory and, particularly, naïve cells. This was due to greater thymic output of CD8+ cells and homeostatic proliferation than apoptosis in 11-month-old Ox rats when compared with age-matched sham-Ox control rats. The homeostatic changes within CD8+ splenocyte pool from 11-month-old Ox rats, most likely, reflected the enhanced splenic IL-7 and TGF-β mRNA expression. Overall, in adult female rats, circulating oestrogen and progesterone provide maintenance of T-cell counts, a diversity of T-cell repertoire, and the main T-cell subset composition in the periphery. Progesterone deficiency affects mainly the CD8+ lymphocyte compartment through increasing thymic CD8+ cell export and upsetting homeostatic regulation within the CD8+ splenocyte pool. These alterations were reversible through progesterone supplementation.

Keywords: 7-AAD; 7-amino-actinomycin D; AO; Albino Oxford; BSA; DDM; DTH; FCA; FCS; FITC; FSC; FoxP3; IFN-γ; IL; Immunoregulatory cytokines; MACS; NK; Ox; PBLs; PBS; PCR; PE; PerCP; Peripheral blood lymphocytes; Progesterone; RTEs; Reproductive lifespan; SSC; Splenocytes; T-cell subsets; TGF-β; bovine serum albumin; delayed-type hypersensitivity; doublet discrimination module; fetal calf serum; flow cytometric analysis; fluorescein isothiocyanate; forkhead box P3; forward scatter; interferon-γ; interleukin; mAbs; mRNA; magnetic-activated cell sorting; messenger ribonucleic acid; monoclonal antibodies; natural killer; ovariectomised; peridinin chlorophyll protein; peripheral blood lymphocytes; phosphate-buffered saline; phycoerythrin; polymerase chain reaction; recent thymic emigrants; side scatter; transforming growth factor-β.