Differential Effects of Male and Female Gonadal Hormones on the Intrathymic T cell Maturation

The study was undertaken to further elucidate a role of gonadal hormones in maintenance of normal thymocyte maturation and sexual dimorphism in the intrathymic T-cell development. Rats of both sexes were gonadectomized or sham-gonadectomized (controls) at age of 2 and 6 months, and 30 days later the thymus size, cellularity and thymocyte composition were evaluated. In both control and gonadectomized rats, in spite of age, sexual dimorphism in the thymus size and cellularity was found. Gonadectomy in 2-month-old rats of both sexes increased the thymus cellularity, volumes of both cortex and medulla and thymus size (to a less extent in males), while in 6-month-old rats, in this respect, it was effective only in females. In ovariectomized (OVX) rats the increase in volume of cortex was more marked in younger rats, while that of medulla did not differ between rats of different age. It seems obvious that in both groups of OVX rats the volume of medullary non-lymphoid component was enlarged (the increase in medullary volume was more pronounced than that in its cellularity). Unlikely, in rats orchidectomized (ORX) at age of 2 months the volume of this component was either decreased or unaltered (the increase in the volume of medulla was less conspicuous than that in the number of medullary thymocytes). In control and gonadectomized rats of both ages, sexual dimorphism in the composition of thymocyte subsets was also observed. Gonadectomy in 2-month-old rats affected distinct stages of thymocyte maturation in male (increased the relative proportions of CD4+8+TCRαβlow cells and their CD4–8+TCRαβlow precursors and decreased those of the most mature CD4+8-TCRαβhigh and CD4–8+TCRαβhigh cells) and female rats (decreased only the percentage of the least mature CD4–8-TCRαβ-cells). In older rats only ovariectomy had impact on the relative proportion of thymocytes decreasing, besides the relative proportion of CD4–8-TCRαβ- cells, those of CD4–8+TCRαβ-, CD4–8+TCRαβlow, positively selected CD4+8+TCRαβhigh and the most mature CD4+8-TCRαβhigh, CD4–8+TCRαβhigh cells and exerting an opposite effect on the percentages of CD4+8+TCRαβ- and CD4+8+TCRαβlow cells. Thus, results showed sex- and age-dependent changes in sensitivity of both the developing thymocytes and non-lymphoid cells to long-lasting gonadal deprivation

Promene u modelu diferentovanja timocita u mužjaka pacova sa godinama

In order to elucidate the features of putative age-related changes in the intrathymic T cell maturation sequence, the thymus weight, thymocyte yield and relative proportions of thymocyte subsets were analyzed at distinct maturational stages (delineated by analysis of the expression of CD4/CD8 coreceptor molecules and TCR molecular complex) in male AO rats, from the peripubertal period (1 month of age) until 10 months of age. In 2-month-old rats both the thymus weight and lymphoid content were greater than in 1-month-old rats. The values of both parameters in 4-month-old rats were reduced to the corresponding values in 1-month-old rats. These levels were sustained until 10 months of age. However, the thymocyte composition was subjected to substantial changes during the whole period studied, probably due to alterations in action of both extrinsic and intrinsic factors which influence the ability of the thymus to support T cell maturation and/or feedback regulatory action of intrathymic CD4+ T cells on thymocytopoiesis (between the age of 7 and 10 months).U cilju definisanja karakteristika procesa sazrevanja T ćelija u timusu u funkciji uzrasta, u mužjaka pacova AO soja, različitog uzrasta (od 1 meseca do 10 meseci) posmatrane su: težina timusa, ukupan broj timocita, kao i relativna zastupljenost pojedinih timocitnih subpopulacija (koje su razdvojene na osnovu ekspresije CD4/8 koreceptornih molekula i antigena TCRαβ molekulskog kompleksa). U životinja uzrasta 2 meseca i težina timusa i ukupan broj timocita bili su značajno veći nego u životinja uzrasta od mesec dana. Međutim, u životinja uzrasta od 4 meseca vrednost ovih parametra nije se razlikovala od vrednosti odgovarajućih parametara sa mesec dana. Vrednosti oba ova parametra nisu se bitno menjale od 4. do 10. meseca života. Sa druge strane, naši rezultati su pokazali značajne promene u relativnom odnosu timocitnih subpopulacija u ispitivanom periodu. Ove promene se mogu objasniti promenama u delovanju, kako spoljašnjih tako i unutrašnjih, faktora koji modulišu sposobnost timusne mikrosredine da podrži proces sazrevanja T ćelija i/ili utiču na efikasnost regulatornog delovanja intratimusnih CD4+ T ćelija, mehanizmom negativne povratne sprege, na proces sazrevanja T ćelija u timusu

Alterations in thymopoiesis in intact and peripubertally orchidectomized adult rats of different age

In adult rats 3, 6 and 9 months post-orchidectomy performed at the age of 30 days the thymus weight, thymocyte yield and relative proportions of thymocyte subsets (delineated by expression of CD4/CD8 molecules and TCRalphabeta) were analyzed in order to elucidate a putative role of male gonadal hormones in the shaping of thymus size and intrathymic T cell Maturation, In 4-month-old control rats the thymus size and cellularity returned to the corresponding levels in 1-month-old rats, These levels were sustained during the following 6 months. In spite of that, the distribution of the main thymocyte subsets in these rats as Subjected to significant changes, probably due to an age-associated diminishing thymus ability to provide efficient T cell differentiation. The results added further v.,eight to a potential feedback regulatory role of CD4+8- cells in thymopoiesis. Furthermore. they revealed that the orchidectomy-induced (i) enlargement of the thymus size and enrichment of the thymic lymphoid cell content are of a limited duration and (ii) alterations in the relative proportion of thymocytes become quantitatively more pronounced with duration of the gonadal deprivation. Thus, the study also indicates that the age-associated changes in gonadal hormones may be, at least partly. responsible For the age-related reshaping a of the T cell maturation sequence, and hence for remodeling T cell dependent immune functions. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved

Castration of sexually immature rats affects sympathetic innervation of the adult thymus

It has been hypothesized that maturational processes within the hypothalamo-pituitary-gonadal (HPG) axis and thymus are reciprocally regulated via neural pathways. To test this hypothesis, in the thymi of adult rats orchidectomized (ORX) at age of 1 (ORX-1), 7 (ORX-7) and 30 days (ORX-30): (i) noradrenaline (NA), dopamine (DA) and serotonin (5-HT) contents and acetylcholinesterase (AChE) activity were measured and (ii) the distribution of monoamine- and AChE-containing nerves and cells was examined by a sucrose phosphate glyoxylic acid (SPG) method and enzyme histochemistry, respectively. In all groups of ORX rats, the thymus weight was significantly increased over that in sham-ORX control rats. In the ORX-1 rats, the increase in the thymus weight was accompanied by a proportional increase in the content of both catecholamines and 5-HT; consequently the concentration of each of them remained unaltered. In these animals, the density of both SPG-stained thymus nerve fibers and cells also remained unchanged. In the ORX-7 rats, the rise in the thymus weight was followed by a proportional increase in the content of all monoamines, except for NA which was reduced. Therefore, in these rats neither the thymus concentrations of DA nor that of 5-HT differed from controls, while the concentration of NA was significantly decreased. The reduction in both NA content and concentration reflected a diminished density of SPG-positive nerve profiles. In the ORX-30 rats, the increase in thymus weight was neither paralleled by a proportional increase in the DA content nor in 5-HT, while the content of NA was decreased. Thus, in their thymi the concentration of both NA and DA, as well as that of 5-HT, were significantly reduced. In parallel with these changes, a decreased density of thymic SPG-positive nerve fibers and cells was found. In all ORX rats, the pattern of intrathymic distribution of SPG-positive fibers and cells remained unchanged. Orchidectomy affected neither the activity of AChE (expressed per gram of tissue) nor the density of AChE-positive nerves and cells in the thymus. As the changes in the density of adrenergic nerve fibers in the thymus from ORX rats were not followed by similar alterations in the density of AChE-containing nerve fibers, it does not seem likely that NA and AChE are colocalized in the thymus nerve fibers. The results also suggest that there is a critical period during ontogenesis when changes within the HPG axis evoked by orchidectomy can affect the sympathetic nerve input to the rat thymus and therefore, most likely, development and function of the organ. Copyright (C) 2000 S. Karger AG, Basel

Orchidectomy affects the innervation of the rat thymus

To assess a putative role of the neural pathways in transfer of information from the gonads to the thymus, adult AO rats were orchidectomized (ORX) or sham ORX (controls); sacrificed 1, 3, 7, or 15 days later and their thymi were analyzed for: (a) the concentrations of noradrenaline (NA), dopamine (DA) and serotonin (5-HT) and distribution of monoamine-containing nerve profiles and (b) the acetylcholinesterase (AChE) activity and distribution of AChE-containing nerve profiles. Three days after the castration, an elevation in the level of both catecholamines, reflecting an increase in the overall intensity of nerve fibers autofluorescence, was found. Seven days post castration neither NA nor DA concentration differed from the appropriate control values, while 15 days after the surgery the concentration of NA was lower than that in the controls, most likely, due to diminished density of noradrenergic nerve profiles. In both the rats sacrificed 7 and 15 days after orchidectomy the concentration of 5-HT was reduced as result of a decrease in the density of 5-HT-containing autofluorescent cells. The activity of AChE was depressed one day after the surgery; then increased, so that 3 days post castration its value was higher than that in the sham ORX. After this increase, AChE activity decreased being, at postoperative day 7 and 15, lower than that in the controls. It seems that this decrease in AChE activity reflected, not only a reduction in the density of AChE-containing nerve fibers, but also a decrease in the density of AChE positive cells. Thus, the results indicate that orchidectomy can evoke changes in the T-cell maturation altering modulatory influences on this process coming via neural route, as well as those coming from the mast cells and AChE positive epithelial cells which constitute important component of the thymus microenvironment

In vivo modulation of the distribution of thymocyte subsets by female sex steroid hormones

This study examined the effects of the principal ovarian steroids, 17β-estradiol (E) and progesterone (P), on the thymic structure and on the intrathymic development of T-cells. Adult female rats were ovariectomized (OVX) and treated for 14 days with physiological doses of either E or P; controls received an equivalent volume of vehicle. Ovariectomy produced a marked increase (vs. sham-operated controls) in thymus weight, which was associated with an increase in the volume and cellularity of both the medulla and cortex. Treatment of OVX rats with E reduced the thymic weight to value, which was significantly lower than that of sham-operated controls decreasing the volume of cortex below level in sham-OVX rats, and reversing the effect of ovariectomy on the volume of medulla. P only prevented the increases in thymus weight and cortical volume induced by OVX. However, unlike E, it had no discernable effect on the medullary volume. E treatment reduced the cellularity of the cortex and medulla to values, which were lower than those of sham-OVX rats, while P only reversed the effects of OVX on the cellularity of both the compartments. Ovariectomy also had a profound effect on the thymocyte profile, increasing the proportion of CD4 + 8 + TCRαβ - cells and producing a corresponding decrease in the relative proportions of all TCR αβ high cell subsets. The decrease in the latter was opposed by treatment with E or P. However, the sensitivity of the less mature cells (except CD4 - 8 - TCR αβ - , the percentage of which was reduced by both hormones) to the two hormones differed. E reduced the relative proportion of CD4 - 8 + TCRαβ - , CD4 - 8 + TCRαβ low and CD4 + 8 + TCRαβ - cells, while P increased the percentage of CD4 - 8 + TCRαβ low cells. The results suggest that E and P affect both the lymphoid and nonlymphoid compartments of the thymus, and that while P increases the volume of the nonlymphoid component of the medulla, E has the opposite effect. The finding that ovariectomy decreased while E and P increased the relative proportion of the most mature thymocytes, which include CD4 - 8 - TCRαβ high cells that are believed to harbour potentially autoreactive cell clones, is particularly interesting and may relate to the high propensity of autoimmune diseases in females

In vivo modulation of the splenocyte yield and composition by female sex steroid hormones

The study was designed to shed more light on the controversial role of the two main ovarian steroid hormones (i.e. estradiol and progesterone) in shaping the size and phenotypic characteristics of the splenic lymphocyte pool. For this purpose ovariectomized adult rats (OVX) were treated for 14 subsequent days with either estradiol or progesterone (to attain physiological concentrations of the hormones). Afterwards, the splenocyte yield, and overall number of splenocytes bearing TCR alpha beta receptor, CD4 and CD8 coreceptor were evaluated. Fourteen-day-long ovarian hormone deprivation produced an increase in the splenic weight and splenocyte yield ton the account of a rise in the number of TCR alpha beta (-) cells), although the number of TCR alpha beta (+) cells was reduced as a result of a decrease in the size of the CD4(+) cell subpopulation. Replacement of either estradiol or progesterone prevented the increase hn splenic weight and reduced the splenocyte yield to values significantly lower than that in sham-OVX rats. Both the treatments completely abolished the effect of ovariectomy on the size of TCR alpha beta (-) cell population, but had differential effects on that of TCR alpha beta (+) cell population: estradiol did not affect its size, while progesterone caused a reduction on the account of a decrease in the numbers of both CD4+ and CD8(+) cells. The results suggest that: a) estradiol and progesterone have similar effects on the size of the splenic B cell population and that replacement of either estradiol or progesterone can prevent the effects of ovariectomy on the size of this population and b) estradiol does not affect while progesterone reduces the size of splenic T cell population. Thus, replacement of none of them is able to compensate the removal of gonads

Neonatal androgenization affects the intrathymic T-cell maturation in rats

The thymus structure, expression of CD4/CD8/TCR alpha beta on thymocytes and thymocyte proliferative and apoptotic indexes were analyzed in sexually immature 30-day-old and in sexually mature 60-day-old female rats neonatally androgenized (NA) by subcutaneous injection of 500 mu g testosterone propionate/day on days 1-3 and in their vehicle-administered counterparts. The treatment affected normal thymus development. Thus, at 30 days of age, there was a reduction in the thymus weight, reflecting a decrease in the main thymic compartments. However, at 60 days of age, thymus weight did not significantly differ from that in age-matched controls, since the cortical volume enlargement was followed by a proportional decrease in the medullary volume. In rats of both ages, the changes in thymic compartments most likely reflected alterations in the size of both lymphoid and nonlymphoid components. Furthermore, in NA rats, substantial changes in thymocyte phenotypic characteristics were registered, in spite of their age. In both groups of NA rats, a decrease in the relative proportion of the least mature CD4-8-TCR alpha beta- cells and in that of CD4+8- TCR alpha beta-/TCR alpha beta(low) cells followed by an increase in the percentage of their successor CD4+8+TCR alpha beta-/TCR alpha beta(low) cells was detected. In addition, in 30-day-old NA rats, the relative proportions of CD4+8+TCR alpha beta(high) cells ( just positively selected) and that of mature single positive (CD4+8- and CD4-8+) and CD4-8- double negative TCR alpha beta(high) cells, were reduced, while in 60-day-old NA rats only the percentage of CD4+8+TCR alpha beta(high) thymocytes was decreased. Thus, the study showed that the changes in the development of the hypothalamo-pituitary-gonadal axis induced by neonatal androgenization may affect the thymus development and intrathymic T-cell maturation. Copyright (C) 2005 S. Karger AG, Basel