Involution of Thymus During Pregnancy in Young Mice

Effects of pregnancy and lactation on lymphocytes in the bone marrow of the mouse: A quantitative electron microscopic study.

“…Recently we have reported that marrow lymphocytes show significant age-and sex-related changes and that the changes in marrow lymphocytes are similar in pattern to those in the thymus, the other central lymphatic tissue (SASAKI andITO, 1978, 1980). In relation to sex, it has been observed by earlier investigators (PERSIKE, 1940;GREGOIRE, 1947;ITO and HOSHINO, 1962) that pregnancy and lactation exert significant effects on the thymus.…”

“…Thus the pregnancy-induced changes in peripheral lymphatic tissues are generally explained primarily in view of the alloantigenic status of the mother to embryos, particularly allogeneic ones (MARONI and DE SOUSA, 1973;MCLEAN et al, 1974;ANSELL et al, 1978). Concerning the effects of pregnancy and lactation on the central lymphatic tissue, it has been reported that the thymus undergoes involution in late pregnancy (PERSIKE, 1940;GREGOIRE, 1947;PEPPER, 1961;ITO and HOSHINO, 1962;MILLAR et al, 1973;CLARKE, 1979), and that the thymus becomes extremely involuted at parturition and remains atrophic during lactation (ITO and HOSHINO, 1962;MCLEAN et al, 1974). As is generally accepted, the central lymphatic organ, such as the thymus, does not directly respond to antigenic stimulation, but reacts to various endocrine factors (review: WEISS, 1972).…”

REVIEW ARTICLE: Regulatory T Cells and Their Role in Pregnancy

“…56 During pregnancy, an 'involution' of thymus is also known to occur in a number of species including rat, mouse, and human. [57][58][59] However, contrary to what it happens during aging, there are strong evidences that the so-called 'involuted' maternal thymus is active during pregnancy despite suffering several morphological changes. 60,61 It is very likely that the so-called involution is just a remodeling process necessary to achieve tolerance.…”

Progesterone receptors in the thymus are required for thymic involution during pregnancy and for normal fertility

“…This blockade manifests itself grossly in the form of thymic involution and bone marrow involution. Involution of the thymus, the site of T cell differentiation, has long been recognized to occur during pregnancy in a number of species including rat, mouse, and human (11)(12)(13) and may be mimicked by the administration of the female sex hormones estrogen (E) and progesterone (P), although the relative contributions of the two hormones are controversial (14,15). Although the functional importance of pregnancy-induced thymic involution remains unknown, the fact that it has been observed in all mammals that have been examined has led to the speculation that reduced or altered output of mature T cells by the thymus could be an important component of maternal immune regulation.…”