Ovarian autoimmune disease: clinical concepts and animal models

Abstract

The ovary is not an immunologically privileged organ, but a breakdown in tolerogenic mechanisms for ovary-specific antigens has disastrous consequences on fertility in women, and this is replicated in murine models of autoimmune disease. Isolated ovarian autoimmune disease is rare in women, likely due to the severity of the disease and the inability to transmit genetic information conferring the ovarian disease across generations. Nonetheless, autoimmune oophoritis is often observed in association with other autoimmune diseases, particularly autoimmune adrenal disease, and takes a toll on both society and individual health. Studies in mice have revealed at least two mechanisms that protect the ovary from autoimmune attack. These mechanisms include control of autoreactive T cells by thymus-derived regulatory T cells, as well as a role for the autoimmune regulator (AIRE), a transcriptional regulator that induces expression of tissue-restricted antigens in medullary thymic epithelial cells during development of T cells. Although the latter mechanism is incompletely defined, it is well established that failure of either results in autoimmune-mediated targeting and depletion of ovarian follicles. In this review, we will address the clinical features and consequences of autoimmune-mediated ovarian infertility in women, as well as the possible mechanisms of disease as revealed by animal models.

Figure 1

Histological features of the normal post-pubertal ovary. These images show the structures of a post-pubertal mouse ovary; salient features of the human ovary are essentially the same. Major structures include follicles, which house the oocytes, and the post-ovulatory correlate of the follicle, the corpus luteum. Multiple follicles at various stages of development are present within the pre-senescent ovary at any given time. Several stages of follicles can be seen in this section, including the developmentally earliest stages, primordial and primary follicles (lower left and right insets), and the more advanced antral follicles (center and upper left inset). Oocytes are encased in follicular steroidogenic cells, the inner granulosa and the outer theca cell layers (upper left inset); theca interna and theca externa are not clearly depicted in this image but can be seen in Figure 4. Mature follicles and corpora lutea produce estrogen and progesterone, respectively, which are required sequentially for uterine preparation and maintenance of pregnancy. The sample is stained with hematoxylin and eosin. Scale bars: 100 µm (upper left); 50 µm (lower left); 1000 µm (center); 50 µm (right).

Figure 2

AIRE expression in mTEC of mouse thymic medulla. Immunohistochemical analysis of thymic medulla of a Balb/c mouse using a monoclonal anti-mouse Aire antibody. mTEC, although not universally Aire⁺, are distinguished by high cytoplasm/nucleus ratio; thymocytes are smaller cells with low cytoplasm/nucleus ratio. Red/brown stain indicates nuclear staining of Aire protein. Counterstain, hematoxylin. Scale bar=50 µm. AIRE, autoimmune regulator; mTEC, medullary thymic epithelial cell.

Figure 3

T lymphocyte infiltration into ovarian follicles of Aire-deficient mice. (a–c) Follicles from WT mice; (d–f) Follicles from Aire-deficient mice. (a, b, d, e) Hematoxylin and eosin stain; (c, f) Immunohistochemistry using anti-CD3 pan-T-cell antibody and hematoxylin counterstain. WT follicles lack detectable lymphocytes, while follicles from Aire-deficient mice are surrounded by T cells, including those in close contact with the degenerating oocyte. Arrowheads in d and e identify putative lymphocytes surrounding oocyte; CD3-positive cells can similarly be seen in proximity to the egg in f. AIRE, autoimmune regulator; WT, wild-type.

Figure 4

ZP3 expression in the murine thymic medulla is mediated by Aire. (a) ZP3 mRNA is abundant in the ovaries of both WT and Aire-deficient mice (KO) (right two bars), and is detectable in WT thymi but not KO thymi (left two bars). n=3–4 mice per condition. RQ, relative quantity with respect to a WT mouse ovary sample. (b–d) Immunohistochemical localization of ZP3 in the ovary and thymic medulla of a WT and a KO mouse. In the ovary (b; positive control), ZP3 immunoreactivity is observed surrounding the oocyte of an antral follicle (arrow) and a primary follicle. Nonspecific staining was also observed in the vicinity of vessels (*). In WT thymic medulla (c), ZP3 immunoreactivity is seen in large cells with abundant cytoplasm, presumably mTEC. Immunoreactivity was rare in thymi of Aire-deficient mice (d), although occasional positive cells were observed. Counterstain, hematoxylin. Scale bars=100 µm. AIRE, autoimmune regulator; GC, granulosa cells; ti, theca interna; te, theca externam TEC, medullary thymic epithelial cell; KO, knockout; WT, wild-type.

Figure 5

Anti-ovary serum autoantibodies are produced by Aire-deficient Balb/c mice. WT (n=5) and Aire-KO (n=15) mice were bred at approximately 6 weeks of age to intact WT Balb/c males. Presence of a copulation plug was confirmed visually, and females were euthanized 7–10 days later. All five WT mice and seven of 15 Aire-KO mice were confirmed pregnant. Sera were collected and used to probe a western blot of ovarian lysate from RAG2^−/− mice, fitted with a Mini-Protean II Multiscreen apparatus. Although band size and intensity varied between animals, nearly all Aire-deficient mice displayed serum autoreactivity against ovarian antigens. Prominent bands included ∼70 kD and ∼90 kD antigens in pregnant and non-pregnant animals, respectively. AIRE, autoimmune regulator; RAG, recombinase-activating gene; WT, wild-type.

Figure 6

Human CGA expression in the third trimester (term) human placenta (a) (positive control) and thymus (b). Human thymus immunoreactivity (red/brown stain) for CGA averaged 2–3 positive cells per high-powered field, and was only observed in epithelial cells in the medulla. Counterstain, hematoxylin. Scale bars=100 µm. CGA, chorionic gonadotropin A.