Review on Recent Topics in Hypophysitis.

The number of cases of lymphocytic hypophysitis is small, although the condition is not rare. For optimal therapy, the correct diagnosis from imaging, immunological studies, and pathological findings from a pituitary biopsy is important. Recently, anti-Rabphilin antibody has been proposed to be a biomarker for lymphocytic infundibulo-neurohypophysitis. Immunological disorders such as anti-Pit-1 antibody syndrome are similar to the pathogenesis of lymphocytic hypophysitis. Moreover, recent immune checkpoint blockade such ipilimumab has been shown to induce anti-CTLA-4-related hypophysitis. In the future, elucidating the immunological mechanism and establishing a suitable therapy will be necessary for accurate long-term prognosis.

A Novel Clinical Entity of Autoimmune Endocrinopathy: Anti-PIT-1 Antibody Syndrome.

Pituitary-specific transcription factor 1 (PIT-1; POU domain, class 1, transcription factor 1 (POU1F1)) is an essential transcription factor for the differentiation of somatotrophs, lactotrophs, and thyrotrophs, and for the expression of growth hormone (GH), prolactin (PRL), and thyroid-stimulating hormone (TSH). Mutations in PIT-1 cause congenital defects in GH and PRL secretion and severe TSH insufficiency. Anti-PIT-1 antibody syndrome, firstly reported in 2011, is characterized by acquired GH, PRL, and TSH deficiencies without PIT-1 mutation and is associated with the presence of the circulating antibody against PIT-1 protein as a marker. Various autoantibodies are detected with multiple endocrine organopathies in this syndrome; therefore, it meets the criteria of autoimmune polyglandular syndrome. Mechanistically, cytotoxic T lymphocytes specifically reacting with PIT-1 protein play an important role in the development of this syndrome.

[A Novel Clinical Entity "Anti-PIT-1 Antibody Syndrome"--Autoimmunity against a Transcription Factor].

Autoimmunity against the pituitary has been observed in patients with hypophysitis. Although various autoantibodies against pituitary proteins have been reported, it is known that most of them are markers for the disease. Recently, a unique autoantibody against pituitary transcription factor PIT-1 (POU1F1) was detected in patients with an acquired combined pituitary hormone deficiency characterized by a specific defect in growth hormone (GH), prolactin (PRL), and thyroid-stimulating hormone (TSH). The antibody has been suggested to be involved in the pathogenesis because PIT-1 is an essential transcription factor that plays a role in the differentiation and maintenance of GH-, PRL-, and TSH-producing cells and mutations in the PIT-1 gene, resulting in a specific defect in these hormones. This syndrome was found to be a novel clinical entity; therefore, it was named 'anti-PIT-1 antibody syndrome'. Circulating anti-PIT-1 antibody and various autoantibodies were detected with multiple endocrine organopathy, meeting the definition of autoimmune polyglandular syndrome. Mechanistically, cytotoxic T lymphocytes that specifically react with PIT-1 protein play an important role in the development of this syndrome. In this review, we discuss the clinical aspects and pathophysiology of anti-PIT-1 antibody syndrome.

Anti-PIT-1 antibody syndrome; a novel clinical entity leading to hypopituitarism.

Various hypothalamic-pituitary diseases cause hypopituitarism. Inflammation related to autoimmunity also causes hypopituitarism. Hypophysitis is a representative disease caused by autoimmunity. Generally, anterior pituitary hormones are non-specifically impaired in this condition, but specific hormone defects have been reported in some cases. Anti-PIT-1 (pituitary-specific transcription factor 1) antibody syndrome is a novel clinical entity that presents an acquired combined pituitary hormone deficiency characterized by a specific defect in growth hormone, prolactin, and thyroid-stimulating hormone. Circulating anti-PIT-1 antibody along with various autoantibodies are detected with multiple endocrine organopathy, meeting the definition of autoimmune polyglandular syndrome. Mechanistically, cytotoxic T lymphocytes that specifically react with PIT-1 protein play an important role in the development of this syndrome.

Involvement of PIT-1-reactive cytotoxic T lymphocytes in anti-PIT-1 antibody syndrome.

CONTEXT: Anti-pituitary-specific transcriptional factor 1 (PIT-1) antibody syndrome is characterized by acquired growth hormone (GH), prolactin (PRL), and thyroid-stimulating hormone (TSH) deficiencies associated with circulating anti-PIT-1 antibodies. Although autoimmunity to PIT-1 has been suggested as a pathogenesis, the precise mechanism of the syndrome remains unclarified. OBJECTIVE: To elucidate the involvement of antibody- or cell-mediated immunity in anti-PIT-1 antibody syndrome. MATERIALS AND METHODS: To investigate a direct effect of anti-PIT-1 antibody on pituitary cells, cell proliferation, and cytotoxicity detection assays were performed using patient serum. Enzyme-linked immunospot (ELISpot) assay was performed to evaluate the involvement of PIT-1-reactive cytotoxic T lymphocytes (CTLs). An immunohistochemical analysis using anti-CD4 or anti-CD8 antibody was performed to examine tissue infiltration by CTLs. RESULTS: Patient serum did not exhibit any inhibitory effect on cell proliferation and secretion of GH and PRL in GH3 cells. In addition, complement-dependent cytotoxicity was not detected in patient serum on GH3 cells or primary pituitary cells. The ELISpot assay revealed the presence of CTLs that specifically reacted to the recombinant PIT-1 protein in the patient's peripheral lymphocytes. CD8(+) cell infiltrations, which is the characteristic of CTLs, were observed in the pituitary gland, adrenal gland, stomach, thyroid gland, liver, and pancreas of the patient with anti-PIT-1 antibody syndrome. CONCLUSIONS: These results suggest that the anti-PIT-1 antibody is not a cause but a marker of anti-PIT-1 antibody syndrome, in which CTLs play a pivotal role in the pathogenesis.

A missense single-nucleotide polymorphism in the sialic acid acetylesterase (SIAE) gene is associated with anti-PIT-1 antibody syndrome.

A novel clinical entity related to autoimmune polygladular syndrome (APS) termed "anti-PIT-1 antibody syndrome" is characterized by a presence of circulating autoantibody against the pituitary-specific transcriptional factor-1 (PIT-1) with acquired specific defect in GH, PRL, and TSH. Although autoimmunity to PIT-1 has been suggested, the underlying mechanisms remain to be elucidated. Sialic acid acetylesterase (SIAE) plays a crucial role in regulating the threshold of autoantibody production of B-cells and the defective variants of SIAE are associated with an increased risk of various autoimmune diseases such as type 1 diabetes (T1DM). To explore the link between anti-PIT-1 antibody syndrome and SIAE, we analyzed SIAE gene in 3 patients with anti-PIT-1 antibody syndrome and 200 healthy control subjects, and compared the prevalence of single nucleotide polymorphisms. Intriguingly, we found A467V SIAE variants (c.1400C>T, rs7941523) in a heterozygous state in all the patients with anti-PIT-1 antibody syndrome, while we detected in 6 % of control subjects, in which the prevalence was significantly increased in the patients (P<0.0005). Considering the physiological function of SIAE and the clinical features of anti-PIT-1 antibody syndrome, present data imply a novel aspect of the pathogenesis in this disease.

Adult combined GH, prolactin, and TSH deficiency associated with circulating PIT-1 antibody in humans.

The pituitary-specific transcriptional factor-1 (PIT-1, also known as POU1F1), is an essential factor for multiple hormone-secreting cell types. A genetic defect in the PIT-1 gene results in congenital growth hormone (GH), prolactin (PRL), and thyroid-stimulating hormone (TSH) deficiency. Here, we investigated 3 cases of adult-onset combined GH, PRL, and TSH deficiencies and found that the endocrinological phenotype in each was linked to autoimmunity directed against the PIT-1 protein. We detected anti-PIT-1 antibody along with various autoantibodies in the patients' sera. An ELISA-based screening revealed that this antibody was highly specific to the disease and absent in control subjects. Immunohistochemical analysis revealed that PIT-1-, GH-, PRL-, and TSH-positive cells were absent in the pituitary of patient 2, who also had a range of autoimmune endocrinopathies. These clinical manifestations were compatible with the definition of autoimmune polyendocrine syndrome (APS). However, the main manifestations of APS-I--hypoparathyroidism and Candida infection--were not observed and the pituitary abnormalities were obviously different from the hypophysitis associated with APS. These data suggest that these patients define a unique "anti-PIT-1 antibody syndrome," related to APS.